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Versions: 00 01 02 03 draft-ietf-sacm-nea-swid-patnc

SACM                                                           C. Coffin
Internet-Draft                                                 D. Haynes
Intended status: Standards Track                              C. Schmidt
Expires: March 16, 2017                            The MITRE Corporation
                                                     J. Fitzgerald-McKay
                                                   Department of Defense
                                                      September 12, 2016


               Software Message and Attributes for PA-TNC
                  draft-coffin-sacm-nea-swid-patnc-02

Abstract

   This document specifies the Software Message and Attributes for PA-
   TNC.  It extends the PA-TNC specification [RFC5792] by providing
   specific attributes and message exchanges to allow endpoints to
   report their software inventory information to a NEA server (as
   described in [RFC5209]).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 16, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Scope and Audience  . . . . . . . . . . . . . . . . . . .   4
     1.2.  Keywords  . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  Supported Use Cases . . . . . . . . . . . . . . . . . . .   7
       2.1.1.  Use Software Inventory as a Factor in Determining
               Endpoint Access . . . . . . . . . . . . . . . . . . .   8
       2.1.2.  Maintain a Central Repository Reflecting an
               Endpoint's Software Inventory . . . . . . . . . . . .   8
       2.1.3.  PA-TNC Use Cases  . . . . . . . . . . . . . . . . . .   9
     2.2.  Non-supported Use Cases . . . . . . . . . . . . . . . . .   9
     2.3.  Specification Requirements  . . . . . . . . . . . . . . .  10
     2.4.  Non-Requirements  . . . . . . . . . . . . . . . . . . . .  11
     2.5.  Assumptions . . . . . . . . . . . . . . . . . . . . . . .  11
     2.6.  Non-Assumptions . . . . . . . . . . . . . . . . . . . . .  12
     2.7.  Software Message and Attributes for PA-TNC Diagram
           Conventions . . . . . . . . . . . . . . . . . . . . . . .  12
   3.  Software Message and Attributes for PA-TNC System
       Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  13
     3.1.  Basic Inventory Exchange  . . . . . . . . . . . . . . . .  13
     3.2.  Software Identifiers  . . . . . . . . . . . . . . . . . .  14
       3.2.1.  Record Identifiers  . . . . . . . . . . . . . . . . .  15
       3.2.2.  Using Software and Record Identifiers in SW
               Attributes  . . . . . . . . . . . . . . . . . . . . .  16
     3.3.  Targeted Requests . . . . . . . . . . . . . . . . . . . .  16
     3.4.  Monitoring Changes in an Endpoint's Software Inventory
           Evidence Collection . . . . . . . . . . . . . . . . . . .  17
     3.5.  Reporting Change Events . . . . . . . . . . . . . . . . .  19
       3.5.1.  Change Event Records  . . . . . . . . . . . . . . . .  20
       3.5.2.  Updating Inventory Knowledge Based on Events  . . . .  21
       3.5.3.  Using Event Records in SW Attributes  . . . . . . . .  22
       3.5.4.  Partial and Complete Lists of Event Records in SW
               Attributes  . . . . . . . . . . . . . . . . . . . . .  22
       3.5.5.  Synchronizing Event Identifiers and Epochs  . . . . .  24
     3.6.  Subscriptions . . . . . . . . . . . . . . . . . . . . . .  26
       3.6.1.  Establishing Subscriptions  . . . . . . . . . . . . .  26
       3.6.2.  Managing Subscriptions  . . . . . . . . . . . . . . .  27
       3.6.3.  Terminating Subscriptions . . . . . . . . . . . . . .  27
       3.6.4.  Subscription Status . . . . . . . . . . . . . . . . .  28
       3.6.5.  Fulfilling Subscriptions  . . . . . . . . . . . . . .  28
         3.6.5.1.  Subscriptions Reporting Inventories . . . . . . .  30



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         3.6.5.2.  Subscriptions Reporting Events  . . . . . . . . .  30
         3.6.5.3.  Targeted Subscriptions  . . . . . . . . . . . . .  31
         3.6.5.4.  No Subscription Consolidation . . . . . . . . . .  32
         3.6.5.5.  Delayed Subscription Fulfillment  . . . . . . . .  32
     3.7.  Multiple Sources of Software Inventory Evidence Records .  33
     3.8.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  34
   4.  Software Message and Attributes for PA-TNC Protocol . . . . .  36
     4.1.  PA Subtype (AKA PA-TNC Component Type)  . . . . . . . . .  36
     4.2.  PB-TNC and PA-TNC Messages  . . . . . . . . . . . . . . .  36
     4.3.  PA-TNC Attribute Header . . . . . . . . . . . . . . . . .  37
     4.4.  SW Attribute Overview . . . . . . . . . . . . . . . . . .  38
     4.5.  SW Attribute Exchanges  . . . . . . . . . . . . . . . . .  40
     4.6.  Software Message and Attributes for PA-TNC Attribute
           Enumeration . . . . . . . . . . . . . . . . . . . . . . .  42
     4.7.  Normalization of Text Encoding  . . . . . . . . . . . . .  43
     4.8.  Request IDs . . . . . . . . . . . . . . . . . . . . . . .  44
     4.9.  SW Request  . . . . . . . . . . . . . . . . . . . . . . .  45
     4.10. Software Identifier Inventory . . . . . . . . . . . . . .  48
     4.11. Software Identifier Events  . . . . . . . . . . . . . . .  51
     4.12. Software Inventory  . . . . . . . . . . . . . . . . . . .  56
     4.13. Software Events . . . . . . . . . . . . . . . . . . . . .  58
     4.14. Subscription Status Request . . . . . . . . . . . . . . .  62
     4.15. Subscription Status Response  . . . . . . . . . . . . . .  62
     4.16. PA-TNC Error as Used by Software Message and Attributes
           for PA-TNC  . . . . . . . . . . . . . . . . . . . . . . .  64
       4.16.1.  SW_ERROR,           SW_SUBSCRIPTION_DENIED_ERROR and
                SW_SUBSCRIPTION_ID_REUSE_ERROR Information . . . . .  66
       4.16.2.  SW_RESPONSE_TOO_LARGE_ERROR Information  . . . . . .  68
       4.16.3.  SW_SUBSCRIPTION_FULFILLMENT_ERROR Information  . . .  69
   5.  Supported Data Models . . . . . . . . . . . . . . . . . . . .  71
     5.1.  ISO 2015 SWID Tags using XML  . . . . . . . . . . . . . .  71
       5.1.1.  Guidance on Normalizing Source Data to ISO 2015 SWID
               Tags using XML  . . . . . . . . . . . . . . . . . . .  72
       5.1.2.  Guidance on Creation of Software Identifiers from ISO
               2015 SWID Tags  . . . . . . . . . . . . . . . . . . .  72
     5.2.  ISO 2009 SWID Tags using XML  . . . . . . . . . . . . . .  72
       5.2.1.  Guidance on Normalizing Source Data to ISO 2015 SWID
               Tags using XML  . . . . . . . . . . . . . . . . . . .  72
       5.2.2.  Guidance on Creation of Software Identifiers from ISO
               2015 SWID Tags  . . . . . . . . . . . . . . . . . . .  73
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  73
     6.1.  Evidentiary Value of Software Inventory Evidence Records   73
     6.2.  Sensitivity of Collected Records  . . . . . . . . . . . .  74
     6.3.  Integrity of Endpoint Records . . . . . . . . . . . . . .  75
     6.4.  SW-PC Access Permissions  . . . . . . . . . . . . . . . .  75
     6.5.  Sanitization of Record Fields . . . . . . . . . . . . . .  76
     6.6.  PA-TNC Security Threats . . . . . . . . . . . . . . . . .  76
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  76



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   8.  Relationship to Other Specifications  . . . . . . . . . . . .  77
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  77
     9.1.  Registry for PA-TNC Attribute Types . . . . . . . . . . .  77
     9.2.  Registry for PA-TNC Error Codes . . . . . . . . . . . . .  78
     9.3.  Registry for PA Subtypes  . . . . . . . . . . . . . . . .  79
     9.4.  Registry for Software Data Models . . . . . . . . . . . .  80
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  80
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  80
     10.2.  Informative References . . . . . . . . . . . . . . . . .  80
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  81

1.  Introduction

1.1.  Scope and Audience

   The Network Endpoint Assessment (NEA) Working Group defines an open
   solution architecture that enables network operators to collect and
   utilize information about endpoint configuration and state.  This
   information can be used to enforce policies, monitor endpoint health,
   and for many other activities.  Information about the software
   present on an endpoint is an important consideration for such
   activities.  Such information can come from multiple sources,
   including tag files (such as ISO SWID tags [SWID], reports from third
   party inventory tools, output from package managers, and other
   sources.  The attributes defined in this document are used to
   communicate software inventory evidence, collected from a range of
   possible sources, from the posture collector on the endpoint to the
   posture validator on a NEA Server using the PA-TNC interface, as
   shown in Figure 1 below.






















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       +-------------+                          +--------------+
       |  Posture    |   <--------PA-------->   |   Posture    |
       |  Collectors |                          |   Validators |
       |  (1 .. N)   |                          |   (1 .. N)   |
       +-------------+                          +--------------+
             |                                         |
             |                                         |
             |                                         |
       +-------------+                          +--------------+
       |   Posture   |                          |   Posture    |
       |   Broker    |   <--------PB-------->   |   Broker     |
       |   Client    |                          |   Server     |
       +-------------+                          +--------------+
             |                                         |
             |                                         |
       +-------------+                          +--------------+
       |   Posture   |                          |   Posture    |
       |   Transport |   <--------PT-------->   |   Transport  |
       |   Client    |                          |   Server     |
       |   (1 .. N)  |                          |   (1 .. N)   |
       +-------------+                          +--------------+
          NEA CLIENT                               NEA SERVER


                       Figure 1: NEA Reference Model

   This specification defines a new set of PA-TNC attributes, carried
   over PA-TNC messages, which are used to communicate requests for
   software information and software events, and for conveying that
   information back to a NEA Server.

   Possession of a list of an endpoint's installed software is very
   useful in understanding and maintaining the security state of an
   enterprise.  For example, if an enterprise policy requires the
   presence of certain pieces of software and/or prohibits the presence
   of other software, reported software inventory lists can be used to
   indicate compliance or non-compliance with these requirements.
   Software presence and the patch level of that software can be
   compared to vulnerability or threat alerts to determine an endpoint's
   exposure to attack.  All of these uses make an understanding of an
   endpoint's software collection highly useful to NEA Servers and other
   enterprise security applications.

   Before reading this specification any further, the reader should
   review and understand the NEA reference architecture as described in
   the Network Endpoint Assessment (NEA): Overview and Requirements
   [RFC5209].  The reader should also understand the capabilities and




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   requirements common to PA-TNC interfaces as defined in RFC 5792
   [RFC5792].

   This document is based on standards published by the Trusted
   Computing Group's Trusted Network Communications (TNC) workgroup.
   The TNC and NEA architectures are interoperable and the following
   components are equivalent:

     +---------------------------------------+-----------------------+
     | TNC Component                         | NEA Component         |
     +---------------------------------------+-----------------------+
     | Integrity Measurement Verifier (IMV)  | Posture Validator     |
     |                                       |                       |
     | Integrity Measurement Collector (IMC) | Posture Collector     |
     |                                       |                       |
     | TNC Server (TNCS)                     | Posture Broker Server |
     |                                       |                       |
     | TNC Client (TNCC)                     | Posture Broker Client |
     +---------------------------------------+-----------------------+

        Table 1: Equivalent components in TNC and NEA architectures

1.2.  Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   specification are to be interpreted as described in RFC 2119
   [RFC2119].  This specification does not distinguish blocks of
   informative comments and normative requirements.  Therefore, for the
   sake of clarity, note that lower case instances of must, should, etc.
   do not indicate normative requirements.

1.3.  Definitions

   This section defines terms with special meaning within this document.

   SW-PC - A Posture Collector (PC) that conforms to this specification.
   Note that such a posture collector might also support other PA-TNC
   exchanges beyond Software Message and Attributes for PA-TNC.

   SW-PV - A Posture Validator (PV) that conforms to this specification.
   Note that such a posture verifier might also support other PA-TNC
   exchanges beyond Software Message and Attributes for PA-TNC.

   SW Attribute - This is a PA-TNC attribute (as defined in RFC 5792
   [RFC5792] extension for conveying software inventory information.
   This specification defines several new attribute types.




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   Endpoint's Software Inventory Evidence Collection - The set of
   information regarding the set of software installed on an endpoint
   and expressed using one of the Software Message and Attributes data
   models, as described in the Software Data Model IANA table (see
   Section 9.4.  An endpoint's software inventory evidence collection
   might include information created by or derived from multiple
   sources, including but not limited to SWID tag files deposited on the
   file system during software installation, information generated to
   report output from software discovery tools, and information
   dynamically generated by a software or package management system on
   an endpoint.

   Software Inventory Evidence Record - The endpoint's Software
   Inventory Evidence Collection is composed of "records".  Each record
   corresponds to one installed instance of a particular software
   product as reported by some data source.  It is possible for a single
   installed instance to have multiple software inventory evidence
   records in an endpoint's Software Inventory Evidence Collection -
   this can happen if multiple sources all report the same software
   installation instance.

   Software Identifier - A string associated with a specific version of
   a specific software product.  Each supported Software Message and
   Attributes for PA-TNC data model has its own rules for how a Software
   Identifier (see Section 3.2) is derived from the representation of
   the given software product using that data model, and different
   sources for this information might populate relevant information
   differently.  As such, while each Software Identifier uniquely
   identifies a specific software product, the same software product
   might be associated with multiple Software Identifiers reflecting
   differences between different information sources and supported data
   models.

2.  Background

2.1.  Supported Use Cases

   This section describes the Software Message and Attributes for PA-TNC
   use cases supported by this specification.  The primary use of
   exchanging software inventory information over the PA-TNC interface
   is to enable a challenger (e.g.  NEA Server) to obtain inventory
   evidence about some system in a way that conforms to NEA procedures
   and expressed using a standard format.  Collected software
   information can support a range of security activities including
   determining whether an endpoint is permitted to connect to the
   enterprise, determining which endpoints contain software that
   requires patching, and similar activities.




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2.1.1.  Use Software Inventory as a Factor in Determining Endpoint
        Access

   Some enterprises might define security policies that require
   connected endpoints to have certain pieces of security software
   installed.  By contrast, some security policies might prevent access
   by endpoints that have certain prohibited pieces of software
   installed, such as applications that pose known security risks.  To
   support such policies, the NEA Server needs to collect evidence
   indicating the software inventory of an endpoint that is seeking to
   initiate or continue connectivity to the enterprise.

   Software Message and Attributes for PA-TNC facilitates policy
   decisions that consider an endpoint's software inventory by providing
   the NEA Server with software inventory information from the endpoint.
   The SW-PC can provide a complete or partial inventory to the SW-PV as
   required to determine policy compliance.  The SW-PV can then use this
   as evidence of compliance or non-compliance with enterprise policy.

2.1.2.  Maintain a Central Repository Reflecting an Endpoint's Software
        Inventory

   Many tools can use information about an endpoint's software inventory
   to monitor and enforce the security of an enterprise.  For example, a
   software patching service can use an endpoint's software inventory to
   determine whether certain endpoints have software that requires
   patching.  A vulnerability management tool might identify endpoints
   with known vulnerabilities (patched or otherwise) and use this to
   gauge enterprise exposure to attack.  A license management tool might
   verify that all copies of a particular piece of software are
   accounted for within the enterprise.  The presence of a central
   repository representing a real-time understanding of each endpoint's
   software inventory facilitates all such activities.  Using a central
   repository that can ensure the freshness of its collected information
   is generally more efficient than having each tool collect the same
   inventory information from each endpoint individually and leads to a
   more consistent understanding of enterprise state.

   Software Message and Attributes for PA-TNC supports this activity
   through a number of mechanisms.  As noted above, it allows a SW-PC to
   provide a complete list of software present in an endpoint's Software
   Inventory Evidence Collection to the SW-PV, which can then pass this
   information on to a central repository such as a Configuration
   Management Database (CMDB) or similar application.  In addition, SW-
   PCs are required to be able to monitor for changes to an endpoint's
   Software Inventory Evidence Collection in near real-time and push
   reports of changes to the SW-PV as soon as those changes are
   detected.  Thus any central repository fed by a SW-PV receiving such



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   information can be updated soon after the change occurs.  Keeping
   such a central repository synchronized with the state of each
   endpoint's Software Inventory Evidence Collection allows tools that
   use this information for their own security activities to make
   decisions in a consistent, efficient manner.

2.1.3.  PA-TNC Use Cases

   Software Message and Attributes for PA-TNC are intended to operate
   over the PA-TNC interface and, as such, are intended to meet the use
   cases set out in the PA-TNC specification.

2.2.  Non-supported Use Cases

   Some use cases not covered by this version of Software Message and
   Attributes for PA-TNC include:

   o  This specification does not address how the endpoint's Software
      Inventory Evidence Collection is populated.  In particular, NEA
      components are not expected to perform software discovery
      activities beyond compiling information in an endpoint's Software
      Inventory Evidence Collection.  This collection might potentially
      come from multiple sources on the endpoint (e.g., information
      generated dynamically by package management tools or discovery
      tools, as well as SWID tag files discovered on the file system).
      While an enterprise might make use of software discovery
      procedures to identify installed software such procedures are
      outside the scope of this specification.

   o  This specification does not address converting inventory
      information expressed in a proprietary format into the standard
      format used in the messages described in this specification.
      Instead, it focuses exclusively on defining interfaces for the
      transportation of software information in the expectation that
      this is the format around which reporting tools will converge.

   o  This specification provides no mechanisms for a posture validator
      to request a specific list of software information based on
      arbitrary software properties.  For example, requesting only
      information about software from a particular vendor is not
      supported.  After the endpoint's software inventory evidence
      collection has been copied to some central location, such as the
      CMDB, processes there can perform queries based on any criteria
      present in the collected information, but this specification does
      not address using such queries to constrain the initial collection
      of this information from the endpoint.





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   o  This specification does not address utilization of properties of
      certain sources of software information that might facilitate
      local tests (i.e., on the endpoint) of endpoint state.  For
      example, the optional package_footprint field of an ISO SWID tag
      can contain a list of files and hash values associated with the
      software indicated by the tag.  Tools on the endpoint can use the
      values in this field to test for the presence of the indicated
      files.  Successful evaluation of such tests leads to greater
      assurance that the indicated software is present on the endpoint.
      Currently, most SWID tag creators do not provide values for tag
      fields that support local testing.  For this reason, the added
      complexity of supporting endpoint testing using these fields is
      out of scope for this specification.  Future versions of this
      specification might add support for such testing.

2.3.  Specification Requirements

   Below are the requirements that the Software Message and Attributes
   for PA-TNC specification is required to meet in order to successfully
   play its role in the NEA architecture.

   o  Efficient

   The NEA architecture enables delay of network access until the
   endpoint is determined not to pose a security threat to the network
   based on its asserted integrity information.  To minimize user
   frustration, the Software Message and Attributes for PA-TNC ought to
   minimize overhead delays and make PA-TNC communications as rapid and
   efficient as possible.

   Efficiency is also important when one considers that some network
   endpoints are small and low powered, some networks are low bandwidth
   and/or high latency, and some transport protocols (such as PT-EAP,
   Posture Transport (PT) Protocol for Extensible Authentication
   Protocol (EAP) Tunnel Methods [RFC7171]) or their underlying carrier
   protocol might allow only one packet in flight at a time or only one
   roundtrip.  However, when the underlying PT protocol imposes fewer
   constraints on communications, this protocol ought to be capable of
   taking advantage of more robust communication channels (e.g. using
   larger messages or multiple roundtrips).

   o  Scalable

   Software Message and Attributes for PA-TNC needs to be usable in
   enterprises that contain tens of thousands of endpoints or more.  As
   such, it needs to allow a security tools to make decisions based on
   up-to-date information about an endpoint's software inventory without
   creating an excessive burden on the enterprise's network.



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   o  Interoperable

   This specification defines the protocol for how PCs and PVs can
   exchange and use software information to provide a NEA Server with
   information about an endpoint's software inventory.  Therefore a key
   goal for this specification is ensuring that all SW PCs and PVs,
   regardless of the vendor who created them, are able to interoperate
   in their performance of these duties.

   o  Support precise and complete historical reporting

   This specification outlines capabilities that support real-time
   understanding of the state of endpoint in a network in a way that can
   be used by other tools.  One means of facilitating such an outcome is
   for a Configuration Management Database (CMDB) to be able to contain
   information about all endpoints connected to the enterprise for all
   points in time between the endpoint's first connection and the
   present.  In such a scenario, it is necessary that any PC be able to
   report any changes to its software inventory evidence collection in
   near real-time while connected and, upon reconnection to the
   enterprise, be able to update the NEA Server (and through it the
   CMDB) with regard to the state of its software inventory evidence
   collection throughout the entire interval when it was not connected.

2.4.  Non-Requirements

   There are certain requirements that the Software Message and
   Attributes for PA-TNC specification explicitly is not required to
   meet.  This list is not exhaustive.

   o  End to End Confidentiality

   This specification does not define mechanism for confidentiality, nor
   is this property automatically provided by PA-TNC interface use.
   Confidentiality is generally provided by the underlying transport
   protocols, such as the PT Binding to TLS [RFC6876] or PT-EAP Posture
   Transport for Tunneled EAP Methods [RFC7171] - see Section 8 for more
   information on related standards.  Should users wish confidentiality
   protection of assessment instructions or results, this needs to be
   provided by parts of the NEA architecture other than this
   specification.

2.5.  Assumptions

   Here are the assumptions that Software Message and Attributes for PA-
   TNC makes about other components in the NEA architecture.

   o  Reliable Message Delivery



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   The Posture Broker Client and Posture Broker Server are assumed to
   provide reliable delivery for PA-TNC messages and therefore the
   Attributes sent between the SW PCs and the PVs.  In the event that
   reliable delivery cannot be provided, the Posture Collector or
   Posture Validator is expected to terminate the connection.

2.6.  Non-Assumptions

   The Software Message and Attributes for PA-TNC specification
   explicitly does not assume:

   o  Authenticity and Accuracy of the Software Inventory Evidence
      Collection with Regard to Endpoint Inventory

   This specification makes no assumption as to whether the software
   information that it reports correctly reflect the software state on
   the endpoint.  This specification does not attempt to detect when the
   endpoint is providing false information, either through malice or
   error, but instead focuses on correctly and reliably providing the
   reported Software Inventory Evidence Collection to the NEA Server.
   Similarly, this specification makes no assumption with regard to the
   completeness of the Software Inventory Evidence Collection's coverage
   of the total set of software installed on the endpoint.  It is
   possible, and even likely, that some installed software is not
   represented by a record in an endpoints Software Inventory Evidence
   Collection.  See Section 6 for more on this security consideration.

2.7.  Software Message and Attributes for PA-TNC Diagram Conventions

   This specification defines the syntax of the Software Message and
   Attributes for PA-TNC using diagrams.  Each diagram depicts the
   format and size of each field in bits.  Implementations MUST send the
   bits in each diagram as they are shown from left to right for each
   32-bit quantity traversing the diagram from top to bottom.  Multi-
   octet fields representing numeric values MUST be sent in network (big
   endian) byte order.

   Descriptions of bit fields (e.g. flags) values refer to the position
   of the bit within the field.  These bit positions are numbered from
   the most significant bit through the least significant bit.  As such,
   an octet with only bit 0 set would have a value of 0x80 (1000 0000),
   an octet with only bit 1 set would have a value of 0x40 (0100 0000),
   and an octet with only bit 7 set would have a value of 0x01 (0000
   0001).







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3.  Software Message and Attributes for PA-TNC System Requirements

   The Software Message and Attributes for PA-TNC specification
   facilitates the exchange of software inventory and event information.
   Specifically, each application supporting Software Message and
   Attributes for PA-TNC includes a component known as the SW-PC that
   receives messages sent with the SW Attributes component type.  The
   SW-PC is also responsible for sending appropriate SW Attributes back
   to the SW-PV in response.  This section outlines what software
   inventories and events are and the requirements on SW-PCs and SW-PVs
   in order to support the stated use cases of this specification.

3.1.  Basic Inventory Exchange

   In the most basic exchange supported by this specification, a SW-PV
   sends a request to the SW-PC requesting all inventory information in
   the endpoint's Software Inventory Evidence Collection.  This simple
   exchange is shown in Figure 2.


       +-------------+                          +--------------+
       |   SW-PC     |                          |    SW-PV     |  Time
       +-------------+                          +--------------+   |
             |                                         |           |
             |<--------------SW Request----------------|           |
             |                                         |           |
             |---------------SW Response-------------->|           |
             |                                         |           V


                    Figure 2: Basic SW Message Exchange

   Upon receiving such a SW Request from the SW-PV, the SW-PC is
   expected to collect all inventory information from the endpoint's
   software evidence collection and place it within its response
   attribute.

   SW-PVs MUST discard without error any SW Response attributes that
   they receive for which they do not know the SW Request parameters
   that led to this SW Response.  This is due to the fact that the SW
   Request includes parameters that control the nature of the response
   (as will be described in the following sections) and without knowing
   those parameters the SW Response cannot be reliably interpreted.
   Most often receiving an unsolicited SW Response attribute happens
   when a NEA Server has multiple SW-PVs; one SW-PV sends a SW Request
   but, unless exclusive delivery is used by the SW-PC in sending the
   response, both SW-PVs receive copies of the resulting SW Response.
   In this case, the SW-PV that didn't send the SW Request would lack



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   the context necessary to correctly interpret the SW Response it
   received and would simply discard it.  Note, however, that
   proprietary measures might allow a SW-PV to discover the SW Request
   parameters for a SW Response even if that SW-PV did not send the
   given SW Request.  As such, there is no blanket requirement for a SW-
   PV to discard all SW Responses to SW Request the SW-PV did not
   generate itself, only that SW-PVs are required to discard SW
   Responses for which they cannot get the necessary context to
   interpret.

   In the case that it is possible to do so, the SW-PC SHOULD send its
   SW Response attribute to the SW-PV that requested it using exclusive
   delivery as described in section 4.5 of RFC 5793 (PB-TNC) [RFC5793].
   Exclusive delivery ensures that only the sender of the SW Request
   receives the resulting SW Response.

3.2.  Software Identifiers

   Software information records contain a large amount of descriptive
   information about installed software products.  However, in many
   cases the complete level of detail in these records is not necessary.
   For example, if one is simply tracking the installation or removal of
   known software products, one only needs enough information to
   recognize the software added or removed.  To allow such uses to be
   efficiently supported, Software Message and Attributes for PA-TNC
   supports the use of Software Identifiers.

   A Software Identifier uniquely identifies a specific version of a
   specific software product.  The Software Message and Attributes for
   PA-TNC specification does not dictate the structure of a Software
   Identifier (beyond stating that it is a string) or define how it is
   created.  Instead, each data model described in the Software Data
   Model IANA table (Section 9.4 includes its own rules for how a
   Software Identifier is created based on a record in the Endpoint's
   Software Inventory Evidence Collection expressed in that data model.
   Within the Software Message and Attributes for PA-TNC specification,
   the Software Identifier is simply an opaque string.

   Software Identifiers allow SW Response messages to identify software
   to a server at a fraction of the bandwidth that would be needed to
   send the entire associated record.  For some combinations of data
   models and sources, the full record might never be necessary as the
   identifier can be directly correlated to the contents of the full
   record.  This is possible with authoritative SWID tags, since these
   tags always have the same contents and thus a Software Identifier
   derived from these tags can be used as a lookup to a local copy of
   the full tag.  For other combinations of source and data model, a
   server might not be able to determine the specific software product



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   and version associated with the identifier without requesting deliver
   of the full record.  In either case, however, a SW-PV can use
   Software Identifiers to track the presence of specific software
   products on an endpoint over time in a bandwidth-efficient manner.

   There are two important limitations of Software Identifiers to keep
   in mind:

      The identifiers do not necessarily change when the associated
      record changes.  In some situations, a record in the endpoint's
      Software Inventory Evidence Collection will change due to new
      information becoming available or in order to correct prior errors
      in that information.  Such changes might or might not result in
      changes to the Software Identifier, depending on the nature of the
      changes and the rules governing how Software Identifiers are
      derived from records of the appropriate data model.

      It is possible that a single software product is installed on a
      single endpoint multiple times.  If both of these installation
      instances are reported by the same source using the same data
      format, then this will result in identical Software Identifiers
      for each installation instances.  In other words, Software
      Identifiers do not uniquely identify installation instances; they
      just uniquely identify software products (which might have more
      than one installation instance).  Instead, to distinguish between
      multiple instances of a single software product, one needs to make
      use of Record Identifiers, described in the following section.

3.2.1.  Record Identifiers

   A Record Identifier is a string generated by the SW-PC that is
   uniquely associated with a specific record within the Endpoint's
   Software Inventory Evidence Collection.  The SW-PC MUST assign a
   unique identifier to each record when it is added to the Endpoint's
   Software Inventory Evidence Collection.  The Record Identifier SHOULD
   remain unchanged if that record is modified.  The SWID-PC might wish
   to assign Record Identifiers sequentially, but any scheme is
   acceptable provided that no two records receive the same identifier.

   Servers can use Record Identifiers to distinguish between multiple
   instances of a single software product installed on an endpoint.
   Since each installation instance of a software product is associated
   with a separate record, servers can use the record identifier to
   distinguish between instances.  For example, if an event is reported
   (as described in Section 3.5), the record identifier will allow the
   server to discern which instance of a software product is involved.





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3.2.2.  Using Software and Record Identifiers in SW Attributes

   A SW Attribute reporting an endpoint's Software Inventory Evidence
   Collection can contain Software Identifiers instead of copies of
   software inventory evidence records.  The message exchange is
   identical to the diagram shown in Figure 2, but the contents of the
   SW Response are Software Identifiers instead of evidence records.
   The SW Request attribute indicates whether the response is required
   to use full records or Software Identifiers.  Using Software
   Identifiers can reduce the attribute size of the response by multiple
   orders of magnitude when compared to sending the same inventory using
   full records.  A SW-PC responds to a SW Request attribute requesting
   Software Identifiers the same way it responds to a request for full
   software records, except that instead of copying each record entirely
   into the attribute body of the response, it provides the specific
   values that comprise a Software Identifier for each record.

   All SW Response attributes include Record Identifiers for each
   reported record.  This is true regardless of whether the record is
   delivered in full or represented by a Software Identifier.

3.3.  Targeted Requests

   Sometimes a SW-PV does not require information about every piece of
   software on an endpoint but only needs to receive updates about
   certain software instances.  For example, enterprise endpoints might
   be required to have certain software products installed and to keep
   these updated.  Instead of requesting a complete inventory just to
   see if these products are present, the SW-PV can make a "targeted
   request" for the software in question.

   Targeted requests follow the same message exchange described in
   Figure 2.  The SW-PV targets its request by providing one or more
   Software Identifiers in its SW Request attribute.  The SW-PC MUST
   then limit its response to contain only records that match the
   indicated Software Identifier(s).  This allows the network exchange
   to exclude information that is not relevant to a given policy
   question, thus reducing unnecessary bandwidth consumption.  The SW-
   PC's response might consist of full records or of Software
   Identifiers, depending on the parameters of the SW Request.

   Note that targeted requests identify the software relevant to the
   request only through Software Identifiers.  This specification does
   not support arbitrary, parameterized querying of records.  For
   example, one cannot request all records from a certain software
   publisher, or all records created by a particular record source.
   Targeted requests only allow a requestor to request specific software




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   (as identified by their Software Identifiers) and receive a response
   that is limited to the named software.

   There is no assumption that a SW-PC will recognize "synonymous
   records" - that is, records from different sources for the same
   software.  Recall that different sources and data models may use
   different Software Identifier strings for the same software product.
   The SW-PC returns only records that match the Software Identifiers in
   the SW Request, even if there might be other records in the
   endpoint's Software Inventory Evidence Collection for the same
   software product.  This is necessary because SW-PCs might not have
   the ability to determine that two Software Identifiers refer to the
   same product.

   Targeted requests do not include Record Identifiers.  The response to
   a targeted request MUST include all records associated with the named
   Software Identifiers, including the case where there are multiple
   records associated with a single Software Identifier.

   SW-PCs MUST accept targeted requests and process them correctly as
   described above.  SW-PVs MUST be capable of making targeted requests
   and processing the responses thereto.

3.4.  Monitoring Changes in an Endpoint's Software Inventory Evidence
      Collection

   The software collection on an endpoint is not static.  As software is
   installed, uninstalled, patched, or updated, the Software Inventory
   Evidence Collection is expected to change to reflect the new software
   state on the endpoint.  Different record sources might update the
   evidence collection at different rates.  For example, a package
   manager might update its records in the Software Inventory Evidence
   Collection immediately whenever it is used to add or remove a
   software product.  By contrast, sources that perform periodic
   examination of the endpoint would likely only update their records in
   the Software Inventory Evidence Collection after each examination.

   All SW-PCs MUST be able to be able to detect changes to the Software
   Inventory Evidence Collection.  Specifically, SW-PCs MUST be able to
   detect:

   o  The creation of records

   o  The deletion of records

   o  The alteration of records





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   An "alteration" is anything that modifies the contents of a record
   (or would modify it, if the record is dynamically generated on
   demand) in any way, regardless of whether the change is functionally
   meaningful.

   SW-PCs MUST detect such changes to the endpoint's Software Inventory
   Evidence Collection in close to real-time (i.e., within seconds) when
   the Posture Collector is operating.  In addition, in the case where
   there is a period during which the SW-PC is not operating, the SW-PC
   MUST be able to determine the net change to the endpoint's Software
   Inventory Evidence Collection over the period it was not operational.
   Specifically, the "net change" represents the difference between the
   state of the endpoint's Software Inventory Evidence Collection when
   the SW-PC was last operational and monitoring its state, and the
   state of the endpoint's software inventory evidence collection when
   the SW-PC resumed operation.  Note that a net change might not
   reflect the total number of change events over this interval.  For
   example, if a record was altered three times during a period when the
   SW-PC was unable to monitor for changes, the net change of this
   interval might only note that there was an alteration to the record,
   but not how many individual alteration events occurred.  It is
   sufficient for a SW-PC's determination of a net change to note that
   there was a difference between the earlier and current state rather
   than enumerating all the individual events that allowed the current
   state to be reached.

   The SW-PC MUST assign a time to each detected change in the
   endpoint's Software Inventory Evidence Collection.  These timestamps
   correspond to the SW-PC's best understanding as to when the detected
   change occurred.  These timestamps MUST be as accurate as possible.
   For changes to the endpoint's Software Inventory Evidence Collection
   that occur while the SW-PC is operating, the SW-PC ought to be able
   to assign a time to the event that is accurate to within a few
   seconds.  For changes to the endpoint's Software Inventory Evidence
   Collection that occur while the SW-PC is not operational, upon
   becoming operational the SW-PC needs to make a best guess as to the
   time of the relevant events (possibly by looking at timestamps on
   files), but these values might be off.  In the case of dynamically
   generated records, the time of change is the time at which the data
   from which the records are generate changes, not the time at which a
   changed record is generated.  For example, if records are dynamically
   generated based on data in an RPM database, the time of change would
   be when the RPM record was changed.

   With regard to deletions of records, the SW-PC needs to detect the
   deletion and MUST retain a copy of the full deleted record along with
   its Record Identifier so that the record itself can be provided to
   the SW-PV upon request.  This copy of the record MUST be retained for



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   a reasonable amount of time.  Vendors and administrators determine
   what "reasonable" means, but a copy of the record SHOULD be retained
   for as long as the event recording the deletion of the record remains
   in the SW-PC's event log (as described in Section 3.5).  This is
   recommended because, as long as the event is in the SW-PC's change
   logs, the SW-PC might send an event attribute (described in
   Section 3.5) that references this record, and a copy of the record is
   needed if the SW-PV wanted a full copy of the relevant records.

   With regard to alterations to a record, SW-PCs MUST detect any
   alterations to the contents of a record.  Alterations need to be
   detected even if they have no functional impact on the record.  A
   good guideline is that any alteration to a record that might change
   the value of a hash taken on the record's contents needs to be
   detected by the SW-PC.  A SW-PC might be unable to distinguish
   modifications to the content of a record from modifications to the
   metadata the file system associates with the record.  For example, a
   SW-PC might use the "last modification" timestamp as an indication of
   alteration to a given record, but a record's last modification time
   can change for reasons other than modifications to the record
   contents.  A SW-PC is still considered compliant with this
   specification if it also reports metadata change events that do not
   change the record itself as alterations to the record.  In other
   words, while SW-PC authors are encouraged to exclude modifications
   that do not affect the bytes within the record, discriminating
   between modifications to file contents and changes to file metadata
   can be difficult and time consuming on some systems.  As such, as
   long as the alterations detected by a SW-PC always cover all
   modifications to the contents of record, the SW-PC is considered
   compliant even if it also registers alterations that do not modify
   the contents of a record as well.  When recording an alteration to a
   record, the SW-PC is only required to note that an alteration
   occurred.  The SW-PC is not required to note or record how the record
   altered, nor is it possible to include such details in SW Attributes
   reporting the change to a SW-PV.

3.5.  Reporting Change Events

   As noted in the preceding section, SW-PCs MUST be able to detect
   changes to the endpoints software inventory evidence collection
   (creation, deletion, and alteration) in near real-time while the SW-
   PC is operational, and MUST be able to account for any net change to
   the endpoint's Software Inventory Evidence Collection that occurs
   when the SW-PC is not operational.  However, to be of use to the
   enterprise, the NEA Server needs to be able to receive these events
   and be able to understand how new changes relate to earlier changes.
   In Software Message and Attributes for PA-TNC, this is facilitated by
   reporting change events.  All SW-PCs MUST be capable of receiving



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   requests for change events and sending change event attributes.  All
   SW-PVs MUST be capable of requesting and receiving change event
   attributes.

3.5.1.  Change Event Records

   A change event record consists of either a complete record or
   Software Identifier from the changed record along with the following
   pieces of information:

   o  The nature of the change (i.e., creation, deletion, or lteration)

   o  An Event Identifier (EID) value

   o  An EID Epoch value

   An EID is a 4-byte unsigned integer that the SW-PC assigns
   sequentially to each observed event (whether detected in real-time or
   deduced by looking for net changes over a period of SW-PC
   inactivity).  All EIDs exist within the context of some "EID Epoch",
   which is also represented as a 4-byte unsigned integer.  EID Epochs
   are used to ensure synchronization between the SW-PC and any SW-PVs
   with which it communicates.  EID Epoch values SHOULD be generated
   randomly and in such a way that it is unlikely that the same EID
   Epoch is generated twice, even if the SW-PC reverted to an earlier
   state (e.g., resetting it to factory defaults).  In the case where a
   SW-PC needs to reset its EID counter, either because it has exhausted
   all available EID values or because the SW-PC's event log becomes
   corrupted, then a new EID Epoch MUST be selected.

   Within an Epoch, EIDs MUST be assigned sequentially, so that if a
   particular event is assigned an EID of N, the next observed event is
   given an EID of N+1.  In some cases, events might occur
   simultaneously, or the SW-PC might not otherwise be able to determine
   an ordering for events.  In these cases, the SW-PC creates an
   arbitrary ordering of the events and assigns EIDs according to this
   ordering.  Two change events MUST NOT ever be assigned the same EID
   within the same EID Epoch.  No meaningful comparison can be made
   between EID values of different Epochs.

   The EID value of 0 is reserved and MUST NOT be associated with any
   event.  Specifically, an EID of 0 in a SW Request attribute indicates
   that a SW-PV wants an inventory response rather than an event
   response, while an EID of 0 in a SW Response is used to indicate the
   initial state of the endpoint's Software Inventory Evidence
   Collection prior to the observation of any events.  Thus the very
   first recorded event in a SW-PC's records within an EID Epoch MUST be
   assigned a value of 1 or greater.  Note that EID and EID Epoch values



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   are assigned by the SW-PC without regard to whether events are being
   reported to one or more SW-PVs.  The SW-PC records events and assigns
   EIDs during its operation.  Any and all SW-PVs that request event
   information from the SW-PC will have those requests served from the
   same event records and thus will see the same EIDs and EID Epochs for
   the same events.

   The SW-PC MUST ensure there is no coverage gap (i.e., change events
   that are not recorded in the SW-PC's records) in its change event
   records.  This is necessary because a coverage gap might give a SW-PV
   a false impression of the endpoint's state.  For example, if a SW-PV
   saw an event indicating that a particular record had been added to
   the endpoint's software inventory evidence collection, and saw no
   subsequent events indicating that record had been deleted, it might
   reasonably assume that this record was still present and thus that
   the indicated software was still installed (assuming the Epoch has
   not changed).  If there is a coverage gap in the SW-PC's event
   records, however, this assumption is false.  For this reason, the SW-
   PC's event records MUST NOT contain gaps.  In the case where there
   are periods where it is possible that changes occurred without the
   SW-PC detecting or recording them, the SW-PC MUST either compute a
   net change and update its event records appropriately, or pick a new
   EID Epoch to indicate a discontinuity with previous event records.

   Within a given Epoch, once a particular event has been assigned an
   EID, this association MUST NOT be changed.  That is, within an Epoch,
   once an EID is assigned to an event, that EID cannot be reassigned to
   a different event, and the event cannot be assigned a different EID.
   When the SW-PC's Epoch changes, all of these associations between
   EIDs and events are cancelled, and EID values once again become free
   for assignment.

3.5.2.  Updating Inventory Knowledge Based on Events

   Modern endpoints can have hundreds of software products installed,
   most of which are unlikely to change from one day to the next.  As
   such, instead of exchanging a complete list of an endpoint's
   inventory on a regular basis, one might wish to only identify changes
   since some earlier known state of this inventory.  This is readily
   facilitated by the use of EIDs to place change events in a context
   relative to earlier state.

   Every inventory sent by a SW-PC to a SW-PV (as described in
   Section 3.1 through Section 3.3) includes the EID Epoch and EID of
   the last event recorded prior to that inventory being compiled.  This
   allows the SW-PV to place all subsequently received event records in
   context relative to this inventory (since the EIDs represent a total
   ordering of all changes to the endpoint's software inventory evidence



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   collection).  Specifically, a SW-PV (or, more likely, a database that
   collects and records its findings) can record an endpoint's full
   inventory and also the EID and Epoch of the most recent event
   reflected in that state.  From that point on, if change events are
   observed, the attribute describing these events indicates the nature
   of the change, the affected records, and the order in which these
   events occurred (as indicated by the sequential EIDs).  Using this
   information, any remote record of the endpoint's Software Inventory
   Evidence Collection can be updated appropriately.

3.5.3.  Using Event Records in SW Attributes

   A SW-PV MUST be able to request a list of event records instead of an
   inventory.  The message flow in such an exchange looks the same as
   the basic flow shown in Figure 2.  The only difference is that, in
   the SW Request attribute, the SW-PV provides an EID other than 0.  (A
   value of 0 in these fields represents a request for an inventory.)
   When the SW-PC receives such a request, instead of identifying
   records from the endpoint's Software Inventory Evidence Collection,
   it consults its list of detected changes.  The SW-PC MUST add an
   event record to the SW Response attribute for each recorded change
   event with an EID greater than or equal to the EID in the SW Request
   attribute (although targeting of requests, as described in the next
   paragraph, might limit this list).  A list of event records MUST only
   contain events with EIDs that all come from the current Epoch.

   SW-PVs can target requests for event records by including one or more
   Software Identifiers, as described in Section 3.3, in the SW Request
   that requests an event record list.  A targeted request for event
   records is used to indicate that only events affecting software that
   match the provided Software Identifiers are to be returned.
   Specifically, in response to a targeted request for event records,
   the SW-PC MUST exclude any event records that are less than the
   indicated EID (within the current EID Epoch) and exclude any event
   records where the affected software does not match one of the
   provided Software Identifiers.  This might mean that the resulting
   list of event records sent in the response attribute does not provide
   a continuous sequence of EIDs.  Both SW-PCs and SWIC-PVs MUST support
   targeted request for event records.

3.5.4.  Partial and Complete Lists of Event Records in SW Attributes

   Over time, a SW-PC might record a large number of change events.  If
   a SW-PV requests all change events covering a large period of time,
   the resulting SW Response attribute might be extremely large,
   especially if the SW-PV is requesting the use of full records instead
   of the use of Software Identifiers (as described in Section 3.2.2).
   In the case that the resulting attribute is too large to send (either



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   because it exceeds the 4GB attribute size limit imposed by the PA-TNC
   specification, or because it exceeds some smaller size limit imposed
   on the SW-PC) the SW-PC MAY send a partial list of event records back
   to the SW-PV.

   Generation of a partial list of events in a SW Response attribute
   requires the SW-PC to identify a "consulted range" of EIDs.  A
   consulted range is the set of event records that are examined for
   inclusion in the SW Response attribute and that are included in that
   attribute if applicable.  Recall that, if a SW Request is targeted,
   only event records that involve the indicated software would be
   applicable.  (See Section 3.3 for more on Targeted Request.)  If a
   request is not targeted, all event records in the considered range
   are applicable and included in the SW Response attribute.

   The lower bound of the consulted range MUST be the EID provided in
   the SW Request.  (Recall that a SW Request indicates a request for
   event records by providing a non-0 EID value in the SW Request.  See
   Section 3.5.3.)  The upper bound of the consulted range is the EID of
   the latest event record (as ordered by EID values) that is included
   in the SW Response attribute if it is applicable to the request.  The
   EID of this last event record is called the "Last Consulted EID".
   The SW-PC chooses this Last Consulted EID based on the size of the
   event record list it is willing to provide to the SW-PV.

   A partial result list MUST include all applicable event records
   within the consulted range.  This means that for any applicable event
   record (i.e., any event record in an un-targeted request, or an event
   record associated with software matching a requested Software
   Identifier in a targeted request) whose EID is greater than or equal
   to the EID provided in the SW Request and whose EID is less than or
   equal to the Last Consulted EID, that event record MUST be included
   in the SW Response conveying this partial list of event records.
   This ensures that every partial list of event records is always
   complete within its indicated range.

   All SW Response attributes that convey event records (either using
   full records or using Software Identifiers) include an Epoch, Last
   EID, and Last Consulted EID field.  The Last EID contains the EID of
   the last event record known to the SW-PC at the time that the SW
   Response attribute was generated.  The Last EID might or might not be
   part of the consulted range.  As noted above, the Last Consulted EID
   field contains the EID of the last event record in the consulted
   range.  The Epoch field contains the EID Epoch associated with the
   Last EID and Last Consulted EID fields as well as all the EIDs in
   event records contained within the SW Response attribute.  Note that,
   if responding to a targeted SW Request, the SW Response attribute
   might not contain the event record whose EID matches the Last



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   Consulted EID value.  For example, the last consulted EID record
   might have been deemed inapplicable because it did not match the
   specified list of Software Identifiers in the SW Request.

   If a SW-PV receives a SW Response attribute where the Last EID and
   Last Consulted EID fields are identical, the SW-PV knows that it has
   received a result list that is complete, given the parameters of the
   request, up to the present time.  On the other hand, if the Last EID
   and Last Consulted EID values differ, the SW-PV has received a
   partial result list.  In the latter case, if the SW-PV wishes to try
   to collect the rest of the partially delivered result list it then
   sends a new SW Request whose EID is one greater than the Last
   Consulted EID in the preceding response.  Doing this causes the SW-PC
   to generate another SW Response attribute containing event records
   where the earliest reported event record is the one immediately after
   the event record with the Last Consulted EID (since EIDs are assigned
   sequentially).  By repeating this process until it receives a SW
   Response where the Last EID and Last Consulted EID are equal, the SW-
   PV is able to collect all event records over a given range, even if
   the complete set of event records would be too large to deliver via a
   single attribute.

   Implementers need to be aware that a SW Request might specify an EID
   that is greater than the EID of the last event recorded by a SW-PC.
   In accordance with the behaviors described in Section 3.5.3, a SW-PC
   MUST respond to such a request with a SW Response attribute of the
   appropriate type (using full records or Software Identifiers as
   specified in the SW Request) that contains zero event records.  This
   is because the SW-PC has recorded no event records with EIDs greater
   than or equal to the EID in the SW Request.  In such a case, the Last
   Consulted EID field MUST be set to the same value as the Last EID
   field in this SW Response attribute.  This case is called out because
   the consulted range on a SW-PC in such a situation is a negative
   range, where the "first" EID in the range (provided in the SW
   Request) is greater than the "last" EID in the range (this being the
   EID of the last recorded event on the SW-PC).  Implementers need to
   ensure that SW-PCs do not experience problems in such a circumstance.

   Note that this specification only supports the returning of partial
   results when returning event records.  There is no way to return a
   partial inventory list under this specification.

3.5.5.  Synchronizing Event Identifiers and Epochs

   Since EIDs are sequential within an Epoch, if a SW-PV's list of event
   records contains gaps in the EID values within a single Epoch, the
   SW-PV knows that there are events that have not been accounted for.
   The SW-PV can either request a new event list to collect the missing



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   events or request a full inventory to re-sync its understanding of
   the state of the Endpoint's Software Inventory Evidence Collection.
   In either case, after the SW-PV's record of the endpoint's Software
   Inventory Evidence Collection has been updated, the SW-PV can record
   the new latest EID value and track events normally from that point
   on.

   If the SW-PV receives any attribute from a SW-PC where the EID Epoch
   differs from the EID Epoch that was used previously, then SW-PV or
   any entity using this information to track the endpoint's Software
   Inventory Evidence Collection knows that there is a discontinuity in
   their understanding of the endpoint's state.  To move past this
   discontinuity and reestablish a current understanding of the state of
   the endpoint's Software Inventory Evidence Collection, the SW-PV
   needs to receive a full inventory from the endpoint.  The SW-PV
   cannot be brought in sync with the endpoint's state through the
   collection of any set of event records in this situation.  This is
   because it is not possible to account for all events on the SW-PC
   over the interval since the previous Epoch was used, because there is
   no way to query for EIDs from a previous Epoch.  Once the SW-PV has
   received a full inventory for the new Epoch, the SW-PV records the
   latest EID reported in this new Epoch and can track further events
   normally.

   A SW-PC MUST NOT report events with EIDs from any Epoch other than
   the current EID Epoch.  The SW-PC MAY choose to purge all event
   records from a previous Epoch from memory after an Epoch change.
   Alternately, the SW-PC MAY choose to retain some event records from a
   previous EID Epoch and assign them new EIDs in the current Epoch.
   However, in the case where a SW-PC chooses the latter option it MUST
   ensure that the order of events according to their EIDs is unchanged
   and that there is no coverage gap between the first retained event
   recorded during the previous Epoch (now reassigned with an EID in the
   current Epoch) and the first event recorded during the current Epoch.
   In particular, the SW-PC MUST ensure that all change events that
   occurred after the last recorded event from the previous Epoch are
   known and recorded.  (This might not be possible if the Epoch change
   is due to state corruption on the SW-PC.)  A SW-PC might choose to
   reassign EIDs to records from a preceding Epoch to create a "sliding
   window" of events, where each Epoch change represents a shift in the
   window of available events.

   In the case where a SW-PC suffers a crash and loses track of its
   current EID Epoch or current EID, then it MUST generate a new EID
   Epoch value and begin assigning EIDs within that Epoch.  In this
   case, the SW-PC MUST purge all event records from before the crash as
   it cannot ensure that there is not a gap between the last of those
   records and the next detected event.  The process for generating a



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   new EID Epoch MUST minimize the possibility that the newly generated
   EID Epoch is the same as a previously used EID Epoch.

   The SW-PV will normally never receive an attribute indicating that
   the latest EID is less than the latest EID reported in a previous
   attribute within the same EID Epoch.  If this occurs, the SW-PC has
   suffered an error of some kind, possibly indicative of at least
   partial corruption of its event log.  In this case, the SW-PV SHOULD
   treat the situation as if there was a change in Epoch and treat any
   local copy of the endpoint's Software Inventory Evidence Collection
   as out-of-sync until a full inventory can be reported by the SW-PC.
   In this case, the SW-PV SHOULD flag the occurrence so the SW-PC can
   be examined to ensure it is now operating properly.

3.6.  Subscriptions

   Thus far, all message exchanges discussed assume that a SW-PV sent an
   SW Request attribute and the SW-PC is providing a direct response to
   that request.  The Software Message and Attributes for PA-TNC
   specification also supports the ability for a SW-PC to send a message
   with a SW Attribute to the SW-PV in response to observed changes in
   the endpoint's software inventory evidence collection, instead of in
   direct response to a SW Request.  An agreement by a SW-PC to send
   content when certain changes are detected to the endpoint's Software
   Inventory Evidence Collection is referred to in this specification as
   a "subscription", and the SW-PV that receives this content is said to
   be "subscribed to" the given SW-PC.  All SW-PCs and SW-PVs MUST
   support the use of subscriptions.

3.6.1.  Establishing Subscriptions

   A SW-PV establishes a subscription on a particular SW-PC by sending a
   SW Request attribute with the Subscription flag set.  The SW Request
   attribute is otherwise identical to the SW Requests discussed in
   previous sections.  Specifically, such a SW Request might request
   full records or Software Identifiers, might be targeted, and might
   request change event records or endpoint inventory.  Assuming no
   error is encountered, a SW-PC MUST send a SW Response attribute in
   direct response to this SW Request attribute, just as if the
   Subscription flag was not set.  As such, the message exchange that
   establishes a new subscription in a SW-PC has the same flow seen in
   the previous message exchanges, as depicted in Figure 2.  If the SW-
   PV does not receive a PA-TNC Error attribute (as described in
   Section 3.8 and Section 4.16) in response to their subscription
   request, the subscription has been successfully established on the
   SW-PC.  The SW Request attribute that establishes a new subscription
   is referred to as the "establishing request" for that subscription.




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   When a subscription is established it is assigned a Subscription ID
   value.  The Subscription ID is equal to the value of the Request ID
   of the establishing request.  (For more about Request IDs, see
   Section 4.8.)

   A SW-PC MUST have the ability to record and support multiple
   simultaneous subscriptions from a single party and from multiple
   parties.  A SW-PV MUST have the ability to record and support
   multiple simultaneous subscriptions to a single party and
   subscriptions to multiple parties.

3.6.2.  Managing Subscriptions

   The SW-PC MUST record each accepted subscription along with the
   identity of the party to whom attributes are to be pushed in
   compliance with the subscription.  This identity includes both the
   NEA Server's connection ID and the Posture Validator Identifier from
   the PB-PA message that delivered the request.

   Likewise, SW-PVs MUST record each accepted subscription for which
   they are the subscribing party along with the associated Subscription
   ID and the identity of the SW-PC that will be fulfilling the
   subscription.  The SW-PV needs to retain this information in order to
   correctly interpret pushed SW Response attributes sent in fulfillment
   of the subscription.  The identity of the SW-PC is given in the
   Posture Collector Identifier of the PB-PA message header in all
   messages from that SW-PC.

3.6.3.  Terminating Subscriptions

   Subscriptions MAY be terminated at any time by the subscribing SW-PV
   by setting the Clear Subscriptions flag in a SW Request.  (See
   Section 4.9 for more on using this flag.)  In the case that a SW
   Request with the Clear Subscriptions flag set is received the SW-PC
   MUST only clear subscriptions that match both the NEA server
   connection ID and the SW-PV ID for this SW Request, and MUST clear
   all such subscriptions.

   This specification does not give the SW-PV the ability to terminate
   subscriptions individually - all subscriptions to the SW-PV are
   cleared when the Clear Subscriptions flag is set.

   This specification does not give the SW-PC the ability to
   unilaterally terminate a subscription.  However, if the SW-PC
   experiences a fatal error fulfilling a subscription, resulting in
   sending a PA-TNC Error attribute of type
   SW_SUBSCRIPTION_FULFILLMENT_ERROR, then the subscription whose
   fulfillment led to the error MUST be treated as terminated by both



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   the SW-PC and the SW-PV.  Only the subscription experiencing the
   error is cancelled and other subscriptions are unaffected.  See
   Section 3.8 for more on this error condition.

   Finally, a subscription is terminated if the connection between the
   SW-PC and SW-PV is deleted.  This occurs when the connection ID used
   in the messages between the SW-PC and the SW-PV becomes unbound.
   Loss of this connection ID would prevent the SW-PC from sending
   messages in fulfillment of this subscription.  As such, loss of the
   connection ID necessarily forces subscription termination between the
   affected parties.

3.6.4.  Subscription Status

   A SW-PV can request that a SW-PC report the list of active
   subscriptions where the SW-PV is the subscriber.  A SW-PV can use
   this to recover lost information about active subscriptions.  A SW-PV
   can also use this capability to verify that a SW-PC has not forgotten
   any of its subscriptions.  The latter is especially useful where a
   SW-PC does not send any attributes in fulfillment of a given
   subscription for a long period of time.  The SW-PV can check the list
   of active subscriptions on the SW-PC and verify whether the
   inactivity is due to a lack of reportable events, or due to the SW-PC
   forgetting its obligations to fulfill a given subscription.

   A SW-PV requests a list of its subscriptions on a given SW-PC by
   sending that SW-PC a Subscription Status Request.  The SW-PC MUST
   then respond with a Subscription Status Response (or a PA-TNC Error
   if an error condition is experienced).  The Subscription Status
   Response MUST contain one subscription record for each of the active
   subscriptions for which the SW-PV is the subscribing party.

3.6.5.  Fulfilling Subscriptions

   As noted in Section 3.4 SW-PCs MUST have the ability to automatically
   detect changes to an endpoint's Software Inventory Evidence
   Collection in near real-time.  For every active subscription, the SW-
   PC MUST send an attribute to the subscribed SW-PV whenever a change
   is detected to relevant records within the endpoint's Software
   Inventory Evidence Collection.  Such an attribute is said to be sent
   "in fulfillment of" the given subscription and any such attribute
   MUST include that subscription's Subscription ID.  If the
   establishing request for that subscription was a targeted request,
   then only records that match the Software Identifiers provided in
   that establishing request are considered relevant.  Otherwise, (i.e.,
   for non-targeted requests) any record is considered relevant for this
   purpose.  Figure 3 shows a sample message exchange where a




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   subscription is established and then later messages are sent from the
   SW-PC in fulfillment of the established subscription.


            +-------------+                    +--------------+
            |   SW-PC     |                    |    SW-PV     |  Time
            +-------------+                    +--------------+   |
                  |                                   |           |
                  |<-----------SW Request-------------|           |
                  |                                   |           |
                  |------------SW Response----------->|           |
                  |                                   |           |
                  .                                   .           .
                  .                                   .           .
                  .                                   .           .
    <Change Event>|                                   |           |
                  |------------SW Response----------->|           |
                  |                                   |           |
                  .                                   .           .
                  .                                   .           .
                  .                                   .           .
    <Change Event>|                                   |           |
                  |------------SW Response----------->|           |
                  |                                   |           V


           Figure 3: Subscription Establishment and Fulfillment

   The contents of an attribute sent in fulfillment of a subscription
   depend on the parameters provided in the establishing request for
   that subscription.  Specifically, the contents of an attribute sent
   in fulfillment of a subscription have the same format as would a
   direct response to the establishing request.  For example, if the
   establishing request stipulated a response that contained an event
   record list wherein affected software indicated using Software
   Identifiers, all attributes sent in fulfillment of this subscription
   will also consist of event record lists expressed using Software
   Identifiers.  As such, all SW Responses displayed in the exchange
   depicted in Figure 3 have the same format.  A SW Response generated
   in fulfillment of an active subscription MUST be a valid SW Response
   attribute according to all the rules outlined in the preceding
   sections.  In other words, an attribute constructed in fulfillment of
   a subscription will look the same as an attribute sent in direct
   response to an explicit request from a SW-PV that had the same
   request parameters and which arrived immediately after the given
   change event.  There are a few special rules that expand on this
   guideline:




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3.6.5.1.  Subscriptions Reporting Inventories

   In the case that a SW-PV subscribes to a SW-PC requesting an
   inventory attribute whenever changes are detected (i.e. the EID in
   the establishing request is 0), then the SW-PC MUST send the
   requested inventory whenever a relevant change is detected.  (A
   "relevant change" is any change for untargeted requests, or a change
   to an indicated record in a targeted request.)  Upon detection of a
   relevant change for an active subscription, the SW-PC sends the
   appropriate inventory information as if it had just received the
   establishing request.  Attributes sent in fulfillment of this
   subscription will probably have a large amount of redundancy, as the
   same records are likely to be present in each of these SW Attributes.
   The role of an inventory subscription is not to report records just
   for the items that changed - that is the role of a subscription that
   reports events (see Section 3.6.5.2).  A SW-PC MUST NOT exclude a
   record from an attribute sent in fulfillment of an inventory
   subscription simply because that record was not involved in the
   triggering event (although a record might be excluded for other
   reasons, such as if the subscription is targeted - see
   Section 3.6.5.3).

3.6.5.2.  Subscriptions Reporting Events

   The way in which a SW-PV indicates it wishes to establish a
   subscription requesting event records is by providing a non-zero EID
   in the SW Request establishing the subscription (see Section 3.5.1).
   However, when the SW-PC constructs an attribute in fulfillment of the
   subscription (other than the direct response to the establishing
   request), it MUST only include event records for the detected
   change(s) that precipitated this response attribute.  In other words,
   it MUST NOT send a complete list of all changes starting with the
   indicated EID, up through the latest change, every time a new event
   is detected.  In effect, the EID in the establishing request is
   treated as being updated every time an attribute is sent in
   fulfillment of this subscription, such that a single event is not
   reported twice in fulfillment of a single subscription.  As such,
   every SW-PC MUST track the EID of the last event that triggered an
   attribute for the given subscription.  When the next event (or set of
   events) is detected, the SW-PC MUST only report events with EIDs
   after the last reported event.  In the case that the EID Epoch of the
   SW-PC changes, the SW-PC MUST treat EID values in the new Epoch as
   being after all EIDs assigned in the previous Epoch regardless of the
   relative numeric values of these EIDs.

   Note that while a subscription is active, the subscribing SW-PV MAY
   make other requests for event records that overlap with events that
   are reported in fulfillment of a subscription.  Such requests are



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   unaffected by the presence of the subscription, nor is the
   subscription affected by such requests.  In other words, a given
   request will get the same results back whether or not there was a
   subscription.  Likewise, an attribute sent in fulfillment of a
   subscription will contain the same information whether or not other
   requests had been received from the SW-PV.

   A SW-PV needs to pay attention to the EID Epoch in these messages, as
   changes in the Epoch might create discontinuities in the SW-PV's
   understanding of the endpoint's Software Inventory Evidence
   Collection state, as discussed in Section 3.5.5.  In particular, once
   the EID Epoch changes, a SW-PV is unable have confidence that it has
   a correct understanding of the state of an endpoint's Software
   Inventory Evidence Collection until after the SW-PV collects a
   complete inventory.

   SW-PCs MAY send partial lists of event records in fulfillment of a
   subscription.  (See Section 3.5.4 for more on partial list of event
   records.)  In the case that a SW-PC sends a partial list of event
   records, it MUST immediately send the next consecutive partial list,
   and continue doing so until it has sent the equivalent of the
   complete list of event records.  In other words, if the SW-PC sends a
   partial list it does not wait for another change event to send
   another SW Response, but continues sending SW Responses until it has
   sent all event records that would have been included in a complete
   fulfillment of the subscription.

3.6.5.3.  Targeted Subscriptions

   Subscriptions MAY be targeted to only apply to records that match a
   given set of Software Identifiers.  In the case where changes are
   detected that affect multiple records, some matching the establishing
   request's Software Identifiers and some not, the attribute sent in
   fulfillment of the subscription MUST only include inventory or events
   (as appropriate) for records that match the establishing request's
   Software Identifiers.  The SW-PC MUST NOT include non-matching
   records in the attribute, even if those non-matching records
   experienced change events that were co-temporal with change events on
   the matching records.

   In addition, a SW-PC MUST send an attribute in fulfillment of a
   targeted subscription only when changes to the endpoint's Software
   Inventory Evidence Collection impact one or more records matching the
   subscription's establishing request's Software Identifiers.  A SW-PC
   MUST NOT send any attribute in fulfillment of a targeted subscription
   based on detected change to the endpoint's Software Inventory
   Evidence Collection that did not involve any of the records targeted
   by that subscription.



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3.6.5.4.  No Subscription Consolidation

   A SW-PV MAY establish multiple subscriptions to a given SW-PC.  If
   this is the case, it is possible that a single change event on the
   endpoint might require fulfillment by multiple subscriptions, and
   that the information included in attributes that fulfill each of
   these subscriptions might overlap.  The SW-PC MUST send separate
   attributes for each established subscription that requires a response
   due to the given event.  Each of these attributes MUST contain all
   information required to fulfill that individual subscription, even if
   that information is also sent in other attributes sent in fulfillment
   of other subscriptions at the same time.  In other words, SW-PCs MUST
   NOT attempt to combine information when fulfilling multiple
   subscriptions simultaneously, even if this results in some redundancy
   in the attributes sent to the SW-PV.

3.6.5.5.  Delayed Subscription Fulfillment

   A SW-PC MAY delay the fulfillment of a subscription following a
   change event in the interest of waiting to see if additional change
   events are forthcoming and, if so, conveying the relevant records
   back to the SW-PV in a single SW Response attribute.  This can help
   reduce network bandwidth consumption between the SW-PC and the SW-PV.
   For example, consider a situation where 10 changes occur a tenth of a
   second apart.  If the SW-PC does not delay in assembling and sending
   SW Response attributes, the SW-PV will receive 10 separate SW
   Response attributes over a period of 1 second.  However, if the SW-PC
   waits half a second after the initial event before assembling a SW
   Response, the SW-PV only receives two SW Response attributes over the
   same period of time.

   Note that the ability to consolidate events for a single subscription
   over a given period of time does not contradict the rules in
   Section 3.6.5.4 prohibiting consolidation across multiple
   subscriptions.  When delaying fulfillment of subscriptions, SW-PCs
   are still required to fulfill each individual subscription
   separately.  Moreover, in the case that change events within the
   delay window cancel each other out (e.g., a record is deleted and
   then re-added), the SW-PC MUST still report each change event rather
   than just reporting the net effect of changes over the delay period.
   In other words, delayed fulfillment can decrease the number of
   attributes send by the SW-PC, but it does not reduce the total number
   of change events reported.

   SW-PCs are not required to support delayed fulfillment of
   subscriptions.  However, in the case that the SW-PC does support
   delayed subscription fulfillment, it MUST be possible to configure
   the SW-PC to disable delayed fulfillment.  In other words, parties



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   deploying SW-PCs need to be allowed to disable delayed subscription
   fulfillment in their SW-PCs.  The manner in which such configuration
   occurs is left to the discretion of implementers, although
   implementers MUST protect the configuration procedure from
   unauthorized tampering.  In other words, there needs to be some
   assurance that unauthorized individuals are not able to introduce
   long delays in subscription fulfillment.

3.7.  Multiple Sources of Software Inventory Evidence Records

   The records in an endpoint's software inventory evidence collection
   might potentially come from multiple sources.  For example, records
   might be derived from ISO SWID tags deposited on the file system and
   collected therefrom.  Records might also be generated by tools such
   as software and package managers (e.g., RPM or YUM) or might be
   translated from software discovery reports.

   A SW-PC is not required to identify every possible source of software
   information on its endpoint.  Some SW-PCs might be explicitly tied
   only to one or a handful of software inventory sources.  For all
   software inventory evidence sources that a particular SW-PC supports,
   it MUST completely support all requirements of this specification
   with regard to those sources.  In other words, for supported sources,
   the SW-PC is required to be capable of providing a complete set of
   the provided software inventory evidence records; monitoring for
   changes in the records reported by those sources, correctly providing
   responses for both full and targeted requests that include records
   from those sources, and providing either complete records or Software
   Identifiers as appropriate.  If the source's output is not in one of
   the data models identified in the Software Data Model IANA table (see
   Section 9.4), the SW-PC MUST be capable of converting that output
   into one of the supported data models.  In all cases, the SW-PC MUST
   also be capable of deriving a Software Identifier from the resulting
   record and also assigning that record a unique Record Identifier.
   The SW-PC MUST NOT provide any inventory or event information from
   software inventory sources for which it cannot provide this full
   support.

   When providing a SW Response (either in direct response to a SW
   Request or in fulfillment of a subscription) the SW-PC MUST include
   the complete set of relevant data from all supported sources of
   software inventory evidence.  In other words, a full inventory is
   required to contain all records from all supported sources, a
   targeted inventory is required to contain all relevant records from
   all sources, and event tracking is required to cover all events from
   all sources.  With regard to events, a SW-PC's assignment of EIDs
   MUST reflect the presence and order of all events on the endpoint (at
   least for supported sources) regardless of the source.  This means



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   that if source A experiences an event, and then source B experiences
   two events, and then source A experiences another two events, the SW-
   PC is required to capture five events with consecutive EID values
   reflecting the order in which the events occur.

   Note that, if a SW-PC collects data from multiple sources, it is
   possible that some software products might be "double counted".  This
   can happen if both sources of inventory evidence provide a record for
   a single installation of a software product.  Moreover, each of these
   provided records might have different Software Identifiers.  When a
   SW-PC reports information or records events from multiple inventory
   evidence sources, it MUST use the information those sources provide,
   rather than attempting to perform some form of reduction.  In other
   words, if multiple sources report records corresponding to a single
   installation of a software product, all such records from each source
   are required to be part of the SW-PC's processing even if this might
   lead to multiple reporting, and the SW-PC is not to ignore some
   records to avoid such multiple reporting.  Similarly, in the case
   that multiple sources report an event, the SW-PC MUST create separate
   event records with separate EIDs for each of these, even if there is
   the chance that they represent the two sources reporting the same
   action on the endpoint.  Entities tracking software inventory
   information collected via SW-PCs and SW-PVs need to be aware that
   such double-reporting might occur.  How (or if) such occurrences are
   detected and resolved is up to the implementers of those entities.

3.8.  Error Handling

   In the case where the SW-PC detects an error in a SW Request
   attribute that it receives it MUST respond with a PA-TNC Error
   attribute with an error code appropriate to the nature of the error.
   (See Section 4.2.8 of PA-TNC [RFC5792] for more details about PA-TNC
   Error attributes and error codes as well as Section 4.16 in this
   specification for error codes specific to SW Attributes.)  In the
   case that an error is detected in a SW Request the SW-PC MUST NOT
   take any action requested by this SW Request, even if partial
   completion of the SW is possible.  In other words, a SW Request that
   contains an error is completely ignored by the SW-PC (beyond sending
   a PA-TNC Error attribute, and possibly logging the error locally)
   rather than being partially executed.

   In the case where the SW-PC receives a valid SW Request attribute but
   experiences an error during the process of responding to that
   attribute's instructions where that error prevents the SW-PC from
   properly or completely fulfilling that request, the SW-PC MUST send a
   PA-TNC Error attribute with an error code appropriate to the nature
   of the error.  In the case where a PA-TNC Error attribute is sent,
   the SW-PC MUST NOT take any of the actions requested by the SW



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   Request attribute which led to the detected error.  This is the case
   even if some actions could have been completed successfully, and
   might even require the SW-PC to reverse some successful actions
   already taken before the error condition was detected.  In other
   words, either all aspects of a SW Request complete fully and
   successfully (in which case the SW-PC sends a SW Response attribute),
   or no aspects of the SW Request occur (in which case the SW-PC sends
   a PA-TNC Error attribute).  In the case that a SW-PC sends a PA-TNC
   Error attribute in response to a SW Request then the SW-PC MUST NOT
   also send any SW Response attribute in response to the same SW
   Request.  For this reason, the sending of a SW Response attribute
   MUST be the last action taken by a SW-PC in response to a SW Request
   to avoid the possibility of a processing error occurring after that
   SW Response attribute is sent.

   In the case that the SW-PC detects an error that prevents it from
   properly or completely fulfilling its obligations under an active
   subscription, the SW-PC MUST send a PA-TNC Error attribute of type
   SW_SUBSCRIPTION_FULFILLMENT_ERROR to the SW-PV that established this
   subscription.  This type of PA-TNC Error attribute identifies the
   specific subscription that cannot be adequately honored due to the
   error condition as well as an error "sub-type".  The error sub-type
   is used to indicate the type of error condition the SW-PC experienced
   that prevented it from honoring the given subscription.  In the case
   that the error condition cannot be identified or does not align with
   any of the defined error codes, the SW_ERROR error code SHOULD be
   used in the sub-type.  In the case that a
   SW_SUBSCRIPTION_FULFILLMENT_ERROR is sent, the associated
   subscription MUST be treated as cancelled by both the SW-PC and SW-
   PV.

   The SW-PV MUST NOT send any PA-TNC Error attributes to SW-PCs.  In
   the case that a SW-PV detects an error condition, it SHOULD log this
   error but does not inform any SW-PC's of this event.  Errors might
   include, but are not limited to, detection of malformed SW Response
   attributes sent from a given SW-PC, as well as detection of error
   conditions when the SW-PV processes SW Responses.

   Both SW-PCs and SW-PVs SHOULD log errors so that administrators can
   trace the causes of errors.  Log messages SHOULD include the type of
   the error, the time it was detected, and additional descriptive
   information to aid in understanding the nature and cause of the
   error.








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4.  Software Message and Attributes for PA-TNC Protocol

   This section describes the format and semantics of the Software
   Message and Attributes for PA-TNC protocol.  Software Message and
   Attributes for PA-TNC uses the standard PA-TNC message header format.
   See the PA-TNC specification [RFC5792] for information on this header
   format.

4.1.  PA Subtype (AKA PA-TNC Component Type)

   The NEA PB-TNC interface provides a general message-batching protocol
   capable of carrying one or more PA-TNC messages between the Posture
   Broker Client and Posture Broker Server.  When PB-TNC is carrying a
   PA-TNC message, the PB-TNC message headers contain a 32 bit
   identifier called the PA Subtype.  The PA Subtype field indicates the
   type of component associated with all of the PA-TNC attributes
   carried by the PB-TNC message.  The core set of PA Subtypes is
   defined in the PA-TNC specification.  This specification adds the
   following enumeration element to the table in section 7.2 of the PA-
   TNC specification [RFC5792] using the IETF Standard name space (SMI
   Private Enterprise Number 0x000000):

   +-----+---------+-------------+-------------------------------------+
   | PEN | Integer | Name        | Defining Specification              |
   +-----+---------+-------------+-------------------------------------+
   | 0   | 9       | SW          | Software Message and Attributes for |
   |     |         | Attributes  | PA-TNC                              |
   +-----+---------+-------------+-------------------------------------+

                            Table 2: PA Subtype

   Each PA-TNC attribute described in this specification is intended to
   be sent between the SW-PC and SW-PV, so will be carried in a PB-TNC
   message indicating a PA Subtype of SW Attributes.  Note that although
   the PA-TNC Error attribute is defined in the PA-TNC specification,
   when it is used in a SW Attribute exchange, it uses the SW Attributes
   Component Definition Value, as described in Section 4.2.8 of the PA-
   TNC specification [RFC5792].  PB-TNC messages MUST always include the
   SW Attributes Subtype defined in this section when carrying SW
   Attributes over PA-TNC.

4.2.  PB-TNC and PA-TNC Messages

   A PA-TNC message is wrapped within a PB-TNC message.  A single PA-TNC
   message might contain one or more PA-TNC attributes.  All of these
   attributes within a single PA-TNC message use the same PA Subtype
   value.  As such, SW Attributes are never sent in the same PA-TNC
   message as attributes defined in other PA-TNC binding specifications.



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   Note, however, that a single PB-TNC batch might contain multiple PB-
   TNC and PA-TNC messages, and each of those messages might use
   different PA Subtypes.

   For more information on PB-TNC and PA-TNC messages and message
   headers, see the PB-TNC [RFC5793] and PA-TNC [RFC5792]
   specifications, respectively.

4.3.  PA-TNC Attribute Header

   The Software Message and Attributes for PA-TNC protocol described in
   this specification is an extension of the PA-TNC protocol described
   in the NEA Architecture.  PA-TNC was designed to be very flexible in
   order to carry many types of PA-TNC attributes that pertain to an
   enumerated set of component types (e.g.  Table 2).  PA-TNC attributes
   might be carried from Posture Collector to Posture Validator or vice
   versa and might carry information about endpoint state or other
   information to be sent between a Posture Validator and a Posture
   Collector.  Therefore, the Software Message and Attributes for PA-TNC
   specification defines a collection of PA-TNC attributes relevant to
   the collection and transmission of software inventories and
   associated events.

   Figure 4, reproduced from the PA-TNC specification, shows the format
   of a PA-TNC attribute.  Multiple PA-TNC attributes can be sent in a
   single PB-TNC message, each housed within an attribute structure as
   described below.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |          PA-TNC Attribute Vendor ID           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    PA-TNC Attribute Type                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    PA-TNC Attribute Length                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Attribute Value (Variable Length)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


               Figure 4: PA-TNC Header and Attribute Format








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   +-----------+-------------------------------------------------------+
   | Field     | Description                                           |
   +-----------+-------------------------------------------------------+
   | Flags     | This field defines flags affecting the processing of  |
   |           | the Software Message and Attributes for PA-TNC.       |
   |           | Permissible flags are given in the PA-TNC             |
   |           | specification. [RFC5792]                              |
   |           |                                                       |
   | Attribute | This field indicates the owner of the name space      |
   | Type      | associated with the Attribute Type.  Attributes       |
   | Vendor ID | defined in the Software Message and Attributes for    |
   |           | PA-TNC specification have a value corresponding to    |
   |           | the IETF SMI Private Enterprise Number value          |
   |           | (0x000000). The PA-TNC Error attribute is defined in  |
   |           | the PA-TNC specification [RFC5792] and also uses the  |
   |           | IETF SMI Private Enterprise Number Value (0x000000).  |
   |           | See Table 4 for more information.                     |
   |           |                                                       |
   | Attribute | This field defines the type of the Attribute. The     |
   | Type      | values corresponding to SW Attributes are given in    |
   |           | Table 4.                                              |
   |           |                                                       |
   | Attribute | This field contains the length in octets of the       |
   | Length    | entire Attribute, including the Attribute's header.   |
   |           |                                                       |
   | Attribute | This field contains the SW Attribute.                 |
   | Value     |                                                       |
   +-----------+-------------------------------------------------------+

              Table 3: Fields of the PA-TNC Attribute Format

4.4.  SW Attribute Overview

   The attributes defined in this specification appear below with a
   short summary of their purposes.  Each attribute is described in
   greater detail in subsequent sections.

   o  SW Request - This attribute is used to request a software
      inventory or software event list from an endpoint.  This attribute
      might also establish a subscription on the recipient SW-PC.  A SW-
      PC MUST NOT send this attribute.

   o  Software Identifier Inventory - This attribute is used to convey
      an inventory expressed using Software Identifiers (instead of full
      records).  When a SW-PC receives a SW Request attribute requesting
      an inventory using Software Identifiers, the SW-PC MUST send a
      Software Identifier Inventory attribute (or a PA-TNC Error) in
      response.  This attribute also MAY be sent by the SW-PC in



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      fulfillment of an active subscription.  A SW-PV MUST NOT send this
      attribute.

   o  Software Identifier Events - This attribute is used to convey a
      list of events concerning changes to an endpoint's Software
      Inventory Evidence Collection.  Affected software inventory
      evidence records are indicated using Software Identifiers (instead
      of full records).  When a SW-PC receives a SW Request attribute
      requesting an event collection using Software Identifiers, the SW-
      PC MUST send a Software Identifier Events attribute (or a PA-TNC
      Error) in response.  This attribute also MAY be sent by the SW-PC
      in fulfillment of an active subscription.  A SW-PV MUST NOT send
      this attribute.

   o  Software Inventory - This attribute is used to convey an inventory
      expressed using full software inventory evidence records (instead
      of Software Identifiers).  When a SW-PC receives a SW Request
      attribute requesting an inventory using full software inventory
      evidence records, the SW-PC MUST send a Software Inventory
      attribute (or a PA-TNC Error) in response.  This attribute also
      MAY be sent by the SW-PC in fulfillment of an active subscription.
      A SW-PV MUST NOT send this attribute.

   o  Software Events - This attribute is used to convey a list of
      events concerning changes to an endpoint's inventory evidence
      collection.  Affected software inventory evidence records are
      indicated using full records (instead of Software Identifiers).
      When a SW-PC receives a SW Request attribute requesting an event
      collection using full records, the SW-PC MUST send a Software
      Events attribute (or a PA-TNC Error) in response.  This attribute
      also MAY be sent by the SW-PC in fulfillment of an active
      subscription.  A SW-PV MUST NOT send this attribute.

   o  Subscription Status Request - This attribute is used to request a
      SW-PC send a summary of all the active subscriptions it has where
      the requesting party is the subscriber.  The SW-PC MUST respond
      with a Subscription Status Response (or a PA-TNC Error).  A SW-PC
      MUST NOT send this attribute.

   o  Subscription Status Response - This attribute is used to convey
      information about the active subscriptions that a SW-PC has for a
      given subscriber.  A SW-PV MUST NOT send this attribute.

   o  PA-TNC Error - This is the standard PA-TNC Error attribute as
      defined in PA-TNC [RFC5792] and is used to indicate that an error
      was encountered during a SW Attribute exchange.  It MUST be sent
      by a SW-PC in response to a SW Request in the case where the SW-PC
      encounters a fatal error (i.e., an error that prevents further



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      processing of an exchange) relating to the attribute exchange.  A
      SW-PV MUST NOT send this attribute.  The SW-PC MUST then ignore
      the erroneous attribute after a PA-TNC Error attribute is sent
      (i.e., do not attempt to act on an attribute that generated a PA-
      TNC Error beyond sending the PA-TNC Error).  In the case where the
      SW-PV experiences a fatal error, it MUST ignore the erroneous
      attribute without sending a PA-TNC Error attribute.  It MAY take
      other actions in response to the error, such as logging the cause
      of the error, or even taking actions to isolate the endpoint

   Because one of the Software Identifier Inventory, Software Identifier
   Events, Software Inventory, or Software Events attributes is expected
   to be sent to a SW-PV in direct response to a SW Request attribute or
   in fulfillment of an active subscription, those four attribute types
   are referred to collectively in this document as "SW Response"
   attributes.

   All SW-PVs MUST be capable of sending SW Requests and be capable of
   receiving and processing all SW Response attributes as well as PA-TNC
   Error attributes.  All SW-PCs MUST be capable of receiving and
   processing SW Requests and be capable of sending all types of SW
   Response attributes as well as PA-TNC Error attributes.  In other
   words, both SW-PVs and SW-PCs are required to support their role in
   exchanges using any of the attribute types defined in this section.
   SW-PVs MUST ignore any SW Request attributes that they receive.  SW-
   PCs MUST ignore any SW Response attributes or PA-TNC Error attributes
   that they receive.

4.5.  SW Attribute Exchanges

   A SW Attribute Exchange is used to provide the SW-PV with a software
   inventory or event collection from the queried endpoint.



















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       +-------------+                      +--------------+
       |   SW-PC     |                      |    SW-PV     |  Time
       +-------------+                      +--------------+   |
             |                                     |           |
             |<------------SW Request--------------|           |
             |                                     |           |
             |             SW Response*            |           |
             |-----------------or----------------->|           |
             |             PA-TNC Error            |           |
             |                                     |           V

     *SW Response is one of the following: Software Identifier
      Inventory, Software Identifier Events, Software Inventory,
      or Software Events.


      Figure 5: SW Attribute Exchange (Direct Response to SW Request)

   In this exchange, the SW-PV indicates to the SW-PC, via a SW Request,
   the nature of the information it wishes to receive (inventory vs.
   events, full or targeted) and how it wishes the returned inventory to
   be expressed (full records or Software Identifiers).  The SW-PC
   responds with the requested information using the appropriate
   attribute type.  A single SW Request MUST only lead to a single SW
   Response or PA-TNC Error that is in direct response to that request.

   In addition, if there is an active subscription on the endpoint, the
   SW-PC sends a SW Response to the SW-PV following a change event on
   the endpoint in fulfillment of that subscription.  Such an exchange
   is shown in Figure 6.


            +-------------+                +--------------+
            |   SW-PC     |                |    SW-PV     |  Time
            +-------------+                +--------------+   |
                  |                               |           |
    <Change Event>|                               |           |
                  |--------SW Response(s)*------->|           |
                  |                               |           |

     *SW Response is one of the following: Software Identifier
      Inventory, Software Identifier Events, Software Inventory,
      or Software Events.


       Figure 6: SW Attribute Exchange (In Fulfillment of an Active
                               Subscription)




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   Note that, unlike direct responses to a SW Request, a single change
   event can precipitate multiple SW Responses for a single
   subscription, but only if all but the last of those SW Responses
   convey partial lists of event records, and the last of those SW
   Responses conveys a complete list of event records.  (That is, the
   initial responses are partial lists and the last response is the
   remainder of the relevant event records, completing the delivery of
   all relevant events at the time of the change event.)  A single
   Change Event MUST NOT be followed by multiple SW Response or PA-TNC
   Error attributes in any combination except as noted earlier in this
   paragraph.

   All SW-PVs and SW-PCs MUST support both types of exchanges.  In
   particular, SW-PCs MUST be capable of pushing a SW Response to a SW-
   PV immediately upon detection of a change to the endpoint's Software
   Inventory Evidence Collection in fulfillment of established SW-PV
   subscriptions, as described in Section 3.6.

4.6.  Software Message and Attributes for PA-TNC Attribute Enumeration

   PA-TNC attribute types are identified in the PA-TNC Attribute Header
   (see Section 4.2) via the Attribute Type Vendor ID and Attribute Type
   fields.  Table 4 identifies the appropriate values for these fields
   for each attribute type used within the Software Message and
   Attributes for PA-TNC protocol.

   +--------------+----------+------------+----------------------------+
   | Attribute    | PEN      | Integer    | Description                |
   | Name         |          |            |                            |
   +--------------+----------+------------+----------------------------+
   | SW Request   | 0x000000 | 0x00000011 | Request from a SW-PV to a  |
   |              |          |            | SW-PC for the SW-PC to     |
   |              |          |            | provide a software         |
   |              |          |            | inventory or event list    |
   |              |          |            |                            |
   | Software     | 0x000000 | 0x00000012 | A collection of Software   |
   | Identifier   |          |            | Identifiers sent from a    |
   | Inventory    |          |            | SW-PC.                     |
   |              |          |            |                            |
   | Software     | 0x000000 | 0x00000013 | A collection of events     |
   | Identifier   |          |            | impacting the endpoint's   |
   | Events       |          |            | Software Inventory         |
   |              |          |            | Evidence Collection, where |
   |              |          |            | impacted software          |
   |              |          |            | inventory evidence records |
   |              |          |            | are indicated using        |
   |              |          |            | Software Identifiers.      |
   |              |          |            |                            |



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   | Software     | 0x000000 | 0x00000014 | A collection of software   |
   | Inventory    |          |            | inventory evidence records |
   |              |          |            | sent from a SW-PC.         |
   |              |          |            |                            |
   | Software     | 0x000000 | 0x00000015 | A collection of events     |
   | Events       |          |            | impacting the endpoint's   |
   |              |          |            | Software Inventory         |
   |              |          |            | Evidence Collection, where |
   |              |          |            | impacted software          |
   |              |          |            | inventory evidence records |
   |              |          |            | are indicated using full   |
   |              |          |            | records.                   |
   |              |          |            |                            |
   | Subscription | 0x000000 | 0x00000016 | A request for a list of a  |
   | Status       |          |            | SW-PV's active             |
   | Request      |          |            | subscription.              |
   |              |          |            |                            |
   | Subscription | 0x000000 | 0x00000017 | A list of a SW-PV's active |
   | Status       |          |            | subscriptions.             |
   | Response     |          |            |                            |
   |              |          |            |                            |
   | Reserved     | 0x000000 | 0x00000018 | These attribute types are  |
   |              |          | -          | reserved for future use in |
   |              |          | 0x0000001F | revisions to Software      |
   |              |          |            | Message and Attributes for |
   |              |          |            | PA-TNC.                    |
   |              |          |            |                            |
   | PA-TNC Error | 0x000000 | 0x00000008 | An error attribute as      |
   |              |          |            | defined in the PA-TNC      |
   |              |          |            | specification [RFC5792].   |
   +--------------+----------+------------+----------------------------+

                     Table 4: SW Attribute Enumeration

4.7.  Normalization of Text Encoding

   In order to ensure consistency of transmitted attributes, a field
   requiring normalization, as indicated in its description, MUST be
   normalized to Network Unicode format as defined in RFC 5198
   [RFC5198].  Network Unicode format defines a refinement of UTF-8 that
   ensures a normalized expression of characters.  SW-PCs and SW-PVs
   MUST NOT perform conversion and normalization on any field values
   except those specifically identified as requiring normalization in
   the following sections.  Note, however, that some data models require
   additional normalization before source information is added to an
   Endpoint's Inventory Evidence Collection as a record.  The references
   from the Software Data Model IANA table (see section Section 9.4 will
   note where this is necessary.



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4.8.  Request IDs

   All SW Request attributes MUST include a Request ID value.  The
   Request ID field provides a value that identifies a given request
   relative to other requests between a SW-PV and the receiving SW-PC.
   Specifically, the SW-PV assigns each SW Request attribute a Request
   ID value that is intended to be unique within the lifetime of a given
   network connection ID as assigned by the SW-PV's Posture Broker
   Server.  In the case where all possible Request ID values have been
   exhausted within the lifetime of a single network connection ID, the
   sender MAY reuse previously used Request IDs within the same network
   connection that are not being used as Subscription IDs.  (See below
   in this section for an explanation of Subscription ID assignment.)
   In this case of Request ID reuse, Request IDs SHOULD be reused in the
   order of their original use.  For example, if a Request ID of X was
   the first Request ID used within a particular network connection and
   if the Request IDs are exhausted, X will be the first reused Request
   ID.  In other words, a SW-PC SHOULD NOT use a given Request ID value
   more than once within a persistent connection between a given Posture
   Broker Client-Posture Broker Server pair, but, in the case where
   reuse is necessary due to exhaustion of possible ID values, the SW-PC
   SHOULD structure the reuse to maximize the time between original and
   subsequent use.  The Request ID value is included in a SW Response
   attribute directly responding to this SW Request to indicate which SW
   Request was received and caused the response.  Request IDs can be
   randomly generated or sequential, as long as values are not repeated
   per the rules in this paragraph.  SW-PCs are not required to check
   for duplicate Request IDs.

   In the case that a SW Request requests the establishment of a
   subscription and the receiving SW-PC agrees to that subscription, the
   Request ID of that SW Request (i.e., the establishing request of the
   subscription) becomes that subscription's Subscription ID.  All
   attributes sent in fulfillment of this subscription include a flag
   indicating that the attribute fulfills a subscription and the
   subscription's Subscription ID.  A SW-PV MUST NOT reuse a Request ID
   value in communicating to a given SW-PC while that Request ID is also
   serving as a Subscription ID for an active subscription with that SW-
   PC.  In the case where a SW-PC receives a SW Request from a given SW-
   PV where that Request ID is also the Subscription ID of an active
   subscription with that SW-PV, the SW-PC MUST respond with a PA-TNC
   Error attribute with an error code of SW_SUBSCRIPTION_ID_REUSE_ERROR.
   Note that this error does not cancel the indicated subscription.

   Subscription Status Requests and Subscription Status Responses do not
   include Request IDs.





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4.9.  SW Request

   A SW-PV sends this attribute to a SW-PC to request that the SW-PC
   send software inventory information to the SW-PV.  A SW-PC MUST NOT
   send this attribute.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags        |       Software Identifier Count               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Request ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Earliest EID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Software Identifier Length  |    Software ID (var length)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



                      Figure 7: SW Request Attribute

   +---------------+---------------------------------------------------+
   | Field         | Description                                       |
   +---------------+---------------------------------------------------+
   | Flags: Bit 0  | If set (1), the SW-PC MUST delete all             |
   | - Clear       | subscriptions established by the requesting SW-PV |
   | Subscriptions | (barring any errors).                             |
   |               |                                                   |
   | Flags: Bit 1  | If set (1), in addition to responding to the      |
   | - Subscribe   | request as described, the SW-PC MUST establish a  |
   |               | subscription with parameters matching those in    |
   |               | the request attribute (barring any errors).       |
   |               |                                                   |
   | Flags: Bit 2  | If unset (0), the SW-PC's response MUST consist   |
   | - Result Type | of complete software inventory evidence records   |
   |               | and thus the response MUST be a Software          |
   |               | Inventory, a Software Events, or a PA-TNC Error   |
   |               | attribute. If set (1), the response MUST consist  |
   |               | of Software Identifiers and thus the response     |
   |               | MUST be a Software Identifier Inventory, a        |
   |               | Software Identifier Events, or a PA-TNC Error     |
   |               | attribute.                                        |
   |               |                                                   |
   | Flags: Bit    | Reserved for future use. This field MUST be set   |
   | 3-7 -         | to zero on transmission and ignored upon          |
   | Reserved      | reception.                                        |



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   |               |                                                   |
   | Software      | A 3-byte unsigned integer indicating the number   |
   | Identifier    | of Software Identifiers that follow. If this      |
   | Count         | value is non-zero, this is a targeted request, as |
   |               | described in Section 3.3.  The Software           |
   |               | Identifier Length and Software ID fields are      |
   |               | repeated, in order, the number of times indicated |
   |               | in this field. In the case where Software         |
   |               | Identifiers are present, the SW-PC MUST only      |
   |               | respond with software inventory evidence records  |
   |               | or Software Identifiers that correspond to the    |
   |               | identifiers the SW-PV provided in this attribute  |
   |               | (or with a PA-TNC Error attribute).  This field   |
   |               | value MAY be 0, in which case there are no        |
   |               | instances of the Software Identifier Length and   |
   |               | Software ID fields. In this case, the SW-PV is    |
   |               | indicating an interest in all software inventory  |
   |               | evidence records on the endpoint (i.e., this is   |
   |               | not a targeted request).                          |
   |               |                                                   |
   | Request ID    | A value that uniquely identifies this SW Request  |
   |               | from a particular SW-PV.                          |
   |               |                                                   |
   | Earliest EID  | In the case where the SW-PV is requesting         |
   |               | software events, this field contains the EID      |
   |               | value of the earliest event the SW-PV wishes to   |
   |               | have reported. (Note - the report will be         |
   |               | inclusive of the event with this EID value.) In   |
   |               | the case where the SW-PV is requesting an         |
   |               | inventory, then this field MUST be 0.             |
   |               | (0x00000000) In the case where this field is non- |
   |               | zero, the SW-PV is requesting events and the SW-  |
   |               | PC MUST respond using a Software Events, Software |
   |               | Identifier Events, or a PA-TNC Error attribute.   |
   |               | In the case where this field is zero, the SW-PV   |
   |               | is requesting an inventory and the SW-PC MUST     |
   |               | respond using a Software Inventory, a Software    |
   |               | Identifier Inventory, or a PA-TNC Error           |
   |               | attribute.                                        |
   |               |                                                   |
   | Software      | A 2-byte unsigned integer indicating the length   |
   | Identifier    | in bytes of the Software ID field.                |
   | Length        |                                                   |
   |               |                                                   |
   | Software ID   | A string containing the Software Identifier value |
   |               | from a software inventory evidence record. This   |
   |               | field value MUST be normalized to Network Unicode |
   |               | format, as described in Section 4.7.  This string |



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   |               | MUST NOT be NULL terminated.                      |
   +---------------+---------------------------------------------------+

                   Table 5: SW Request Attribute Fields

   The SW-PV sends the SW Request attribute to a SW-PC to request the
   indicated information.  Note that between the Result Type flag and
   the Earliest EID field, the SW-PC is constrained to a single possible
   SW Response attribute type (or a PA-TNC Error attribute) in its
   response to the request.

   The Subscribe and Clear Subscription flags are used to manage
   subscriptions for the requesting SW-PV on the receiving SW-PC.
   Specifically, an attribute with the Subscribe flag set seeks to
   establish a new subscription by the requesting SW-PV to the given SW-
   PC, while an attribute with the Clear Subscription flag seeks to
   delete all existing subscriptions by the requesting SW-PV on the
   given SW-PC.  Note that, in the latter case, only the subscriptions
   associated with the Connection ID and the Posture Validator ID of the
   requester are deleted as described in Section 3.6.3.  A newly
   established subscription has the parameters outlined in the Request
   attribute.  Specifically, the Result Type flag indicates the type of
   result to send in fulfillment of the subscription, the value of the
   Earliest EID field indicates whether the fulfillment attributes list
   inventories or events, and the fields describing Software Identifiers
   (if present) indicate if and how a subscription is targeted.  In the
   case that the SW-PC is unable or unwilling to comply with the SW-PV's
   request to establish or clear subscriptions, the SW-PC MUST respond
   with a PA-TNC Error attribute with the SW_SUBSCRIPTION_DENIED_ERROR
   error code.  (Note that if the SW-PV requests that subscriptions be
   cleared but has no existing subscriptions, this is not an error.)

   An attribute requesting the establishment of a subscription is
   effectively doing double-duty, as it is a request for an immediate
   response from the SW-PC in addition to setting up the subscription.
   Assuming the SW-PC is willing to comply with the subscription it MUST
   send an appropriate response attribute to a request with the
   Subscribe flag set containing all requested information.  The same is
   true of the Clear Subscription flag - assuming there is no error the
   SW-PC MUST generate a response attribute without regard to the
   presence of this flag in addition to clearing its subscription list.

   Both the Subscribe and Clear Subscription flags MAY be set in a
   single SW Request attribute.  In the case where this request is
   successful, the end result MUST be equivalent to the SW-PC clearing
   its subscription list for the given SW-PV first and then creating a
   new subscription in accordance with the request parameters.  (In
   other words, do not first create the new subscription and then clear



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   all the subscriptions including the one that was just created.)  In
   the case that the requested actions are successfully completed, the
   SW-PC MUST respond with a SW Response attribute.  (The specific type
   of SW Response attribute depends on the Result Type and Earliest EID
   fields, as described above.)  In the case where there is a failure
   that prevents some part this request from completing, the SW-PC MUST
   NOT add a new subscription, MUST NOT clear the old subscriptions, and
   the SW-PC MUST respond with a PA-TNC Error attribute.  In other
   words, the SW-PC MUST NOT partially succeed at implementing such a
   request; either both actions succeed, or neither succeed.

   The Earliest EID field is used to indicate whether the SW-PV is
   requesting an inventory or event list from the SW-PC.  A value of 0
   (0x00000000) represents a request for inventory information.
   Otherwise, the SW-PV is requesting event information.  For Earliest
   EID values other than 0, the SW-PC's response MUST respond with event
   records, as described in Section 3.5.  Note that the request does not
   identify a particular EID Epoch, since responses can only include
   events in the SW-PC's current EID Epoch.

   The Software Identifier Count indicates the number of Software
   Identifiers in the attribute.  This number might be any value between
   0 and 16,777,216, inclusive.  A single Software Identifier is
   represented by fields: Software Identifier Length and Software ID.
   The Software Identifier Length field indicates the number of bytes
   allocated to Software ID field.  The Software Identifier field
   contains a Software Identifier as describe in Section 3.2.  The
   presence of one or more Software Identifiers is used by the SW-PV to
   indicate a targeted request, which seeks only inventories of or
   events affecting software corresponding to the given identifiers.
   The SW-PC MUST only respond with records that match the Software
   Identifiers provided in the SW-PVs SW Request attribute.

4.10.  Software Identifier Inventory

   A SW-PC sends this attribute to a SW-PV to convey the inventory of
   the endpoint's Software Inventory Evidence Collection expressed using
   Software Identifiers.  This list might represent a complete inventory
   or a targeted list of records, depending on the parameters in the SW-
   PV's request.  A SW-PV MUST NOT send this attribute.  The SW-PC
   either sends this attribute in fulfillment of an existing
   subscription where the establishing request has a Result Type of 1
   and the Earliest EID is zero, or in direct response to a SW Request
   attribute where the Result Type is 1 and the Earliest EID is zero.







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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags        |         Software Identifier Count             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Request ID Copy / Subscription ID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        EID Epoch                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Last EID                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Data Model Type|   Software IdentifierLength   |SW ID (var len)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Record ID Length       |  Record ID (variable length)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



             Figure 8: Software Identifier Inventory Attribute

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Flags: Bit 0 | In the case that this attribute is sent in         |
   | -            | fulfillment of a subscription this bit MUST be set |
   | Subscription | (1).  In the case that this attribute is a direct  |
   | Fulfillment  | response to a SW Request, this bit MUST be unset   |
   |              | (0).                                               |
   |              |                                                    |
   | Flags: Bit   | Reserved for future use. This field MUST be set to |
   | 1-7 -        | zero on transmission and ignored upon reception.   |
   | Reserved     |                                                    |
   |              |                                                    |
   | Software     | The number of Software Identifiers that follow.    |
   | Identifier   | This field is an unsigned integer. The Data Model  |
   | Count        | Type, Software Identifier Length, SW ID, Record ID |
   |              | Length, and Record ID fields are repeated, in      |
   |              | order, the number of times indicated in this       |
   |              | field. This field value MAY be 0, in which case    |
   |              | there are no instances of these fields.            |
   |              |                                                    |
   | Request ID   | In the case where this attribute is in direct      |
   | Copy /       | response to a SW Request attribute from a SW-PV,   |
   | Subscription | this field MUST contain an exact copy of the       |
   | ID           | Request ID field from that SW Request.  In the     |
   |              | case where this attribute is sent in fulfillment   |
   |              | of an active subscription, this field MUST contain |
   |              | the Subscription ID of the subscription being      |



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   |              | fulfilled by this attribute.                       |
   |              |                                                    |
   | EID Epoch    | The EID Epoch of the Last EID value. This field is |
   |              | an unsigned 4-byte integer.                        |
   |              |                                                    |
   | Last EID     | The EID of the last event recorded by the SW-PC,   |
   |              | or 0 if the SW-PC has no recorded events. This     |
   |              | field is an unsigned 4-byte integer.               |
   |              |                                                    |
   | Data Model   | A 1-byte unsigned integer containing an identifier |
   | Type         | number from the Software Data Model IANA table     |
   |              | that identifies the data model of the reported     |
   |              | record.                                            |
   |              |                                                    |
   | Software     | A 2-byte unsigned integer indicating the length in |
   | Identifier   | bytes of the SW ID field.                          |
   | Length       |                                                    |
   |              |                                                    |
   | SW ID        | A string containing the Software Identifier value  |
   |              | from a software inventory evidence record. This    |
   |              | field value MUST be normalized to Network Unicode  |
   |              | format, as described in Section 4.7. This string   |
   |              | MUST NOT be NULL terminated.                       |
   |              |                                                    |
   | Record ID    | A 2-byte unsigned integer indicating the length in |
   | Length       | bytes of the Record ID field.                      |
   |              |                                                    |
   | Record ID    | A string containing the Record Identifier value    |
   |              | from a software inventory evidence record. This    |
   |              | field value MUST be normalized to Network Unicode  |
   |              | format, as described in Section 4.7. This string   |
   |              | MUST NOT be NULL terminated.                       |
   +--------------+----------------------------------------------------+

          Table 6: Software Identifier Inventory Attribute Fields

   In the case that this attribute is sent in fulfillment of a
   subscription, the Subscription Fulfillment bit MUST be set (1).  In
   the case that this attribute is sent in direct response to a SW
   Request, the Subscription Fulfillment bit MUST be unset (0).  Note
   that the SW Response attribute sent in direct response to a SW
   Request that establishes a subscription (i.e., a subscription's
   establishing request) MUST be treated as a direct response to that SW
   Request (and thus the Subscription Fulfillment bit is unset).  SW
   Response attributes are only treated as being in fulfillment of a
   subscription (i.e., Subscription Fulfillment bit set) if they are
   sent following a change event, as shown in Figure 3.




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   The Software Identifier Count field indicates the number of Software
   Identifiers present in this inventory.  Each Software Identifier is
   represented by a set of five fields: Data Model Type, Software
   Identifier Length, SW ID, Record ID Length, and Record ID.  These
   fields will appear once for each reported record.

   When responding directly to a SW Request attribute, the Request ID
   Copy / Subscription ID field MUST contain an exact copy of the
   Request ID field from that SW Request.  When this attribute is sent
   in fulfillment of an existing subscription on this Posture Collector,
   then this field MUST contain the Subscription ID of the fulfilled
   subscription.

   The EID Epoch field indicates the EID Epoch of the Last EID value.
   The Last EID field MUST contain the EID of the last recorded change
   event (see Section 3.5 for more about EIDs and recorded events) at
   the time this inventory was collected.  In the case where there are
   no recorded change events at the time that this inventory was
   collected, this field MUST contain 0.  These fields can be
   interpreted to indicate that the provided inventory (be it full or
   targeted) reflects the record of events on the endpoint after all
   changes up to and including this last event have been accounted for.

4.11.  Software Identifier Events

   A SW-PC sends this attribute to a SW-PV to convey events where the
   affected records are expressed using Software Identifiers.  A SW-PV
   MUST NOT send this attribute.  The SW-PC either sends this attribute
   in fulfillment of an existing subscription where the establishing
   request has a Result Type is 1 and the Earliest EID is non-zero, or
   in direct response to a SW Request attribute where the Result Type is
   1 and the Earliest EID is non-zero.



















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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags        |                Event Count                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Request ID Copy / Subscription ID                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       EID Epoch                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Last EID                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Last Consulted EID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          EID                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Action       |Data Model Type|  Software Identifier Length   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |SW ID (var len)|       Record ID Length        |Record ID (var)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 9: Software Identifier Events Attribute

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Flags: Bit 0 | In the case that this attribute is sent in         |
   | -            | fulfillment of a subscription this bit MUST be set |
   | Subscription | (1).  In the case that this attribute is a direct  |
   | Fulfillment  | response to a SW Request, this bit MUST be unset   |
   |              | (0).                                               |
   |              |                                                    |
   | Flags: Bit   | Reserved for future use. This field MUST be set to |
   | 1-7 -        | zero on transmission and ignored upon reception.   |
   | Reserved     |                                                    |
   |              |                                                    |
   | Event Count  | The number of events that are reported in this     |
   |              | attribute. This field is a 3-byte unsigned         |



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   |              | integer.  The EID, Timestamp, Action, Data Model   |
   |              | Type, Software Identifier Length, SW ID, Record ID |
   |              | Length, and Record ID fields are repeated, in      |
   |              | order, the number of times indicated in this       |
   |              | field. (An instance of these fields is referred to |
   |              | as an "event record" in this attribute.  Thus the  |
   |              | Event Count field indicates the number of event    |
   |              | records.) This field value MAY be 0, in which case |
   |              | there are no instances of these fields.            |
   |              |                                                    |
   | Request ID   | In the case where this attribute is in direct      |
   | Copy /       | response to a SW Request attribute from a SW-PV,   |
   | Subscription | this field MUST contain an exact copy of the       |
   | ID           | Request ID field from that SW Request.  In the     |
   |              | case where this attribute is sent in fulfillment   |
   |              | of an active subscription, this field MUST contain |
   |              | the Subscription ID of the subscription being      |
   |              | fulfilled by this attribute.                       |
   |              |                                                    |
   | EID Epoch    | The EID Epoch of the Last EID value. This field is |
   |              | an unsigned 4-byte integer.                        |
   |              |                                                    |
   | Last EID     | The EID of the last event recorded by the SW-PC,   |
   |              | or 0 if the SW-PC has no recorded events. This     |
   |              | field contains the EID of the SW-PC's last         |
   |              | recorded change event (which might or might not be |
   |              | included as an event record in this attribute).    |
   |              |                                                    |
   | Last         | The EID of the last event record that was          |
   | Consulted    | consulted when generating the event record list    |
   | EID          | included in this attribute. This is different from |
   |              | the Last EID field value if and only if this       |
   |              | attribute is conveying a partial list of event     |
   |              | records. See Section 3.5.4 for more on partial     |
   |              | list of event records.                             |
   |              |                                                    |
   | EID          | The EID of the event in this event record.         |
   |              |                                                    |
   | Timestamp    | The timestamp associated with the event in this    |
   |              | event record. This timestamps is the SW-PC's best  |
   |              | understanding of when the given event occurred.    |
   |              | Note that this timestamp might be an estimate.     |
   |              | The Timestamp date and time MUST be represented as |
   |              | an RFC 3339 [5] compliant ASCII string in          |
   |              | Coordinated Universal Time (UTC) time with the     |
   |              | additional restrictions that the 'T' delimiter and |
   |              | the 'Z' suffix MUST be capitalized and fractional  |
   |              | seconds (time-secfrac) MUST NOT be included. This  |



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   |              | field conforms to the date-time ABNF production    |
   |              | from section 5.6 of RFC 3339 [RFC3339] with the    |
   |              | above restrictions.  Leap seconds are permitted    |
   |              | and SW-PVs MUST support them.  The Timestamp       |
   |              | string MUST NOT be NULL terminated or padded in    |
   |              | any way. The length of this field is always 20     |
   |              | octets.                                            |
   |              |                                                    |
   | Action       | The type of event that is recorded in this event   |
   |              | record. Possible values are: 1 = CREATION - the    |
   |              | addition of a record to the endpoint's Software    |
   |              | Inventory Evidence Collection; 2 = DELETION - the  |
   |              | removal of a record from the endpoint's Software   |
   |              | Inventory Evidence Collection; 3 = ALTERATION -    |
   |              | There was an alteration to a record within the     |
   |              | endpoint's Software Inventory Evidence Collection. |
   |              | All other values are reserved for future use and   |
   |              | MUST NOT be used when sending attributes. In the   |
   |              | case where a SW-PV receives an event record that   |
   |              | uses an action value other than the ones defined   |
   |              | here, it MUST ignore that event record but SHOULD  |
   |              | process other event records in this attribute as   |
   |              | normal.                                            |
   |              |                                                    |
   | Data Model   | A 1-byte unsigned integer containing an identifier |
   | Type         | number from the Software Data Model IANA table     |
   |              | that identifies the data model of the reported     |
   |              | record.                                            |
   |              |                                                    |
   | Software     | A 2-byte unsigned integer indicating the length in |
   | Identifier   | bytes of the SW ID field.                          |
   | Length       |                                                    |
   |              |                                                    |
   | SW ID        | A string containing the Software Identifier value  |
   |              | from a software inventory evidence record. This    |
   |              | field value MUST be normalized to Network Unicode  |
   |              | format, as described in Section 4.7. This string   |
   |              | MUST NOT be NULL terminated.                       |
   |              |                                                    |
   | Record ID    | A 2-byte unsigned integer indicating the length in |
   | Length       | bytes of the Record ID field.                      |
   |              |                                                    |
   | Record ID    | A string containing the Record Identifier value    |
   |              | from a software inventory evidence record. This    |
   |              | field value MUST be normalized to Network Unicode  |
   |              | format, as described in Section 4.7. This string   |
   |              | MUST NOT be NULL terminated.                       |
   +--------------+----------------------------------------------------+



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           Table 7: Software Identifier Events Attribute Fields

   The first few fields in the Software Identifier Events attribute
   mirror those in the Software Identifier Inventory attribute.  The
   primary difference is that, instead of conveying an inventory using
   Software Identifiers, the attribute conveys zero or more event
   records, consisting of the EID, timestamp, action type, data model
   type, Software Identifier, and Record Identifier of the affected
   software inventory evidence record.

   With regard to the Timestamp field, it is important to note that
   clock skew between the SW-PC and SW-PV as well as between different
   SW-PCs within an enterprise might make correlation of timestamp
   values difficult.  This specification does not attempt to resolve
   clock skew issues, although other mechanisms outside of this
   specification do exist to reduce the impact of clock skew and make
   the timestamp more useful for such correlation.  Instead, Software
   Message and Attributes for PA-TNC uses Timestamp value primarily as a
   means to indicate the amount of time between two events on a single
   endpoint.  For example, by taking the difference of the times for
   when a record was removed and then subsequently re-added, one can get
   an indication as to how long the system was without the given record
   (and, thus without the associated software).  Since this will involve
   comparison of timestamp values all originating on the same system,
   clock skew between the SW-PC and SW-PV is not an issue.  However, if
   the SW-PC's clock was adjusted between two recorded events, it is
   possible for such a calculation to lead to incorrect understandings
   of the temporal distance between events.  Users of this field need to
   be aware of the possibility for such occurrences.  In the case where
   the Timestamp values of two events appear to contradict the EID
   ordering of those events (i.e., the later EID has an earlier
   timestamp) the recipient MUST treat the EID ordering as correct.

   All event records in a Software Identifier Events Attribute are
   required to be part of the same EID Epoch.  Specifically, all
   reported events MUST have an EID from the same EID Epoch as each
   other, and which is the same as the EID Epoch of the Last EID and
   Last Consulted EID values.  The SW-PC MUST NOT report events with
   EIDs from different EID Epochs.

   The Last Consulted EID field contains the EID of the last event
   record considered for inclusion in this attribute.  If this attribute
   contains a partial event set (as described in Section 3.5.4) this
   field value will differ from that of the Last EID field; if this
   attribute contains a complete event set, the Last EID and Last
   Consulted EID values are identical.





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   If multiple events are sent in a Software Identifier Events
   attribute, the order in which they appear within the attribute is not
   significant.  The EIDs associated with them are used for ordering the
   indicated events appropriately.  Also note that a single Software
   Identifier might appear multiple times in an attribute, such as if
   multiple events involving the associated record were being reported.

4.12.  Software Inventory

   A SW-PC sends this attribute to a SW-PV to convey a list of inventory
   records.  A SW-PV MUST NOT send this attribute.  The SW-PC either
   sends this attribute in fulfillment of an existing subscription where
   the establishing request had a Result Type of 0 and the Earliest EID
   is zero, or in direct response to a SW Request attribute where the
   Result Type is 0 and the Earliest EID is zero.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Flags         |             Record Count                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Request ID Copy / Subscription ID              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            EID Epoch                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Last EID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Data Model Type|        Record ID Length       |Record ID (var)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Record Length                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Record (Variable)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 10: Software Inventory Attribute

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Flags: Bit 0 | In the case that this attribute is sent in         |
   | -            | fulfillment of a subscription this bit MUST be set |
   | Subscription | (1).  In the case that this attribute is a direct  |
   | Fulfillment  | response to a SW Request, this bit MUST be unset   |
   |              | (0).                                               |
   |              |                                                    |
   | Flags: Bit   | Reserved for future use. This field MUST be set to |



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   | 1-7 -        | zero on transmission and ignored upon reception.   |
   | Reserved     |                                                    |
   |              |                                                    |
   | Record Count | The number of records that follow. This field is a |
   |              | 3-byte unsigned integer. The Data Model Type,      |
   |              | Record Identifier Length, Record ID, Record        |
   |              | Length, and Record fields are repeated, in order,  |
   |              | the number of times indicated in this field. This  |
   |              | field value MAY be 0 in which case there are no    |
   |              | instances of these fields.                         |
   |              |                                                    |
   | Request ID   | In the case where this attribute is in direct      |
   | Copy /       | response to a SW Request attribute from a SW-PV,   |
   | Subscription | this field MUST contain an exact copy of the       |
   | ID           | Request ID field from that SW Request.  In the     |
   |              | case where this attribute is sent in fulfillment   |
   |              | of an active subscription, this field MUST contain |
   |              | the Subscription ID of the subscription being      |
   |              | fulfilled by this attribute.                       |
   |              |                                                    |
   | EID Epoch    | The EID Epoch of the Last EID value. This field is |
   |              | an unsigned 4-byte integer.                        |
   |              |                                                    |
   | Last EID     | The EID of the last event recorded by the SW-PC,   |
   |              | or 0 if the SW-PC has no recorded events. This     |
   |              | field is an unsigned 4-byte integer.               |
   |              |                                                    |
   | Data Model   | A 1-byte unsigned integer containing an identifier |
   | Type         | number from the Software Data Model IANA table     |
   |              | that identifies the data model of the reported     |
   |              | record.                                            |
   |              |                                                    |
   | Record ID    | A 2-byte unsigned integer indicating the length in |
   | Length       | bytes of the Record ID field.                      |
   |              |                                                    |
   | Record ID    | A string containing the Record Identifier value    |
   |              | from a software inventory evidence record. This    |
   |              | field value MUST be normalized to Network Unicode  |
   |              | format, as described in Section 4.7. This string   |
   |              | MUST NOT be NULL terminated.                       |
   |              |                                                    |
   | Record Len   | This is a 4-byte unsigned integer indicating the   |
   |              | length of the following software inventory         |
   |              | evidence record in bytes.                          |
   |              |                                                    |
   | Record       | A software inventory evidence record as a string.  |
   |              | The record MUST be converted and normalized to     |
   |              | Network Unicode format, as described in Section    |



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   |              | 4.7. This string MUST NOT be NULL terminated.      |
   +--------------+----------------------------------------------------+

               Table 8: Software Inventory Attribute Fields

   The Software Inventory attribute contains some number of software
   inventory evidence records.  Given that the size of records can vary
   considerably, the length of this attribute is highly variable and, if
   transmitting a complete inventory, can be extremely large.
   Enterprises might wish to constrain the use of Software Inventory
   attributes to targeted requests to avoid over-burdening the network
   unnecessarily.

   When copying a software inventory evidence record into the Record
   field, the record MUST be converted and normalized to use Network
   Unicode format prior to its inclusion in the record field.

4.13.  Software Events

   A SW-PC sends this attribute to a SW-PV to convey a list of events
   where the affected software inventory evidence records are expressed
   using full records.  A SW-PV MUST NOT send this attribute.  The SW-PC
   either sends this attribute in fulfillment of an existing
   subscription where the establishing request has a Result Type of 0
   and the Earliest EID is non-zero, or in direct response to a SW
   Request attribute where the Result Type is 0 and the Earliest EID is
   non-zero.

   Note that each record is reported along with its Record Identifier.
   This can be used to link reported records to reported Software
   Identifier + Record Identifier pairs.




















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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Flags       |                  Event Count                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Request ID Copy / Subscription ID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           EID Epoch                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Last EID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Last Consulted EID                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               EID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Action   |Data Model Type|      Record ID Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Record Identifier (Variable Length)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Record Len                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Record (Variable Length)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 11: Software Events Attribute

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Flags: Bit 0 | In the case that this attribute is sent in         |
   | -            | fulfillment of a subscription this bit MUST be set |
   | Subscription | (1).  In the case that this attribute is a direct  |
   | Fulfillment  | response to a SW Request, this bit MUST be unset   |
   |              | (0).                                               |
   |              |                                                    |
   | Flags: Bit   | Reserved for future use. This field MUST be set to |
   | 1-7 -        | zero on transmission and ignored upon reception.   |



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   | Reserved     |                                                    |
   |              |                                                    |
   | Event Count  | The number of events being reported in this        |
   |              | attribute. This field is a 3-byte unsigned         |
   |              | integer.  The EID, Timestamp, Action, Data Model   |
   |              | Type, Record Identifier Length, Record Identifier, |
   |              | Record Length, and Record fields are repeated, in  |
   |              | order, the number of times indicated in this       |
   |              | field. (An instance of these fields is referred to |
   |              | as an "event record" in this attribute. Thus the   |
   |              | Event Count field indicates the number of event    |
   |              | records.) This field value MAY be 0, in which case |
   |              | there are no instances of these fields.            |
   |              |                                                    |
   | Request ID   | In the case where this attribute is in direct      |
   | Copy /       | response to a SW Request attribute from a SW-PV,   |
   | Subscription | this field MUST contain an exact copy of the       |
   | ID           | Request ID field from that SW Request.  In the     |
   |              | case where this attribute is sent in fulfillment   |
   |              | of an active subscription, this field MUST contain |
   |              | the Subscription ID of the subscription being      |
   |              | fulfilled by this attribute.                       |
   |              |                                                    |
   | EID Epoch    | The EID Epoch of the Last EID value. This field is |
   |              | an unsigned 4-byte integer.                        |
   |              |                                                    |
   | Last EID     | The EID of the last event recorded by the SW-PC,   |
   |              | or 0 if the SW-PC has no recorded events. This     |
   |              | field contains the EID of the SW-PC's last         |
   |              | recorded change event (which might or might not be |
   |              | included as an event record in this attribute).    |
   |              |                                                    |
   | Last         | The EID of the last event record that was          |
   | Consulted    | consulted when generating the event record list    |
   | EID          | included in this attribute. This is different from |
   |              | the Last EID field value if and only if this       |
   |              | attribute is conveying a partial list of event     |
   |              | records. See Section 3.5.4 for more on partial     |
   |              | list of event records.                             |
   |              |                                                    |
   | EID          | The EID of the event in this event record.         |
   |              |                                                    |
   | Timestamp    | The timestamp associated with the event in this    |
   |              | event record. This timestamp is the SW-PC's best   |
   |              | understanding of when the given event occurred.    |
   |              | Note that this timestamp might be an estimate.     |
   |              | The Timestamp date and time MUST be represented as |
   |              | an RFC 3339 [5] compliant ASCII string in          |



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   |              | Coordinated Universal Time (UTC) time with the     |
   |              | additional restrictions that the 'T' delimiter and |
   |              | the 'Z' suffix MUST be capitalized and fractional  |
   |              | seconds (time-secfrac) MUST NOT be included. This  |
   |              | field conforms to the date-time ABNF production    |
   |              | from section 5.6 of RFC 3339 [RFC3339] with the    |
   |              | above restrictions.  Leap seconds are permitted    |
   |              | and SW-PVs MUST support them.  The Timestamp       |
   |              | string MUST NOT be NULL terminated or padded in    |
   |              | any way. The length of this field is always 20     |
   |              | octets.                                            |
   |              |                                                    |
   | Action       | The type of event that is recorded in this event   |
   |              | record. Possible values are: 1 = CREATION - the    |
   |              | addition of a record to the endpoint's Software    |
   |              | Inventory Evidence Collection; 2 = DELETION - the  |
   |              | removal of a record from the endpoint's Software   |
   |              | Inventory Evidence Collection; 3 = ALTERATION -    |
   |              | There was an alteration to a record within the     |
   |              | endpoint's Software Inventory Evidence Collection. |
   |              | All other values are reserved for future use and   |
   |              | MUST NOT be used when sending attributes. In the   |
   |              | case where a SW-PV receives an event record that   |
   |              | uses an action value other than the ones defined   |
   |              | here, it MUST ignore that event record but SHOULD  |
   |              | process other event records in this attribute as   |
   |              | normal.                                            |
   |              |                                                    |
   | Data Model   | A 1-byte unsigned integer containing an identifier |
   | Type         | number from the Software Data Model IANA table     |
   |              | that identifies the data model of the reported     |
   |              | record.                                            |
   |              |                                                    |
   | Record ID    | A 2-byte unsigned integer indicating the length in |
   | Length       | bytes of the Record ID field.                      |
   |              |                                                    |
   | Record ID    | A string containing the Record Identifier value    |
   |              | from a software inventory evidence record. This    |
   |              | field value MUST be normalized to Network Unicode  |
   |              | format, as described in Section 4.7. This string   |
   |              | MUST NOT be NULL terminated.                       |
   |              |                                                    |
   | Record Len   | This is a 4-byte unsigned integer indicating the   |
   |              | length of the following record in bytes.           |
   |              |                                                    |
   | Record       | A software inventory evidence record as a string.  |
   |              | The record MUST be converted and normalized to     |
   |              | Network Unicode format, as described in Section    |



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   |              | 4.7. This string MUST NOT be NULL terminated.      |
   +--------------+----------------------------------------------------+

                 Table 9: Software Events Attribute Fields

   The fields of this attribute are used in the same way as the
   corresponding fields of the previous attributes.  As with the
   Software Inventory attribute, a Software Events attribute can be
   quite large if many events have occurred following the event
   indicated by a request's Earliest EID.  As such, it is recommended
   that the SW Request attributes only request full records be sent
   (Result Type set to 0) in a targeted request, thus constraining the
   response just to records that match a given set of Software
   Identifiers.

   As with the Software Identifier Events Attribute, this attribute MUST
   only contain event records with EIDs coming from the current EID
   Epoch of the SW-PC.

   As with the Software Inventory Attribute, the SW-PC MUST perform
   conversion and normalization of the record.

4.14.  Subscription Status Request

   A SW-PV sends this attribute to a SW-PC to request a list of active
   subscriptions for which the requesting SW-PV is the subscriber.  A
   SW-PC MUST NOT send this attribute.

   This attribute has no fields.

   A SW-PC MUST respond to this attribute by sending a Subscription
   Status Response attribute (or a PA-TNC Error attribute if it is
   unable to correctly provide a response).

4.15.  Subscription Status Response

   A SW-PC sends this attribute to a SW-PV to report the list of active
   subscriptions for which the receiving SW-PV is the subscriber.  A SW-
   PV MUST NOT send this attribute.












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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Status Flags  |            Subscription Record Count          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Flags         |          Software Identifier Count            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Request ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Earliest EID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Software Identifier Length   |    Software ID (var length)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 12: Subscription Status Response Attribute

   +-----------------+-------------------------------------------------+
   | Field           | Description                                     |
   +-----------------+-------------------------------------------------+
   | Flags: Bit 0-7  | Reserved for future use. This field MUST be set |
   | - Reserved      | to zero on transmission and ignored upon        |
   |                 | reception.                                      |
   |                 |                                                 |
   | Subscription    | The number of subscription records that follow. |
   | Record Count    | This field is a 3-byte unsigned integer.  The   |
   |                 | Flags, Software Identifier Count, Request ID,   |
   |                 | Earliest EID, Software Identifier Length, and   |
   |                 | Software ID fields are repeated, in order, the  |
   |                 | number of times indicated in this field. This   |
   |                 | field value MAY be 0 in which case there are no |
   |                 | instances of these fields.                      |
   |                 |                                                 |
   | Flags, Software | For each active subscription, these fields      |
   | Identifier      | contain an exact copy of the fields with the    |
   | Count, Request  | same name as provided in the subscription's     |
   | ID, Earliest    | establishing request.                           |
   | EID, Software   |                                                 |
   | Identifier      |                                                 |
   | Length, and     |                                                 |
   | Software ID     |                                                 |
   +-----------------+-------------------------------------------------+

               Table 10: Subscription Status Response Fields

   A Subscription Status Response contains zero or more subscription
   records.  Specifically, it MUST contain one subscription record for
   each active subscription associated with the party that sent the



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   Subscription Status Request to which this attribute is a response.
   As described in Section 3.6.2, the SW-PC MUST use the requester's
   Connection ID and its Posture Validator ID to determine which
   subscriptions are associated with the requester.

   A SW-PC MUST send a Subscription Status Response attribute in
   response to a Subscription Status Request attribute.  The only
   exception to this is if the SW-PC experiences an error condition that
   prevents it from correctly populating the Subscription Status
   Response attribute, in which case it MUST respond with a PA-TNC Error
   attribute appropriate to the type of error experienced.  If there are
   no active subscriptions associated with the requesting party, the
   Subscription Status Response attribute will consist of its Status
   Flags field, a Subscription Record Count field with a value of 0, and
   no additional fields.

   Each subscription record included in a Subscription Status Response
   attribute duplicates the fields of a SW Request attribute that was
   the establishing request of a subscription.  Note that the Request ID
   field in the record captures the Subscription ID associated with the
   given subscription record (since the Subscription ID is the same as
   the Request ID of the establishing request).  Note also that if the
   establishing request is targeted, then its Record Count field will be
   non-zero and, within that subscription record, the Record Namespace
   Length, Record Namespace, Record ID Length, and Record ID fields are
   repeated, in order, the number of times indicated in the Record Count
   field.  As such, each subscription record can be different sizes.  If
   the establishing request is not targeted (Record Count field is 0),
   the subscription record has no Record Namespace Length, Record
   Namespace, Record ID Length, or Record ID fields.

   When a SW-PV compares the information received in a Subscription
   Status Response to its own records of active subscriptions it should
   be aware that the SW-PC might be unable to distinguish this SW-PV
   from other SW-PVs on the same NEA Server.  As a result, it is
   possible that the SW-PC will report more subscription records than
   the SW-PV recognizes.  For this reason, SW-PVs SHOULD NOT
   automatically assume that extra subscriptions reported in a
   Subscription Status Response indicate a problem.

4.16.  PA-TNC Error as Used by Software Message and Attributes for PA-
       TNC

   The PA-TNC Error attribute is defined in the PA-TNC specification
   [RFC5792], and its use here conforms to that specification.  A PA-TNC
   Error can be sent due to any error in the PA-TNC exchange and might
   also be sent in response to error conditions specific to the Software




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   Message and Attributes for PA-TNC exchange.  The latter case utilizes
   error codes defined below.

   A PA-TNC Error attribute is sent instead of a SW Response attribute
   due to factors that prevent the reliable creation of a SW Response.
   As such, a SW-PC MUST NOT send both a PA-TNC Error attribute and a SW
   Response attribute in response to a single SW Request attribute.

   Table 11 lists the Error Code values for the PA-TNC Error attribute
   specific to the Software Message and Attributes for PA-TNC exchange.
   In all of these cases, the Error Code Vendor ID field MUST be set to
   0x000000, corresponding to the IETF SMI Private Enterprise Number.
   The Error Information structures for each error type are described in
   the following subsections.

   Note that a message with a Software Message and Attributes for PA-TNC
   attribute might also result in an error condition covered by the
   Standard PA-TNC Error Codes defined in PA-TNC.  For example, a SW
   Attribute might have an invalid parameter, leading to an error code
   of "Invalid Parameter".  In this case, the SW-PC MUST use the
   appropriate PA-TNC Error Code value as defined in Section 4.2.8 of
   PA-TNC specification.

   +-----------------------+-------------------------------------------+
   | Error Code Value      | Description                               |
   +-----------------------+-------------------------------------------+
   | 0x00000020            | SW_ERROR. This indicates a fatal error    |
   |                       | (i.e., an error that precludes the        |
   |                       | creation of a suitable response           |
   |                       | attribute) other than the errors          |
   |                       | described below but still specific to the |
   |                       | processing of SW Attributes. The          |
   |                       | Description field SHOULD contain          |
   |                       | additional diagnostic information.        |
   |                       |                                           |
   | 0x00000021            | SW_SUBSCRIPTION_DENIED_ERROR. This        |
   |                       | indicates that the SW-PC denied the SW-   |
   |                       | PV's request to establish a subscription. |
   |                       | The Description field SHOULD contain      |
   |                       | additional diagnostic information.        |
   |                       |                                           |
   | 0x00000022            | SW_RESPONSE_TOO_LARGE_ERROR. This         |
   |                       | indicates that the SW-PC's response to    |
   |                       | the SW-PV's request was too large to be   |
   |                       | serviced. The error information structure |
   |                       | indicates the largest possible size of a  |
   |                       | response supported by the SW-PC (see      |
   |                       | Section 4.16.2).  The Description field   |



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   |                       | SHOULD contain additional diagnostic      |
   |                       | information.                              |
   |                       |                                           |
   | 0x00000023            | SW_SUBSCRIPTION_FULFILLMENT_ERROR. This   |
   |                       | indicates that the SW-PC experienced an   |
   |                       | error fulfilling a given subscription.    |
   |                       | The error information includes the        |
   |                       | Subscription ID of the relevant           |
   |                       | subscription, as well as a sub-error that |
   |                       | describes the nature of the error the SW- |
   |                       | PC experienced. The SW-PC and SW-PV MUST  |
   |                       | treat the identified subscription as      |
   |                       | cancelled.                                |
   |                       |                                           |
   | 0x00000024            | SW_SUBSCRIPTION_ID_REUSE_ERROR. This      |
   |                       | indicates that the SW-PC received a SW    |
   |                       | Request from a given SW-PV where the      |
   |                       | Request ID of that SW Request is          |
   |                       | currently used as the Subscription ID of  |
   |                       | an active subscription with that SW-PV.   |
   |                       | This error does not cancel the identified |
   |                       | subscription.                             |
   |                       |                                           |
   | 0x00000025-0x0000002F | RESERVED. These Error Codes are reserved  |
   |                       | for use by future revisions of the        |
   |                       | Software Message and Attributes for PA-   |
   |                       | TNC specification. Any PA-TNC Error       |
   |                       | attribute using one of these Error Codes  |
   |                       | MUST be treated as indicating a fatal     |
   |                       | error on the sender without further       |
   |                       | interpretation.                           |
   +-----------------------+-------------------------------------------+

   Table 11: PA-TNC Error Codes for Software Message and Attributes for
                                  PA-TNC

   The following subsections describe the structures present in the
   Error Information fields.

4.16.1.  SW_ERROR, SW_SUBSCRIPTION_DENIED_ERROR and
         SW_SUBSCRIPTION_ID_REUSE_ERROR Information

   The SW_ERROR error code indicates that the sender (the SW-PC) has
   encountered an error related to the processing of a SW Request
   attribute but which is not covered by more specific SW error codes.
   The SW_SUBSCRIPTION_DENIED_ERROR is used when the SW-PV requests to
   establish a subscription or clear all subscriptions from the given
   SW-PV, but the SW-PC is unable or unwilling to comply with this



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   request.  The SW_SUBSCRIPTION_ID_REUSE_ERROR is used when the SW-PC
   receives a SW Request whose Request ID duplicates a Subscription ID
   of an active subscription with the request's sender.  All of these
   error codes use the following error information structure.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Copy of Request ID / Subscription ID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Description (variable length)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Figure 13: SW Error, Subscription Error, and Subscription ID Reuse
                                Information

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Copy of      | In the case that this error condition is generated |
   | Request ID / | in direct response to a SW Request attribute, this |
   | Subscription | field MUST contain an exact copy of the Request ID |
   | ID           | field in the SW Request attribute that caused this |
   |              | error.  In the case that the attribute in question |
   |              | is generated in fulfillment of an active           |
   |              | subscription, this field MUST contain the          |
   |              | Subscription ID of the subscription for which the  |
   |              | attribute was generated.  (This is only possible   |
   |              | if the error code is SW_ERROR as the other errors  |
   |              | are not generated by subscription fulfillment.)    |
   |              | Note that, in this case, the indicated error       |
   |              | appears as a sub-error for a                       |
   |              | SW_SUBSCRIPTION_FULFILLMENT_ERROR, as described in |
   |              | Section 4.16.3.                                    |
   |              |                                                    |
   | Description  | A UTF-8 string describing the condition that       |
   |              | caused this error. This field MAY be 0-length.     |
   |              | However, senders SHOULD include some description   |
   |              | in all PA-TNC Error attributes of these types.     |
   |              | This field MUST NOT be NULL terminated.            |
   +--------------+----------------------------------------------------+

     Table 12: SW Error, Subscription Error, and Subscription ID Reuse
                            Information Fields





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   This error information structure is used with SW_ERROR,
   SW_SUBSCRIPTION_DENIED_ERROR, and SW_SUBSCRIPTION_ID_REUSE_ERROR
   status codes to identify the SW Request attribute that precipitated
   the error condition and to describe the error.  The Description field
   contains text describing the error.  The SW-PC MAY encode machine-
   interpretable information in this field, but SHOULD also include a
   human-readable description of the error, since the receiving SW-PV
   might not recognize the SW-PC's encoded information.

4.16.2.  SW_RESPONSE_TOO_LARGE_ERROR Information

   The SW_RESPONSE_TOO_LARGE_ERROR error code indicates that a response
   generated by a SW-PC in response to a SW-PV's SW Request attribute
   was too large to send.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Copy of Request ID / Subscription I              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Maximum Allowed Size                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Description (variable length)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


            Figure 14: SW Response Too Large Error Information























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   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Copy of      | In the case that the attribute in question is      |
   | Request ID / | generated in direct response to a SW Request, this |
   | Subscription | field MUST contain an exact copy of the Request ID |
   | ID           | field in the SW Request attribute that caused this |
   |              | error.  In the case that the attribute in question |
   |              | is generated in fulfillment of an active           |
   |              | subscription, this field MUST contain the          |
   |              | Subscription ID of the subscription for which the  |
   |              | attribute was generated. Note that, in the latter  |
   |              | case, the SW_RESPONSE_TOO_LARGE_ERROR appears as a |
   |              | sub-error for a SW_SUBSCRIPTION_FULFILLMENT_ERROR, |
   |              | as described in Section 4.16.3.                    |
   |              |                                                    |
   | Maximum      | This field MUST contain an unsigned integer        |
   | Allowed Size | indicating the largest permissible size, in bytes, |
   |              | of SW Attribute that the SW-PC is currently        |
   |              | willing to send in response to a SW Request        |
   |              | attribute.                                         |
   |              |                                                    |
   | Description  | A UTF-8 string describing the condition that       |
   |              | caused this error. This field MAY be 0-length.     |
   |              | However, senders SHOULD include some description   |
   |              | in all PA-TNC Error attributes of these types.     |
   |              | This field MUST NOT be NULL terminated.            |
   +--------------+----------------------------------------------------+

         Table 13: SW Response Too Large Error Information Fields

   This error structure is used with the SW_RESPONSE_TOO_LARGE_ERROR
   status code to identify the SW Request attribute that precipitated
   the error condition and to describe the error.  The Maximum Allowed
   Size field indicates the largest attribute the SW-PC is willing to
   send in response to a SW Request under the current circumstances.
   Note that under other circumstances, the SW-PC might be willing to
   return larger or smaller responses than indicated (such as if the
   endpoint connects to the NEA Server using a different network
   protocol).  The other fields in this error information structure have
   the same meanings as corresponding fields in the SW_ERROR and
   SW_SUBSCRIPTION_DENIED_ERROR information structure.

4.16.3.  SW_SUBSCRIPTION_FULFILLMENT_ERROR Information

   The SW_SUBSCRIPTION_FULFILLMENT_ERROR error code indicates that the
   SW-PC encountered an error while fulfilling a subscription.  The
   bytes after the first 4 octets duplicate a PA-TNC Error attribute (as



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   described in Section 4.2.8 of PA-TNC) that is used to identify the
   nature of the encountered error.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Subscription ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |           Sub Error Code Vendor ID            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Sub Error Code                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Sub Error Information (Variable Length)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


         Figure 15: SW Subscription Fulfillment Error Information

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Subscription | This field MUST contain the Subscription ID of the |
   | ID           | subscription whose fulfillment caused this error.  |
   |              |                                                    |
   | Reserved     | This field MUST contain the value of the Reserved  |
   |              | field of a PA-TNC Error attribute that describes   |
   |              | the error condition encountered during             |
   |              | subscription processing.                           |
   |              |                                                    |
   | Sub Error    | This field MUST contain the value of the Error     |
   | Code Vendor  | Code Vendor ID field of a PA-TNC Error attribute   |
   | ID           | that describes the error condition encountered     |
   |              | during subscription processing.                    |
   |              |                                                    |
   | Sub Error    | This field MUST contain the value of the Error     |
   | Code         | Code field of a PA-TNC Error attribute that        |
   |              | describes the error condition encountered during   |
   |              | subscription processing.                           |
   |              |                                                    |
   | Sub Error    | This field MUST contain the value of the Error     |
   | Information  | Information field of a PA-TNC Error attribute that |
   |              | describes the error condition encountered during   |
   |              | subscription processing.                           |
   +--------------+----------------------------------------------------+

      Table 14: SW Subscription Fulfillment Error Information Fields




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   This error structure is used with the
   SW_SUBSCRIPTION_FULFILLMENT_ERROR status code.  The first 4 octets of
   this error structure contain the Subscription ID of the subscription
   that was being fulfilled when the error occurred.  The remaining
   fields of this error structure duplicate the fields of a PA-TNC Error
   attribute, referred to as the "sub-error".  The error code of the
   sub-error corresponds to the type of error that the SW-PC encountered
   while fulfilling the given subscription.  The sub-error MUST NOT have
   an error code of SW_SUBSCRIPTION_FULFILLMENT_ERROR.

   The SW-PC sending a PA-TNC Error attribute with this error code, and
   the SW-PV receiving it, MUST treat the subscription identified by the
   Subscription ID field as cancelled.  All other subscriptions are
   unaffected.

5.  Supported Data Models

   Software Message and Attributes for PA-TNC supports an extensible
   list of data models for representing and transmitting software
   inventory information.  This list of data models appears in the
   Software Data Model IANA table (see Section 9.4).  This document
   provides guidance for an initial set of data models.  Other documents
   might provide guidance on the use of new data models by Software
   Message and Attributes for PA-TNC, and will be referenced by
   extensions to the Software Data Model IANA table.

5.1.  ISO 2015 SWID Tags using XML

   The International Organization for Standardization and the
   International Electrotechnical Commission (ISO/IEC) published the
   specification governing SWID tag construction and use in 2009 with a
   revised version published in 2015.  [SWID] Since that time, a growing
   number of vendors have integrated SWID tags into their software
   products.  Doing so significantly simplifies the task of identifying
   these pieces of software: instead of relying on discovery processes
   that look for clues as to software presence, such as the presence of
   particular files or registry keys, a readily available list of SWID
   tags provides simple and immediate evidence as to the presence of the
   given piece of software.

   SWID Message and Attributes for PA-TNC has no reliance on the
   presence or management of SWID tags on an endpoint as described in
   the ISO specification.  However, the data model for describing
   software that is presented in the ISO specification provides a robust
   and comprehensive way of describing software and is adopted here as a
   means of representing and transmitting software information.  It
   should be emphasized, the use of the ISO SWID tag data model makes no
   assumption as to whether the source of the recorded information was,



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   in fact, an ISO SWID tag harvested from the endpoint or whether the
   information was created using some other source and normalized to the
   SWID format.

5.1.1.  Guidance on Normalizing Source Data to ISO 2015 SWID Tags using
        XML

   TBD

   Don't violate the specification

   Use your own Tag Creator RegID or the Unknown Tag Creator RegID.  Do
   not use some other party's RegID, especially not the RegID of the
   software author if you are not the author.

5.1.2.  Guidance on Creation of Software Identifiers from ISO 2015 SWID
        Tags

   TBD

   Use combination of Tag Creator RegID and Unique ID fields.
   Specifically, format should be NUMBER::TAG_CREATOR_REGID UNIQUE_ID,
   where NUMBER is the length of TAG_CREATOR_REGID in bytes.  The rest
   of the Software Identifier MUST be the concatination of the Tag
   Creator RegID and the Unique ID from the tag, without any connecting
   character or whitespace.

5.2.  ISO 2009 SWID Tags using XML

   As noted above, ISO's SWID tag specification provides a useful data
   model for representation of software information.  As of the writing
   of this specification, while the 2015 specification is considered
   more comprehensive and addresses some issues with the 2009
   specification, 2009-format SWID tags remain far more common in
   deployments.  For this reason, ISO 2009 SWID tags are included in the
   Software Data Model IANA table.

5.2.1.  Guidance on Normalizing Source Data to ISO 2015 SWID Tags using
        XML

   TBD

   Don't violate the specification

   Use your own Tag Creator RegID or the Unknown Tag Creator RegID.  Do
   not use some other party's RegID, especially not the RegID of the
   software author if you are not the author.




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5.2.2.  Guidance on Creation of Software Identifiers from ISO 2015 SWID
        Tags

   TBD

   Use combination of Tag Creator RegID and Unique ID fields.
   Specifically, format should be NUMBER::TAG_CREATOR_REGID UNIQUE_ID,
   where NUMBER is the length of TAG_CREATOR_REGID in bytes.  The rest
   of the Software Identifier MUST be the concatination of the Tag
   Creator RegID and the Unique ID from the tag, without any connecting
   character or whitespace.

6.  Security Considerations

   This section discusses some of the security threats facing Posture
   Collectors and Posture Validators that implement the Software Message
   and Attributes for PA-TNC protocol.  This section primarily notes
   potential issues for implementers to consider, although it does
   contain a handful of normative requirements to address certain
   security issues.  Implementers need to make the final decision as to
   how their implementations address the given issues.  The issues
   identified below focus on capabilities specific to this document.
   Implementers are advised to consult other relevant NEA specifications
   for security issues that are applicable to such components in
   general.

   Reading the Security Considerations section of any well-written
   specification can be discouraging, as a long list of possible threats
   is catalogued.  Keep in mind that no security measure is absolute,
   but each one can be beneficial.  By understanding the weaknesses of
   each security measure, we can put in place countermeasures to protect
   against exploitation of these weaknesses.

6.1.  Evidentiary Value of Software Inventory Evidence Records

   It must be remembered that the accuracy of an endpoints Software
   Inventory Evidence Collection as an indicator of the endpoints
   software load and changes thereon is only as accurate as the tools
   that populate and manage the software inventory evidence records in
   this collection.  Some tools might not be designed to update records
   in the Software Inventory Evidence Collection in real time resulting
   in a collection that is out-of-step with actual system state.
   Moreover, tools might inaccurately characterize software, or fail to
   properly record its removal.  Finally, it is likely that there will
   be software on the endpoint that is not tracked by any source and
   thus is not reflected in the Software Inventory Evidence Collection.
   Users of collected software inventory evidence records need to
   understand that the information provided by the Software Message and



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   Attributes for PA-TNC capability cannot be treated as completely
   accurate.  Nonetheless, having endpoints report this information can
   still provide useful insights into the state of the endpoint's
   software load, and can alert administrators and policy tools of
   situations that require remediation.

6.2.  Sensitivity of Collected Records

   Software records on an endpoint are generally not considered to be
   sensitive, although there can be exceptions to this generalization as
   noted in the section on Privacy Considerations.  In general, an
   endpoint's Software Inventory Evidence Collection can be browsed and
   individual records read by any party with access to the endpoint.
   This is generally not considered to be problematic, as those with
   access to the endpoint can usually learn of everything disclosed by
   that endpoint's records simply by inspecting other parts of the
   endpoint.

   The situation changes when an endpoint's inventory records are
   collected and stored off of the endpoint itself, such as on a NEA
   Server or CMDB.  Inventory records represent a wealth of information
   about the endpoint in question and, for an adversary who does not
   already have access to the endpoint, a collection of the endpoint's
   inventory records might provide many details that are useful for
   mounting an attack.  A list of the inventory records associated with
   an endpoint reveals a list of software installed on the endpoint.
   This list can be very detailed, noting specific versions and even
   patch levels, which an adversary can use to identify vulnerable
   software and design efficacious attacks.

   In addition, other information might also be gleaned from a
   collection of software inventory records:

   o  An inventory record might include information about where the
      product was installed on a given endpoint.  This can reveal
      details about the file organization of that endpoint that an
      attacker can utilize.

   o  An inventory record might include information about how the
      software was provided to the endpoint, who in an organization
      signs off on the package release, and who packaged the product for
      installation.  This information might be used as a starting point
      for the development of supply chain attacks.

   o  Events affecting inventory records are reported with timestamps
      indicating when each given event occurred.  This can give the
      attacker an indication of how quickly an organization distributes




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      patches and updates, helping the attacker determine how long an
      attack window might remain open.

   Any consolidated software inventory is a potential risk, because such
   an inventory can provide an adversary an insight into the
   enterprise's configuration and management process.  It is recommended
   that a centralized software inventory record collection be protected
   against unauthorized access.  Mechanisms to accomplish this can
   include encrypting the data at rest, ensuring that access to the data
   is limited only to necessary individuals and processes, and other
   basic security precautions.

6.3.  Integrity of Endpoint Records

   SW-PCs maintain records of detected changes to the endpoint's
   Software Inventory Evidence Collection.  These records are used to
   respond to a SW-PV's request for change events.  The SW-PV might use
   a list of reported events to update its understanding of the
   endpoint's Software Inventory Evidence Collection without needing to
   receive a full inventory report from the SW-PC.  For this reason,
   preserving the integrity of the SW-PC's record of events is extremely
   important.  If an attacker modifies the SW-PC's record of changes to
   the endpoint's Software Inventory Evidence Collection, this might
   cause the SW-PV's understanding of the endpoint's Software Inventory
   Evidence Collection to differ from its actual state.  Results might
   include leading the SW-PV to believe that absent software was
   present, that present software was absent, that patches have been
   installed even if this is not the case, or to be unaware of other
   changes to Software Inventory Evidence Records.  As such, the SW-PC
   MUST take steps to protect the integrity of its event records.

   In addition, records of established SW-PV subscriptions also require
   protection against manipulation or corruption.  If an attacker is
   able to modify or delete records of an established subscription by a
   SW-PV, the SW-PC might fail to correctly fulfill this subscription.
   The SW-PV would not be aware that its subscription was not being
   correctly fulfilled unless it received additional information that
   indicated a discrepancy.  For example, the SW-PV might collect a full
   inventory and realize from this that certain events had not been
   correctly reported in accordance with an established subscription.
   For this reason, the SW-PC MUST protect the integrity of subscription
   records.

6.4.  SW-PC Access Permissions

   A SW-PC requires sufficient permissions to collect Software Inventory
   Evidence Records from all of its supported sources, as well as
   sufficient permissions to interact with the endpoint's Posture Broker



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   Client.  With regard to the former, this might require permissions to
   read the contents of directories throughout the file system.
   Depending on the operating environment and other activities
   undertaken by a SW-PC (or software that incorporates a SW-PC as one
   of its capabilities) additional permissions might be required by the
   SW-PC software.  The SW-PC SHOULD NOT be granted permissions beyond
   what it needs in order to fulfill its duties.

6.5.  Sanitization of Record Fields

   Not all sources of software inventory evidence are necessarily
   tightly controlled.  For example, consider a source that gathers
   .swid files from the endpoint's file system.  Any party could create
   a new .swid file that could be collected and turned into a Software
   Inventory Evidence Record.  As a result, it is important that the
   contents of source information not be automatically trusted.  In
   particular, tools that read source information and the Software
   Inventory Evidence Records derived therefrom, including SW-PCs, need
   to be careful to sanitize input to prevent buffer overflow attacks,
   encoding attacks, and other weaknesses that might be exploited by an
   adversary who can control the contents of a record.

6.6.  PA-TNC Security Threats

   In addition to the aforementioned considerations the Software Message
   and Attributes for PA-TNC protocol is subject to the same security
   threats as other PA-TNC transactions, as noted in Section 5.2 of PA-
   TNC [RFC5792].  These include, but are not limited to, attribute
   theft, message fabrication, attribute modification, attribute replay,
   attribute insertion, and denial of service.  Implementers are advised
   to consult the PA-TNC specification to better understand these
   security issues.

7.  Privacy Considerations

   As noted in Section 6.2, if an adversary can gain an understanding of
   the software installed on an endpoint, they can utilize this to
   launch attacks and maintain footholds on this endpoint.  For this
   reason, the NEA Server needs to ensure adequate safeguards are in
   place to prevent exposure of collected inventory records.  For
   similar reasons, it is advisable that an endpoint only send records
   to a NEA Server that is authorized to receive this information and
   that can be trusted to safeguard this information after collection.








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8.  Relationship to Other Specifications

   This specification makes frequent reference to and use of other
   specifications.  This section describes these relationships.

   This specification is expected to participate in a standard NEA
   architecture.  As such, it is expected to be used in conjunction with
   the other protocols used in a NEA exchange.  In particular, SW
   Attributes are conveyed over PB-TNC [RFC5793], which is in turn
   conveyed over some variant of PT (either PT-TLS [RFC6876] or PT-EAP
   [RFC7171]).  These protocols have an especially important role, as
   they are responsible for ensuring that attributes defined under this
   specification are delivered reliably, securely, and to the
   appropriate party.

   It is important to note that the Product Information, Numeric
   Version, and String Version attributes defined in the PA-TNC
   specification [RFC5792] are also meant to convey information about
   installed applications and the versions thereof.  As such, there is
   some conceptual overlap between those attributes and the intent of
   this specification.  However, PA-TNC was designed to respond to very
   specific queries about specific classes of products, while the
   Software Message and Attributes for PA-TNC specification is able to
   convey a broader query, resulting in a more comprehensive set of
   evidence regarding an endpoint's installed software.  As such, this
   specification provides important capabilities not present in the PA-
   TNC specification.

9.  IANA Considerations

   This section extends multiple existing IANA registries.
   Specifically, it extends the PA-TNC Attribute Types and PA-TNC Error
   Codes defined in the PA-TNC specification [RFC5792] and the PA-
   Subtypes registry defined in the PB-TNC specification [RFC5793] and
   extended in PA-TNC.  This specification only adds values to these
   registries and does not alter how these registries work or are
   maintained.  Consult the appropriate specifications for details on
   the operations and maintenance of these registries.

9.1.  Registry for PA-TNC Attribute Types

   Section 4.6 of this specification defines several new PA-TNC
   attributes.  The following values are added to the registry for PA-
   TNC Attribute Types defined in the PA-TNC specification.  Note that
   Table 4 in Section 4.6 lists these attributes but uses a hexadecimal
   value to identify their associated integer.  The integer values given
   in that table are identical to those provided here.  Note also that
   Table 4 includes an entry for PA-TNC Error attributes, but the IANA



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   information associated with that attribute is already defined in the
   PA-TNC specification and is not reproduced here.

   +-----+---------+---------------------+-----------------------------+
   | PEN | Integer | Name                | Defining Specification      |
   +-----+---------+---------------------+-----------------------------+
   | 0   | 17      | SW Request          | Software Message and        |
   |     |         |                     | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 18      | Software Identifier | Software Message and        |
   |     |         | Inventory           | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 19      | Software Identifier | Software Message and        |
   |     |         | Events              | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 20      | Software Inventory  | Software Message and        |
   |     |         |                     | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 21      | Software Events     | Software Message and        |
   |     |         |                     | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 22      | Subscription Status | Software Message and        |
   |     |         | Request             | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 23      | Subscription Status | Software Message and        |
   |     |         | Response            | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 24      | Subscription Status | Software Message and        |
   |     |         | Response            | Attributes for PA-TNC       |
   |     |         |                     |                             |
   | 0   | 25 - 31 | Reserved for future | Software Message and        |
   |     |         | use                 | Attributes for PA-TNC       |
   +-----+---------+---------------------+-----------------------------+

9.2.  Registry for PA-TNC Error Codes

   Section 4.16 of this specification defines several new PA-TNC Error
   Codes.  The following values are added to the registry for PA-TNC
   Error Codes defined in the PA-TNC specification.  Note that Table 11
   in Section 4.16 lists these codes but uses a hexadecimal value to
   identify their associated integer.  The integer values given in that
   table are identical to those provided here.









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   +-----+---------+-----------------------------------+---------------+
   | PEN | Integer | Name                              | Defining      |
   |     |         |                                   | Specification |
   +-----+---------+-----------------------------------+---------------+
   | 0   | 32      | SW_ERROR                          | Software      |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 33      | SW_SUBSCRIPTION_DENIED_ERROR      | Software      |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 34      | SW_RESPONSE_TOO_LARGE_ERROR       | Software      |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 35      | SW_SUBSCRIPTION_FULFILLMENT_ERROR | Software      |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 36      | SW_SUBSCRIPTION_ID_REUSE_ERROR    | Software      |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 37-47   | Reserved for future use           | Software      |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   +-----+---------+-----------------------------------+---------------+

9.3.  Registry for PA Subtypes

   Section 4.1 of this specification defines one new PA Subtype.  The
   following value is added to the registry for PA Subtypes defined in
   the PB-TNC specification.

   +-----+---------+-------------+-------------------------------------+
   | PEN | Integer | Name        | Defining Specification              |
   +-----+---------+-------------+-------------------------------------+
   | 0   | 9       | SW          | Software Message and Attributes for |
   |     |         | Attributes  | PA-TNC                              |
   +-----+---------+-------------+-------------------------------------+




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9.4.  Registry for Software Data Models

   TBD

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <http://www.rfc-editor.org/info/rfc3339>.

   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
              <http://www.rfc-editor.org/info/rfc5198>.

   [RFC5209]  Sangster, P., Khosravi, H., Mani, M., Narayan, K., and J.
              Tardo, "Network Endpoint Assessment (NEA): Overview and
              Requirements", RFC 5209, DOI 10.17487/RFC5209, June 2008,
              <http://www.rfc-editor.org/info/rfc5209>.

   [RFC5792]  Sangster, P. and K. Narayan, "PA-TNC: A Posture Attribute
              (PA) Protocol Compatible with Trusted Network Connect
              (TNC)", RFC 5792, DOI 10.17487/RFC5792, March 2010,
              <http://www.rfc-editor.org/info/rfc5792>.

   [SWID]     The International Organization for Standardization/
              International Electrotechnical Commission, "Information
              Technology - Software Asset Management - Part 2: Software
              Identification Tag, ISO/IEC 19770-2", November 2009.

10.2.  Informative References

   [NIST-SWID]
              The National Institute of Standards and Technology and The
              MITRE Corporation, "Guidelines for the Creation of
              Interoperable Software Identification (SWID) Tags", August
              2013.

   [RFC5793]  Sahita, R., Hanna, S., Hurst, R., and K. Narayan, "PB-TNC:
              A Posture Broker (PB) Protocol Compatible with Trusted
              Network Connect (TNC)", RFC 5793, DOI 10.17487/RFC5793,
              March 2010, <http://www.rfc-editor.org/info/rfc5793>.



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   [RFC6876]  Sangster, P., Cam-Winget, N., and J. Salowey, "A Posture
              Transport Protocol over TLS (PT-TLS)", RFC 6876,
              DOI 10.17487/RFC6876, February 2013,
              <http://www.rfc-editor.org/info/rfc6876>.

   [RFC7171]  Cam-Winget, N. and P. Sangster, "PT-EAP: Posture Transport
              (PT) Protocol for Extensible Authentication Protocol (EAP)
              Tunnel Methods", RFC 7171, DOI 10.17487/RFC7171, May 2014,
              <http://www.rfc-editor.org/info/rfc7171>.

Authors' Addresses

   Chris Coffin
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: ccoffin@mitre.org


   Daniel Haynes
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: dhaynes@mitre.org


   Charles Schmidt
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: cmschmidt@mitre.org


   Jessica Fitzgerald-McKay
   Department of Defense
   9800 Savage Road
   Ft. Meade, Maryland
   USA

   Email: jmfitz2@nsa.gov





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