--- 1/draft-ietf-dtn-bpsec-01.txt 2016-07-07 00:15:57.542414600 -0700 +++ 2/draft-ietf-dtn-bpsec-02.txt 2016-07-07 00:15:57.610416295 -0700 @@ -1,242 +1,296 @@ Delay-Tolerant Networking E. Birrane -Internet-Draft JHU/APL -Intended status: Experimental J. Mayer -Expires: September 20, 2016 INSYEN AG - D. Iannicca - NASA GRC - March 19, 2016 +Internet-Draft K. McKeever +Intended status: Experimental JHU/APL +Expires: January 7, 2017 July 6, 2016 Bundle Protocol Security Specification - draft-ietf-dtn-bpsec-01 + draft-ietf-dtn-bpsec-02 Abstract - This document defines a security protocol providing data integrity - and confidentiality services for the Bundle Protocol. Capabilities - are provided to protect blocks in a bundle along a single path - through a network. + This document defines a security protocol providing end to end data + integrity and confidentiality services for the Bundle Protocol. 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 September 20, 2016. + This Internet-Draft will expire on January 7, 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 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 - 1.1. Related Documents . . . . . . . . . . . . . . . . . . . . 3 - 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 - 2. Key Properties . . . . . . . . . . . . . . . . . . . . . . . 6 - 2.1. Block-Level Granularity . . . . . . . . . . . . . . . . . 6 - 2.2. Multiple Security Sources . . . . . . . . . . . . . . . . 6 - 2.3. Mixed Security Policy . . . . . . . . . . . . . . . . . . 7 + 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3 + 1.2. Supported Security Services . . . . . . . . . . . . . . . 3 + 1.3. Specification Scope . . . . . . . . . . . . . . . . . . . 4 + 1.4. Related Documents . . . . . . . . . . . . . . . . . . . . 5 + 1.5. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 + 2. Key Properties . . . . . . . . . . . . . . . . . . . . . . . 7 + 2.1. Block-Level Granularity . . . . . . . . . . . . . . . . . 7 + 2.2. Multiple Security Sources . . . . . . . . . . . . . . . . 7 + 2.3. Mixed Security Policy . . . . . . . . . . . . . . . . . . 8 2.4. User-Selected Ciphersuites . . . . . . . . . . . . . . . 8 - 2.5. Deterministic Processing . . . . . . . . . . . . . . . . 8 - 3. Security Block Definitions . . . . . . . . . . . . . . . . . 8 - 3.1. Block Identification . . . . . . . . . . . . . . . . . . 9 - 3.2. Block Representation . . . . . . . . . . . . . . . . . . 9 - 3.2.1. CMS Block Type-Specific Data Fields . . . . . . . . . 10 - 3.2.2. BIB and BCB Block Type-Specific Data Fields . . . . . 10 - 3.3. Block Ordering . . . . . . . . . . . . . . . . . . . . . 11 - 3.4. Block Integrity Block . . . . . . . . . . . . . . . . . . 12 - 3.5. Block Confidentiality Block . . . . . . . . . . . . . . . 13 - 3.6. Cryptographic Message Syntax Block . . . . . . . . . . . 15 - 3.7. Block Interactions . . . . . . . . . . . . . . . . . . . 16 - 3.8. Parameters and Result Fields . . . . . . . . . . . . . . 17 - 3.9. BSP Block Example . . . . . . . . . . . . . . . . . . . . 19 - 4. Security Processing . . . . . . . . . . . . . . . . . . . . . 22 - 4.1. Canonical Forms . . . . . . . . . . . . . . . . . . . . . 22 - 4.1.1. Block Canonicalization . . . . . . . . . . . . . . . 22 - 4.1.2. Considerations . . . . . . . . . . . . . . . . . . . 25 - 4.2. Endpoint ID Confidentiality . . . . . . . . . . . . . . . 25 - 4.3. Bundles Received from Other Nodes . . . . . . . . . . . . 26 - 4.3.1. Receiving BCB Blocks . . . . . . . . . . . . . . . . 26 - 4.3.2. Receiving BIB Blocks . . . . . . . . . . . . . . . . 26 - 4.4. Receiving CMSB Blocks . . . . . . . . . . . . . . . . . . 27 - 4.5. Bundle Fragmentation and Reassembly . . . . . . . . . . . 27 - 4.6. Reactive Fragmentation . . . . . . . . . . . . . . . . . 28 - 5. Key Management . . . . . . . . . . . . . . . . . . . . . . . 28 - 6. Policy Considerations . . . . . . . . . . . . . . . . . . . . 28 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 29 - 8. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 29 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 - 9.1. Bundle Block Types . . . . . . . . . . . . . . . . . . . 30 - 9.2. Cipher Suite Flags . . . . . . . . . . . . . . . . . . . 30 - 9.3. Parameters and Results . . . . . . . . . . . . . . . . . 31 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 31 - 10.2. Informative References . . . . . . . . . . . . . . . . . 32 - - Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 32 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 + 2.5. Deterministic Processing . . . . . . . . . . . . . . . . 9 + 3. Security Block Definitions . . . . . . . . . . . . . . . . . 9 + 3.1. Block Identification . . . . . . . . . . . . . . . . . . 10 + 3.2. Block Representation . . . . . . . . . . . . . . . . . . 10 + 3.3. Block Integrity Block . . . . . . . . . . . . . . . . . . 13 + 3.4. Block Confidentiality Block . . . . . . . . . . . . . . . 14 + 3.5. Block Interactions . . . . . . . . . . . . . . . . . . . 16 + 3.6. Multi-Target Block Definitions . . . . . . . . . . . . . 17 + 3.7. Parameters and Result Fields . . . . . . . . . . . . . . 17 + 3.8. BSP Block Example . . . . . . . . . . . . . . . . . . . . 18 + 4. Canonical Forms . . . . . . . . . . . . . . . . . . . . . . . 20 + 4.1. Technical Notes . . . . . . . . . . . . . . . . . . . . . 20 + 4.2. Primary Block Canonicalization . . . . . . . . . . . . . 21 + 4.3. Non-Primary-Block Canonicalization . . . . . . . . . . . 22 + 5. Security Processing . . . . . . . . . . . . . . . . . . . . . 22 + 5.1. Bundles Received from Other Nodes . . . . . . . . . . . . 23 + 5.1.1. Receiving BCB Blocks . . . . . . . . . . . . . . . . 23 + 5.1.2. Receiving BIB Blocks . . . . . . . . . . . . . . . . 23 + 5.2. Bundle Fragmentation and Reassembly . . . . . . . . . . . 24 + 6. Key Management . . . . . . . . . . . . . . . . . . . . . . . 25 + 7. Policy Considerations . . . . . . . . . . . . . . . . . . . . 25 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 26 + 8.1. Attacker Capabilities and Objectives . . . . . . . . . . 27 + 8.2. Attacker Behaviors and BPSec Mitigations . . . . . . . . 28 + 8.2.1. Eavesdropping Attacks . . . . . . . . . . . . . . . . 28 + 8.2.2. Modification Attacks . . . . . . . . . . . . . . . . 28 + 8.2.3. Topology Attacks . . . . . . . . . . . . . . . . . . 29 + 8.2.4. Message Injection . . . . . . . . . . . . . . . . . . 30 + 9. Ciphersuite Authorship Considerations . . . . . . . . . . . . 30 + 10. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 31 + 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 + 11.1. Bundle Block Types . . . . . . . . . . . . . . . . . . . 31 + 11.2. Cipher Suite Flags . . . . . . . . . . . . . . . . . . . 31 + 11.3. Parameters and Results . . . . . . . . . . . . . . . . . 32 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 + 12.1. Normative References . . . . . . . . . . . . . . . . . . 33 + 12.2. Informative References . . . . . . . . . . . . . . . . . 33 + Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 34 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 1. Introduction This document defines security features for the Bundle Protocol [BPBIS] intended for use in delay-tolerant networks, in order to provide Delay-Tolerant Networking (DTN) security services. +1.1. Motivation + The Bundle Protocol is used in DTNs that overlay multiple networks, some of which may be challenged by limitations such as intermittent and possibly unpredictable loss of connectivity, long or variable delay, asymmetric data rates, and high error rates. The purpose of the Bundle Protocol is to support interoperability across such stressed networks. The stressed environment of the underlying networks over which the Bundle Protocol operates makes it important for the DTN to be protected from unauthorized use, and this stressed environment poses unique challenges for the mechanisms needed to secure the Bundle Protocol. Furthermore, DTNs may be deployed in environments where a portion of the network might become compromised, posing the usual - security challenges related to confidentiality, integrity, and - availability. + security challenges related to confidentiality and integrity. + +1.2. Supported Security Services + + This specification supports end-to-end integrity and confidentiality + services associated with BP bundles. + + Integrity services ensure data within a bundle are not changed. Data + changes may be caused by processing errors, environmental conditions, + or intentional manipulation. An integrity service is one that + provides sufficient confidence to a data receiver that data has not + changed since its value was last asserted. + + Confidentiality services ensure that the values of some data within a + bundle can only be determined by authorized receivers of the data. + When a bundle traverses a DTN, many nodes in the network other than + the destination node MAY see the contents of a bundle. A + confidentiality service allows a destination node to generate data + values from otherwise encrypted contents of a bundle. + + NOTE: Hop-by-hop authentication is NOT a supported security service + in this specification, for three reasons. + + 1. The term "hop-by-hop" is ambiguous in a BP overlay, as nodes that + are adjacent in the overlay may not be adjacent in physical + connectivity. This condition is difficult or impossible to + predict in the overlay and therefore makes the concept of hop-by- + hop authentication difficult or impossible to enforce at the + overlay. + + 2. Networks in which BPSec may be deployed may have a mixture of + security-aware and not-security-aware nodes. Hop-by-hop + authentication cannot be deployed in a network if adjacent nodes + in the network have different security capabilities. + + 3. Hop-by-hop authentication can be viewed as a special case of data + integrity. As such, it is possible to develop policy that + provides a version of authentication using the integrity + mechanisms defined in this specification. + +1.3. Specification Scope This document describes the Bundle Protocol Security Specification - (BPSec), which provides security services for blocks within a bundle - from the bundle source to the bundle destination. Specifically, - BPSec provides integrity and confidentiality for bundles along a path - through a DTN. + (BPSec), which provides security services for blocks within a bundle. + This includes the data specification for individual BP extension + blocks and the processing instructions for those blocks. BPSec applies, by definition, only to those nodes that implement it, known as "security-aware" nodes. There MAY be other nodes in the DTN that do not implement BPSec. All nodes can interoperate with the exception that BPSec security operations can only happen at BPSec security-aware nodes. -1.1. Related Documents + This specification does not address individual cipher suite + implementations. The definition and enumeration of cipher suites + should be undertaken in separate specification documents. + + This specification does not address the implementation of security + policy and does not provide a security policy for the BPSec. + Security policies are typically based on the nature and capabilities + of individual networks and network operational concepts. However, + this specification does recommend policy considerations when building + a security policy. + + This specification does not address how to combine the BPSec security + blocks with other protocols, other BP extension blocks, or other best + practices to achieve security in any particular network + implementation. + +1.4. Related Documents This document is best read and understood within the context of the following other DTN documents: "Delay-Tolerant Networking Architecture" [RFC4838] defines the architecture for delay-tolerant networks, but does not discuss security at any length. The DTN Bundle Protocol [BPBIS] defines the format and processing of the blocks used to implement the Bundle Protocol, excluding the security-specific blocks defined here. The Bundle Security Protocol [RFC6257] and Streamlind Bundle Security Protocol [SBSP] introduce the concepts of security blocks for security services. BPSec is based off of these documents. -1.2. Terminology +1.5. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. - We introduce the following terminology for purposes of clarity. + This section defines those terms whose definition is important to the + understanding of concepts within this specification. o Source - the bundle node from which a bundle originates. o Destination - the bundle node to which a bundle is ultimately destined. o Forwarder - the bundle node that forwarded the bundle on its most recent hop. o Intermediate Receiver, Waypoint, or "Next Hop" - the neighboring bundle node to which a forwarder forwards a bundle. o Path - the ordered sequence of nodes through which a bundle passes on its way from source to destination. The path is not necessarily known by the bundle, or any bundle-aware nodes. - Figure 1 below is adapted from [BPBIS] and shows four bundle nodes - (denoted BN1, BN2, BN3, and BN4) that reside above some transport - layer(s). Three distinct transport and network protocols (denoted - T1/N1, T2/N2, and T3/N3) are also shown. + The application of these terms applied to a sample network topology + is shown in Figure 1. This figure shows four bundle nodes (BN1, BN2, + BN3, BN4) residing above some transport layer(s). Three distinct + transport and network protocols (T1/N1, T2/N2, and T3/N3) are also + shown. +---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+ | BN1 v | | ^ BN2 v | | ^ BN3 v | | ^ BN4 | +---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+ | T1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ T3 | +---------v-+ +-^---------v-+ +-^---------v + +-^---------+ | N1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ N3 | +---------v-+ +-^---------v + +-^---------v-+ +-^---------+ | >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ | +-----------+ +------------+ +-------------+ +-----------+ | | | | |<-- An Internet --->| |<--- An Internet --->| | | | | - Figure 1: Bundle Nodes Sitting at the Application Layer of the - Internet Model + Figure 1: Bundle Nodes Sitting Above the Transport Layer. - BN1 originates a bundle that it forwards to BN2. BN2 forwards the - bundle to BN3, and BN3 forwards the bundle to BN4. BN1 is the source - of the bundle and BN4 is the destination of the bundle. BN1 is the - first forwarder, and BN2 is the first intermediate receiver; BN2 then - becomes the forwarder, and BN3 the intermediate receiver; BN3 then - becomes the last forwarder, and BN4 the last intermediate receiver, - as well as the destination. + Consider the case where BN1 originates a bundle that it forwards to + BN2. BN2 forwards the bundle to BN3, and BN3 forwards the bundle to + BN4. BN1 is the source of the bundle and BN4 is the destination of + the bundle. BN1 is the first forwarder, and BN2 is the first + intermediate receiver; BN2 then becomes the forwarder, and BN3 the + intermediate receiver; BN3 then becomes the last forwarder, and BN4 + the last intermediate receiver, as well as the destination. If node BN2 originates a bundle (for example, a bundle status report or a custodial signal), which is then forwarded on to BN3, and then to BN4, then BN2 is the source of the bundle (as well as being the first forwarder of the bundle) and BN4 is the destination of the bundle (as well as being the final intermediate receiver). - We introduce the following security-specific DTN terminology. + The following security-specific terminology is also defined to + clarify security operations in this specifiation. o Security-Service - the security features supported by this - specification: authentication, integrity, and confidentiality. + specification: integrity and confidentiality. o Security-Source - a bundle node that adds a security block to a bundle. - o Security-Target - the portion of a bundle (e.g., the primary - block, payload block, extension block, or entire bundle) that - receives a security-service as part of a security-operation. + o Security-Target - the block within a bundle that receives a + security-service as part of a security-operation. - o Security Block - a single instance of a BPSec extension block in a - bundle. + o Security Block - a BPSec extension block in a bundle. o Security-Operation - the application of a security-service to a - specific security-target, notated as OP(security-service, - security-target). For example, OP(authentication, bundle) or - OP(confidentiality, payload). Every security-operation in a - bundle MUST be unique, meaning that a security-service can only be - applied to a security-target once in a bundle. A security- - operation MAY be implemented by one or more security blocks. + security-target, notated as OP(security-service, security-target). + For example, OP(confidentiality, payload). Every security- + operation in a bundle MUST be unique, meaning that a security- + service can only be applied to a security-target once in a bundle. + A security operation is implemented by a security block. 2. Key Properties The application of security services in a DTN is a complex endeavor that must consider physical properties of the network, policies at each node, and various application security requirements. Rather than enumerate all potential security implementations in all potential DTN topologies, this specification defines a set of key properties of a security system. The security primitives outlined in this document MUST enable the realization of these properties in a @@ -257,400 +311,378 @@ Security services within this specification MUST provide block level granularity where applicable such that different blocks within a bundle may have different security services applied to them. For example, within a bundle, a payload might be encrypted to protect its contents, whereas an extension block containing summary information related to the payload might be integrity signed but otherwise unencrypted to provide certain nodes access to payload- related data without providing access to the payload. + Each security block in a bundle will be associated with a specific + security-operation. + 2.2. Multiple Security Sources + A bundle MAY have multiple security blocks and these blocks MAY have + different security-sources. + The Bundle Protocol allows extension blocks to be added to a bundle at any time during its existence in the DTN. When a waypoint node adds a new extension block to a bundle, that extension block may have security services applied to it by that waypoint. Similarly, a waypoint node may add a security service to an existing extension block, consistent with its security policy. For example, a node representing a boundary between a trusted part of the network and an untrusted part of the network may wish to apply payload encryption for bundles leaving the trusted portion of the network. - In each case, a node other than the bundle originator may be adding a + In each case, a node other than the bundle originator may add a security service to the bundle and, as such, the source for the security service will be different than the source of the bundle itself. Security services MUST track their orginating node so as to properly apply policy and key selection associated with processing the security service at the bundle destination. Referring to Figure 1, if the bundle that originates at BN1 is given security blocks by BN1, then BN1 is the security-source for those blocks as well as being the source of the bundle. If the bundle that originates at BN1 is then given a security block by BN2, then BN2 is the security-source for that block even though BN1 remains the bundle source. - A bundle MAY have multiple security blocks and these blocks MAY have - different security-sources. Each security block in a bundle will be - associated with a specific security-operation. All security blocks - comprising a security-operation MUST have the same security-source. - - As required in [BPBIS], forwarding nodes MUST transmit blocks in a - bundle in the same order in which they were received. This - requirement applies to all DTN nodes, not just ones that implement - security processing. Blocks in a bundle MAY be added or deleted - according to the applicable specification, but those blocks that are - both received and transmitted MUST be transmitted in the same order - that they were received. - 2.3. Mixed Security Policy Different nodes in a DTN may have different security-related capabilities. Some nodes may not be security-aware and will not understand any security-related extension blocks. Other nodes may have security policies that require evaluation of security services at places other than the bundle destination (such as verifying integrity signatures at certain waypoint nodes). Other nodes may ignore any security processing if they are not the destination of the bundle. The security services described in this specification must allow each of these scenarios. Extension blocks representing security services MUST have their block - processing flags set such that the block (and bundle, where - applicable) will be treated appropriately by non-security-aware - nodes. + processing flags set such that the block will be treated + appropriately by non-security-aware nodes. Extension blocks providing integrity services within a bundle MUST support options to allow waypoint nodes to evaluate these signatures if such nodes have the proper configuraton to do so. 2.4. User-Selected Ciphersuites - The security services defined in this specification rely on a a - variety of ciphersuites providing integrity signatures, ciphertext, - and other information necessary to populate security blocks. Users - may wish to select differing ciphersuites to implement different - security services. For example, some users may wish to use a SHA-1 - based hash for integrity whereas other users may require a SHA-2 hash - instead. The security services defined in this specification MUST - provide a mechanism for identifying what ciphersuite has been used to - populate a security block. + The security services defined in this specification rely on a variety + of cipher suites providing integrity signatures, ciphertext, and + other information necessary to populate security blocks. Users may + wish to select different cipher suites to implement different + security services. For example, some users may wish to use a SHA-256 + based hash for integrity whereas other users may require a SHA-384 + hash instead. The security services defined in this specification + MUST provide a mechanism for identifying what cipher suite has been + used to populate a security block. 2.5. Deterministic Processing In all cases, the processing order of security services within a bundle must avoid ambiguity when evaluating security at the bundle destination. This specification MUST provide determinism in the application and evaluation of security services, even when doing so results in a loss of flexibility. 3. Security Block Definitions - There are three types of security blocks that MAY be included in a - bundle. These are the Block Integrity Block (BIB), the Block - Confidentiality Block (BCB), and the Cryptographic Messaging Syntax - Block (CMSB). + There are two types of security blocks that may be included in a + bundle. These are the Block Integrity Block (BIB) and the Block + Confidentiality Block (BCB). - The BIB is used to ensure the integrity of its security-target. + The BIB is used to ensure the integrity of its security-target(s). The integrity information in the BIB MAY (when possible) be verified by any node in between the BIB security-source and the bundle destination. BIBs MAY be added to, and removed from, bundles as a matter of security policy. - The BCB indicates that the security-target has been encrypted, in - whole or in part, at the BCB security-source in order to protect - its content while in transit. The BCB may be decrypted by + The BCB indicates that the security-target(s) has been encrypted, + in whole or in part, at the BCB security-source in order to + protect its content while in transit. The BCB may be decrypted by appropriate nodes in the network, up to and including the bundle destination, as a matter of security policy. - The CMSB contains a Cryptographic Message Syntax (CMS) payload - used to describe a security service applied to another extension - block. NOTE: Applications may choose to simply place CMS text as - the payload to the bundle. In such cases, security is considered - to be implemented at the application layer and CMSBs are not - required in that case. - - Certain cipher suites may allow or require multiple instances of a - block to appear in the bundle. For example, an integrity cipher - suite may require two security blocks, one before the payload block - and one after. Despite the presence of two security blocks, they - both comprise the same security-operation - OP(integirty, target) in - this example. - A security-operation MUST NOT be applied more than once in a bundle. For example, the two security-operations: OP(integrity, payload) and OP(integrity, payload) are considered redundant and MUST NOT appear together in a bundle. However, the two security operations OP(integrity, payload) and OP(integrity, extension_block_1) MAY both be present in the bundle. Also, the two security operations OP(integrity, extension_block_1) and OP(integrity, extension_block_2) are unique and may both appear in the same bundle. - Many of the fields in these block definitions use the Self-Delimiting - Numeric Value (SDNV) type whose format and encoding is as defined in - [BPBIS]. + If the same security-service is to be applied to multiple security- + targets, and cipher suite parameters for each security service are + identical, then the set of security-operations can be represented as + a single security-block with multiple security-targets. In such a + case, all security-operations represented in the security-block MUST + be applied/evaluated together. 3.1. Block Identification This specification requires that every target block of a security operation be uniquely identifiable. The definition of the extension - block header from [BPBIS] provides such a mechanism in the "block - number", which provides a unique identifier for a block within a - bundle. Within this specification, a target block will be identified - by its unique block number. + block header from [BPBIS] provides such a mechanism in the "Block + Number" field, which provides a unique identifier for a block within + a bundle. Within this specification, a security-target will be + identified by its unique Block Number. 3.2. Block Representation Each security block uses the Canonical Bundle Block Format as defined in [BPBIS]. That is, each security block is comprised of the following elements: o Block Type Code o Block Number o Block Processing Control Flags + o CRC Type and CRC Field + o Block Data Length o Block Type Specific Data Fields -3.2.1. CMS Block Type-Specific Data Fields - - The contents of the CMS block is a single field of CMS data whose - length is specified by the BLock Data Length parameter. - -3.2.2. BIB and BCB Block Type-Specific Data Fields - - The structure of the BIB and BCB type-specific data fields are - identifcal and given in Figure 2. Although the diagram hints at a - fixed-format layout, this is purely for the purpose of exposition. - Except for the "type" field, all fields are variable in length. - Fields annotated with an '*' are optional, with their inclusion in - the block indicated by the cipher suite flags field. + The structure of the BIB and BCB Block Type Specific Data fields are + identifcal and illustrated in Figure 2. In this figure, field names + prefaced with an '*' are optional and their inclusion in the block is + indicated by the Cipher Suite Flags field. - +---------------------------+-------------------------+ - | Security Target (SDNV) | Cipher suite ID (SDNV) | - +---------------------------+-------------------------+ - | Cipher suite Flags (SDNV) | *Source EID (Compound) | - +---------------------------+-------------------------+ - | *Parameters (Compound) | *Sec. Result (Compound) | - +---------------------------+-------------------------+ + +================================================= + | Field Name | Field Data Type | + +================================================= + | # Security Targets | Unsigned Integer | + +---------------------+--------------------------+ + | Security Targets | Array (Unsigned Integer) | + +---------------------+--------------------------+ + | Cipher Suite ID | Unsigned Integer | + +---------------------+--------------------------+ + | Cipher Suite Flags | Unsigned Integer | + +---------------------+--------------------------+ + | Security Source | URI - OPTIONAL | + +---------------------+--------------------------+ + | Cipher Parameters | Byte Array - OPTIONAL | + +---------------------+--------------------------+ + | Security Result | Byte Array | + +---------------------+--------------------------+ Figure 2: BIB and BCB Block Structure - The BIB and BCB type-specific data fields consist of the following - fields, some of which are optional. + Where the block fields are identified as follows. - o Security-Target (SDNV) - Uniquely identifies the target of the - associated security-operation. This MUST be the block number of a - block in the bundle. + o # Security Targets - The number of security targets for this + security block. This value MUST be at least 1. - o Cipher suite ID (SDNV) - Identifies the ciphersuite used to - implement the security service reprsented by this block. + o Security-Targets - This array contains the unique identifier of + the blocks targetted by this security operation. Each security- + target MUST represent a block present in the bundle. A security- + target MUST NOT be repeated in this array. - o Cipher suite flags (SDNV) - Identifies which optional security - block fields are present in the block. The structure of the - cipher suite flags field is shown in Figure 3. The presence of an + o Cipher suite ID - Identifies the cipher suite used to implement + the security service represented by this block and applied to each + security-target. + + o Cipher suite flags - Identifies which optional security block + fields are present in the block. The structure of the Cipher + Suite Flags field is shown in Figure 3. The presence of an optional field is indicated by setting the value of the corresponding flag to one. A value of zero indicates the - corresponding optional field is not present. The BPSEC cipher - suite flags are defined as follows. + corresponding optional field is not present. The BPSEC Cipher + Suite Flags are defined as follows. - * bits 6-3 are reserved for future use. + Bit Bit Bit Bit Bit Bit Bit Bit + 7 6 5 4 3 2 1 0 + +-----------------------------------+-----+-----+ + | reserved | src |parm | + +-----------------------------------+-----+-----+ + MSB LSB - * src - bit 2 indicates whether the security source EID is - present in the block. This identifief the EID that inserted - the security service in the bundle. If the security source is - not present then the souce of the block MAY be taken to be the - bundle source, the previous hop, or some other EID as defined - by security policy. + Figure 3: Cipher Suite Flags - * parm - bit 1 indicates whether or not the cipher suite - parameters fields are present in the block. + Where: - * res - bit 0 indicates whether or not the security result fields - are present in the block. + * bits 7-2 are reserved for future use. - Bit Bit Bit Bit Bit Bit Bit - 6 5 4 3 2 1 0 - +-----+-----+-----+-----+-----+-----+-----+ - | reserved | src |parm | res | - +-----+-----+-----+-----+-----+-----+-----+ + * src - bit 1 indicates whether the Security Source EID is + present in the block. - Figure 3: Cipher suite flags + * parm - bit 0 indicates whether or not the Cipher Suite + Parameters field is present in the block. - o (OPTIONAL) Parameters - compound field of the following two items. + o (OPTIONAL) Security Source (URI) - This identifies the EID that + inserted the security service in the bundle. If the security + source is not present then the souce of the block MAY be taken to + be the bundle source, the previous hop, or some other EID as + defined by security policy. - * Length (SDNV) - specifies the length of the next field, which - captures the parameters data. + o (OPTIONAL) Parameters (Byte Array) - Compound field of the + following two items. - * Data - A byte array encoding one or more cipher suite - parameters, with each parameter represented as a Type-Length- - Value (TLV) triplet. In this triplet, the type and length are - represented as SDNVs and the value is a byte array holding the - parmeter. See Section 3.8 for a list of parameter types that - MUST be supported by BPSEC implementations. BPSEC cipher suite + * Length (Unsigned Integer) - specifies the length of the next + field, which captures the parameters data. + + * Data (Byte Array) - A byte array encoding one or more cipher + suite parameters, with each parameter represented as a Type- + Length-Value (TLV) triplet, defined as follows. + + + Type (Byte) - The parameter type. + + + Length (Unsigned Integer) - The length of the parameter. + + + Value (Byte Array) - The parameter value. + + See Section 3.7 for a list of parameter types that MUST be + supported by BPSEC implementations. BPSEC cipher suite specifications MAY define their own parameters to be represented in this byte array. - o (OPTIONAL) Security Result - compound field of the next two items. - - * Length (SDNV) - specifies the length of the next field, which - is the security-result data. + o Security Result (Byte Array) - Compound field of the next two + items. - * Data - A byte array containing the results of the appropriate - cipher suite specific calculation (e.g., a signature, Message - Authentication Code (MAC), or cipher-text block key). + * Length (Unsigned Integer) - specifies the length of the next + field, which is the security-result data. -3.3. Block Ordering + * Data (Byte Array) - A byte array encoding a security result for + each security-target covered by the security-block, with each + entry represented as a TLV and optionally prepended with + information on which security-target is referenced by the + result, as follows. - A security-operation may be implemented in a bundle using either one - or two security blocks. For example, the operation OP(integrity, - block) MAY be accomplished by a single BIB block in the bundle, or it - MAY be accomplished by two BIB blocks in the bundle. To avoid - confusion, we use the following terminology to identify the block or - blocks comprising a security-operation. + + Target (Optional Unsigned Integer) - If the security-block + has multiple security-targets, the target field is the Block + Number of the security-target to which this result field + applies. If the security-block only has a single security- + target, this field is omitted. - The terms "First" and "Last" are used ONLY when describing multiple - security blocks comprising a single security-operation. A "First" - block refers to the security block that is closest to the primary - block in the canonical form of the bundle. A "Last" block refers to - the security block that is furthest from the primary block in the - canonical form of the bundle. + + Type (Unsigned Integer)(Byte) - The type of security result + field. - If a single security block implements the security-operation, then it - is referred to as a "Lone" block. For example, when a bundle - authentication cipher suite requires a single BIB block we refer to - it as a Lone BAB. When a bundle authentication cipher suite requires - two BIB blocks we refer to them as the First BIB and the Last BIB. + + Length (Unsigned Integer) - The length of the result field. - This specification and individual cipher suites impose restrictions - on what optional fields must and must not appear in First blocks, - Last blocks, and Lone blocks. + + Value (Byte Array) - The results of the appropriate cipher + suite specific calculation (e.g., a signature, Message + Authentication Code (MAC), or cipher-text block key). -3.4. Block Integrity Block +3.3. Block Integrity Block - A BIB is an ASB with the following additional restrictions: + A BIB is an ASB with the following characteristics: - The block-type code value MUST be 0x02. + The Block Type Code value MUST be 0x02. - The block processing control flags value can be set to whatever + The Block Processing Control flags value can be set to whatever values are required by local policy. Cipher suite designers should carefully consider the effect of setting flags that either discard the block or delete the bundle in the event that this block cannot be processed. - The security-target MUST match the BLock Number of a block within - the bundle. The security-target for a BIB MUST NOT reference a - security block defined in this specification (BIB, BCB, or CMSB). + A security-target for a BIB MUST NOT reference a security-block + defined in this specification (e.g., a BIB or a BCB). The cipher suite ID MUST be documented as an end-to-end authentication-cipher suite or as an end-to-end error-detection- cipher suite. - The cipher suite parameters field MAY be present in either a Lone - BIB or a First BIB. This field MUST NOT be present in a Last BIB. - - An EID-reference to the security-source MAY be present in either a - Lone BIB or a First BIB. This field MUST NOT be present in a Last - BIB. + An EID-reference to the security-source MAY be present. If this + field is not present, then the security-source of the block SHOULD + be inferred according to security policy and MAY default to the + bundle source. The security-source may also be specified as part + of key-information described in Section 3.7. The security-result captures the result of applying the cipher suite calculation (e.g., the MAC or signature) to the relevant parts of the security-target, as specified in the cipher suite - definition. This field MUST be present in either a Lone BIB or a - Last BIB. This field MUST NOT be present in a First BIB. + definition. This field MUST be present. The cipher suite MAY process less than the entire security-target. If the cipher suite processes less than the complete, original security-target, the cipher suite parameters MUST specify which bytes of the security-target are protected. Notes: o Since OP(integrity, target) is allowed only once in a bundle per target, it is RECOMMENDED that users wishing to support multiple integrity signatures for the same target define a multi-signature - cipher suite, capturing multiple security results in cipher suite - parameters. + cipher suite. o For some cipher suites, (e.g., those using asymmetric keying to produce signatures or those using symmetric keying with a group key), the security information MAY be checked at any hop on the way to the destination that has access to the required keying - information, in accordance with Section 3.7. + information, in accordance with Section 3.5. o The use of a generally available key is RECOMMENDED if custodial transfer is employed and all nodes SHOULD verify the bundle before accepting custody. -3.5. Block Confidentiality Block +3.4. Block Confidentiality Block - A BCB is an ASB with the following additional restrictions: + A BCB is an ASB with the following characteristics: - The block-type code value MUST be 0x03. + The Block Type Code value MUST be 0x03. - The block processing control flags value can be set to whatever - values are required by local policy, except that a Lone BCB or - First BCB MUST have the "replicate in every fragment" flag set. - This indicates to a receiving node that the payload portion in - each fragment represents cipher-text. This flag SHOULD NOT be set - otherwise. Cipher suite designers should carefully consider the - effect of setting flags that either discard the block or delete - the bundle in the event that this block cannot be processed. + The Block Processing Control flags value can be set to whatever + values are required by local policy, except that this block MUST + have the "replicate in every fragment" flag set if the target of + the BCB is the Payload Block. Having that BCB in each fragment + indicates to a receiving node that the payload portion of each + fragment represents cipher-text. Cipher suite designers should + carefully consider the effect of setting flags that either discard + the block or delete the bundle in the event that this block cannot + be processed. - The security-target MUST match the BLock Number of a block within - the bundle. The security-target for a BCB MAY reference the - payload block, a non-security extension block, or a BIB block. + A security-target for a BCB MAY reference the payload block, a + non-security extension block, or a BIB block. A security-target + in a BCB MUST NOT be another BCB. The cipher suite ID MUST be documented as a confidentiality cipher suite. - Key-information, if available, MUST appear only in a Lone BCB or a - First BCB. - Any additional bytes generated as a result of encryption and/or authentication processing of the security-target SHOULD be placed - in an "integrity check value" field (see Section 3.8) in the - security-result of the Lone BCB or Last BCB. - - The cipher suite parameters field MAY be present in either a Lone - BCB or a First BCB. This field MUST NOT be present in a Last BCB. + in an "integrity check value" field (see Section 3.7) or other + such appropriate area in the security-result of the BCB. - An EID-reference to the security-source MAY be present in either a - Lone BCB or a First BCB. This field MUST NOT be present in a Last - BCB. The security-source can also be specified as part of key- - information described in Section 3.8. + An EID-reference to the security-source MAY be present. If this + field is not present, then the security-source of the block SHOULD + be inferred according to security policy and MAY default to the + bundle source. The security-source may also be specified as part + of key-information described in Section 3.7. - The security-result MAY be present in either a Lone BCB or a Last - BCB. This field MUST NOT be present in a First BCB. This - compound field normally contains fields such as an encrypted - bundle encryption key and/or authentication tag. + The security-result MUST be present in the BCB. This compound + field normally contains fields such as an encrypted bundle + encryption key and/or authentication tag. - The BCB is the only security block that modifies the contents of its - security-target. When a BCB is applied, the security-target body - data are encrypted "in-place". Following encryption, the security- - target body data contains cipher-text, not plain-text. Other - security-target block fields (such as type, processing control flags, - and length) remain unmodified. + The BCB modifies the contents of its security-target. When a BCB is + applied, the security-target body data are encrypted "in-place". + Following encryption, the security-target body data contains cipher- + text, not plain-text. Other security-target block fields (such as + type, processing control flags, and length) remain unmodified. Fragmentation, reassembly, and custody transfer are adversely affected by a change in size of the payload due to ambiguity about what byte range of the block is actually in any particular fragment. Therefore, when the security-target of a BCB is the bundle payload, the BCB MUST NOT alter the size of the payload block body data. Cipher suites SHOULD place any block expansion, such as authentication tags (integrity check values) and any padding generated by a block-mode cipher, into an integrity check value item - in the security-result field (see Section 3.8) of the BCB. This "in- + in the security-result field (see Section 3.7) of the BCB. This "in- place" encryption allows fragmentation, reassembly, and custody transfer to operate without knowledge of whether or not encryption has occurred. Notes: o The cipher suite MAY process less than the entire original security-target body data. If the cipher suite processes less than the complete, original security-target body data, the BCB for that security-target MUST specify, as part of the cipher suite @@ -659,614 +691,456 @@ o The BCB's "discard" flag may be set independently from its security-target's "discard" flag. Whether or not the BCB's "discard" flag is set is an implementation/policy decision for the encrypting node. (The "discard" flag is more properly called the "Discard if block cannot be processed" flag.) o A BCB MAY include information as part of additional authenticated data to address parts of the target block, such as EID references, that are not converted to cipher-text. -3.6. Cryptographic Message Syntax Block - - A CMSB is an ASB with the following additional restrictions: - - The block-type code value MUST be 0x04. - - The content of the block must contain valid CMS data, as defined - in [RFC5652] , and encoded in X.690 BER or DER encoding. - - The block processing control flags value can be set to whatever - values are required by local policy. This flag SHOULD NOT be set - otherwise. Cipher suite designers should carefully consider the - effect of setting flags that either discard the block or delete - the bundle in the event that this block cannot be processed. - - The security-target MUST uniquely identify a block within the - bundle. The reserved block type 0x01 specifies the singleton - payload block. - - The security operation(s) will be performed on the security-target - block's data and the resulting CMS content will be stored within - the CMSB block's security-result field. The security-target - block's data will then be removed. - - A CMSB block MAY include multiple CMS security operations within a - single block to allow for multiple nested operations to be - performed on a bundle block. Multiple CMSB blocks MAY be included - in a bundle as long as the security-target for each is unique. - - Key-information, if available, MUST appear within the CMS content - contained in the security-result field. - - A CMSB block is created with its corresponding security-target field - pointing to a unique bundle block. The CMS security operations are - performed upon the security-target's data field and the resulting - encoded CMS content is stored within the CMS security-result field of - the CMSB's payload. The security-target block's data MAY be left - intact, replaced with alternate data, or completely erased based on - the specification of the utilized CMS ciphersuite definition and - applicable policy. - - Multiple CMS operations may be nested within a single CMSB block to - allow more than one security operation to be performed upon a - security-target. - - CMS Operations can be considered to have BPSec parallels: CMSB - Enveloped-Data content type SHALL be considered as equivalent to a - BPSec BCB block, and a CMSB Signed-Data type SHALL be considered as - equivalent to a BPSec BIB block. - -3.7. Block Interactions +3.5. Block Interactions The security-block types defined in this specification are designed to be as independent as possible. However, there are some cases where security blocks may share a security-target creating processing dependencies. If confidentiality is being applied to a target that already has integrity applied to it, then an undesirable condition occurs where a security-aware intermediate node would be unable to check the integrity result of a block because the block contents have been encrypted after the integrity signature was generated. To address this concern, the following processing rules MUST be followed. o If confidentiality is to be applied to a target, it MUST also be - applied to every integrity operation already defined for that + applied to any integrity operation already defined for that target. This means that if a BCB is added to encrypt a block, another BCB MUST also be added to encrypt a BIB also targeting that block. o An integrity operation MUST NOT be applied to a security-target if a BCB in the bundle shares the same security-target. This prevents ambiguity in the order of evaluation when receiving a BIB and a BCB for a given security-target. o An integrity value MUST NOT be evaluated if the BIB providing the integrity value is the security target of an existing BCB block in the bundle. In such a case, the BIB data contains cipher-text as it has been encrypted. o An integrity value MUST NOT be evaluated if the security-target of the BIB is also the security-target of a BCB in the bundle. In such a case, the security-target data contains cipher-text as it has been encrypted. - o As mentioned in Section 3.5, a BIB MUST NOT have a BCB as its + o As mentioned in Section 3.3, a BIB MUST NOT have a BCB as its security target. BCBs may embed integrity results as part of cipher suite parameters. - o As mentioned in Section 4.4, CMS operations are considered to have - operational parallels. When a CMSB is used, these parallels MUST - be considered for block interactions (e.g., a Signed-Data - structure MUST NOT be evaluated if the security-target of the - operation is also the security-target of a BCB) - - o If a single bundle is going to contain a CMSB as well as other - security blocks, the CMS operations MUST be performed and the CMSB - MUST be created before any other security operation is applied. - - Additionally, since the CMSB block may contain either integrity or - confidentiality information in its encapsulated CMS, there is no way - to evaluate conflicts when a BIB/BCB and a CMSB have the same - security target. To address this concern, the following processing - rules MUST be followed. - - o If an extension block is the target of a BIB or a BCB, then the - extension block MUST NOT also be the target of a CMSB, and vice- - versa. - - o Generally, a CMSB MUST be processed before any BIB or BCB blocks - are processed. - These restrictions on block interactions impose a necessary ordering when applying security operations within a bundle. Specifically, for a given security-target, BIBs MUST be added before BCBs. This ordering MUST be preserved in cases where the current BPA is adding all of the security blocks for the bundle or whether the BPA is a waypoint adding new security blocks to a bundle that already contains security blocks. -3.8. Parameters and Result Fields +3.6. Multi-Target Block Definitions + + A security-block MAY target multiple security-targets if and only if + all cipher suite parameters, security source, and key information are + common for each security operation. The following processing + directives apply for these multi-target blocks. + + o If a security-block has more than one security-target, then each + type identifier in the security result TLV MUST be interpretted as + a tuple with the first entry being the security-target for which + the security result applies and the second entry being the type + value enumeration of the security result value. + + o If the security-block has a single security-target, the type field + of every entry in the security result array MUST simply be the + type field and MUST NOT be a tuple as described above. + +3.7. Parameters and Result Fields Various cipher suites include several items in the cipher suite parameters and/or security-result fields. Which items MAY appear is defined by the particular cipher suite description. A cipher suite MAY support several instances of the same type within a single block. Each item is represented as a type-length-value. Type is a single byte indicating the item. Length is the count of data bytes to - follow, and is an SDNV-encoded integer. Value is the data content of - the item. + follow, and is an Unsigned Integer. Value is the data content of the + item. Item types, name, and descriptions are defined as follows. Cipher suite parameters and result fields. - +-------+----------------+------------------------------------------+ - | Type | Name | Description | - +-------+----------------+------------------------------------------+ - | 0 | Reserved | | - +-------+----------------+------------------------------------------+ - | 1 | Initialization | A random value, typically eight to | - | | Vector (IV) | sixteen bytes. | - +-------+----------------+------------------------------------------+ - | 2 | Reserved | | - +-------+----------------+------------------------------------------+ - | 3 | Key | Material encoded or protected by the key | - | | Information | management system and used to transport | - | | | an ephemeral key protected by a long- | - | | | term key. | - +-------+----------------+------------------------------------------+ - | 4 | Content Range | Pair of SDNV values (offset,length) | - | | | specifying the range of payload bytes to | - | | | which an operation applies. The offset | - | | | MUST be the offset within the original | - | | | bundle, even if the current bundle is a | - | | | fragment. | - +-------+----------------+------------------------------------------+ - | 5 | Integrity | Result of BAB or BIB digest or other | - | | Signatures | signing operation. | - +-------+----------------+------------------------------------------+ - | 6 | Unassigned | | - +-------+----------------+------------------------------------------+ - | 7 | Salt | An IV-like value used by certain | - | | | confidentiality suites. | - +-------+----------------+------------------------------------------+ - | 8 | BCB Integrity | Output from certain confidentiality | - | | Check Value | cipher suite operations to be used at | - | | (ICV) / | the destination to verify that the | - | | Authentication | protected data has not been modified. | - | | Tag | This value MAY contain padding if | - | | | required by the cipher suite. | - +-------+----------------+------------------------------------------+ - | 9-255 | Reserved | | - +-------+----------------+------------------------------------------+ + +-------+----------------+-----------------------------+------------+ + | Type | Name | Description | Field | + +-------+----------------+-----------------------------+------------+ + | 0 | Reserved | | | + +-------+----------------+-----------------------------+------------+ + | 1 | Initialization | A random value, typically | Cipher | + | | Vector (IV) | eight to sixteen bytes. | Suite | + | | | | Parameters | + +-------+----------------+-----------------------------+------------+ + | 2 | Reserved | | | + +-------+----------------+-----------------------------+------------+ + | 3 | Key | Material encoded or | Cipher | + | | Information | protected by the key | Suite | + | | | management system and used | Parameters | + | | | to transport an ephemeral | | + | | | key protected by a long- | | + | | | term key. | | + +-------+----------------+-----------------------------+------------+ + | 4 | Content Range | Pair of Unsigned Integers | Cipher | + | | | (offset,length) specifying | Suite | + | | | the range of payload bytes | Parameters | + | | | to which an operation | | + | | | applies. The offset MUST be | | + | | | the offset within the | | + | | | original bundle, even if | | + | | | the current bundle is a | | + | | | fragment. | | + +-------+----------------+-----------------------------+------------+ + | 5 | Integrity | Result of BAB or BIB digest | Security | + | | Signatures | or other signing operation. | Results | + +-------+----------------+-----------------------------+------------+ + | 6 | Unassigned | | | + +-------+----------------+-----------------------------+------------+ + | 7 | Salt | An IV-like value used by | Cipher | + | | | certain confidentiality | Suite | + | | | suites. | Parameters | + +-------+----------------+-----------------------------+------------+ + | 8 | BCB Integrity | Output from certain | Security | + | | Check Value | confidentiality cipher | Results | + | | (ICV) / | suite operations to be used | | + | | Authentication | at the destination to | | + | | Tag | verify that the protected | | + | | | data has not been modified. | | + | | | This value MAY contain | | + | | | padding if required by the | | + | | | cipher suite. | | + +-------+----------------+-----------------------------+------------+ + | 9-255 | Reserved | | | + +-------+----------------+-----------------------------+------------+ Table 1 -3.9. BSP Block Example +3.8. BSP Block Example An example of BPSec blocks applied to a bundle is illustrated in Figure 4. In this figure the first column represents blocks within a bundle and the second column represents a unique identifier for each block, suitable for use as the security-target of a BPSec security- block. Since the mechanism and format of a security-target is not specified in this document, the terminology B1...Bn is used to identify blocks in the bundle for the purposes of illustration. Block in Bundle ID - +=================================+====+ + +===================================+====+ | Primary Block | B1 | - +---------------------------------+----+ - | Lone BIB | B2 | + +-----------------------------------+----+ + | BIB | B2 | | OP(integrity, target=B1) | | - +---------------------------------+----+ - | Lone BCB | B3 | + +-----------------------------------+----+ + | BCB | B3 | | OP(confidentiality, target=B4) | | - +---------------------------------+----+ + +-----------------------------------+----+ | Extension Block | B4 | - +---------------------------------+----+ - | Lone BIB | B5 | + +-----------------------------------+----+ + | BIB | B5 | | OP(integrity, target=B6) | | - +---------------------------------+----+ + +-----------------------------------+----+ | Extension Block | B6 | - +---------------------------------+----+ - | Lone BCB | B7 | - | OP(confidentiality, target=B8) | | - +---------------------------------+----+ - | Lone BIB (encrypted by B7) | B8 | - | OP(integrity, target=B10) | | - +---------------------------------+----| - | Lone BCB | B9 | - | OP(confidentiality, target=B10) | | - +---------------------------------+----+ - | Payload Block |B10 | - +---------------------------------+----+ + +-----------------------------------+----+ + | BCB | B7 | + | OP(confidentiality,target=B8,B9) | | + +-----------------------------------+----+ + | BIB (encrypted by B7) | B8 | + | OP(integrity, target=B9) | | + +-----------------------------------+----| + | Payload Block | B9 | + +-----------------------------------+----+ Figure 4: Sample Use of BSP Blocks - In this example a bundle has five non-security-related blocks: the - primary block (B1), three extension blocks (B4,B6,B9), and a payload - block (B11). The following security applications are applied to this + In this example a bundle has four non-security-related blocks: the + primary block (B1), three extension blocks (B4,B6), and a payload + block (B9). The following security applications are applied to this bundle. o An integrity signature applied to the canonicalized primary block. This is accomplished by a single BIB (B2). o Confidentiality for the first extension block (B4). This is - accomplished by a single BCB block (B3). + accomplished by a BCB block (B3). o Integrity for the second extension block (B6). This is - accomplished by a single BIB block (B5). NOTE: If the extension - block B6 contains a representation of the serialized bundle (such - as a hash over all blocks in the bundle at the time of its last + accomplished by a BIB block (B5). NOTE: If the extension block B6 + contains a representation of the serialized bundle (such as a hash + over all blocks in the bundle at the time of its last transmission) then the BIB block is also providing an authentication service from the prior BPSEC-BPA to this BPSEC-BPA. o An integrity signature on the payload (B10). This is accomplished - by a single BIB block (B8). + by a BIB block (B8). o Confidentiality for the payload block and it's integrity - signature. This is accomplished by two Lone BCB blocks: B7 - encrypting B8, and B9 encrypting B10. - - Block in Bundle ID - +=========================================+====+ - | Primary Block | B1 | - +-----------------------------------------+----+ - | First BAB | B2 | - | OP(authentication, Bundle) | | - +-----------------------------------------+----+ - | Lone CMSB | B3 | - | security-target=0x01 | | - | security-result= | | - | | | - | Signed-Data { | | - | Digest Algorithm(s), | | - | Enveloped-Data { | | - | Encrypted Data, | | - | Encrypted Encryption Key(s) | | - | }, | | - | Signature(s) and Certificate Chain(s) | | - | } | | - | | | - +-----------------------------------------+----+ - | Payload Block | B4 | - | (Empty Data Field) | | - +-----------------------------------------+----+ - | Last BAB | B5 | - | OP(authentication, Bundle) | | - +-----------------------------------------+----+ - - Figure 5: Sample Bundle With CMS Block - - In this example a bundle has two non-security-related blocks: the - primary block (B1) and a payload block (B4). This method would allow - for the bundle to carry multiple CMS payloads by utilizing a multiple - CMSB ASBs. The following security applications are applied to this - bundle. - - o Authentication over the bundle. This is accomplished by two BAB - blocks: B2 and B5. - - o Encrypted and signed CMS content contained within the CMSB block. - The first CMS operation, encryption, is performed on the data - contained within the block the security-target points to, in this - case, the payload block. The resulting encrypted data is then - signed and the final CMS content is stored within the CMSB block's - security-result field. The payload block's data is subsequently - removed now that the original data has been encoded within the - CMSB block. - -4. Security Processing - - This section describes the security aspects of bundle processing. - -4.1. Canonical Forms - - In order to verify a signature of a block, the exact same bits, in - the exact same order, MUST be input to the calculation upon - verification as were input upon initial computation of the original - signature value. - - Many fields in various blocks are stored as variable-length SDNVs. - These are canonicalized into an "unpacked form" as eight-byte fixed- - width fields in network byte order. - -4.1.1. Block Canonicalization - - This algorithm protects those parts of a block that SHOULD NOT be - changed in transit. + signature. This is accomplished by a BCB block, B7, encrypting B8 + and B9. - There are three types of blocks that may undergo block - canonicalization: the primary block, the payload block, or an - extension block. +4. Canonical Forms -4.1.1.1. Primary Block Canonicalization + By definition, an integrity service determines whether any aspect of + a block was changed from the moment the security service was applied + at the security source until the point of current evaluation. To + successfully verify the integrity of a block, the data passed to the + verifying cipher suite MUST be the same bits, in the same order, as + those passed to the signature-generating cipher suite at the security + source. - The canonical form of the primary block is shown in Figure 6. - Essentially, it de-references the dictionary block, adjusts lengths - where necessary, and ignores flags that may change in transit. + However, [BPBIS] does not specify a single on-the-wire encoding of + bundles. In cases where a security source generates a different + encoding than that used at a receiving node, care MUST be taken to + ensure that the inputs to cipher suites at the receiving node is a + bitwise match to inputs provided at the security source. - +----------------+----------------+----------------+----------------+ - | Version | Processing flags (incl. COS and SRR) | - +----------------+----------------+---------------------------------+ - | Canonical primary block length | - +----------------+----------------+---------------------------------+ - | Destination endpoint ID length | - +----------------+----------------+---------------------------------+ - | Destination endpoint ID | - +----------------+----------------+---------------------------------+ - | Source endpoint ID length | - +----------------+----------------+----------------+----------------+ - | Source endpoint ID | - +----------------+----------------+---------------------------------+ - | Report-to endpoint ID length | - +----------------+----------------+----------------+----------------+ - | Report-to endpoint ID | - +----------------+----------------+----------------+----------------+ - + Creation Timestamp (2 x SDNV) + - +---------------------------------+---------------------------------+ - | Lifetime | - +----------------+----------------+----------------+----------------+ + This section provides guidance on how to create a canonical form for + each type of block in a bundle. This form MUST be used when + generating inputs to cipher suites for use by BPSec blocks. - Figure 6: The Canonical Form of the Primary Bundle Block + This specification does not define any security operation over the + entire bundle and, therefore, provides no canonical form for a + serialized bundle. - The fields shown in Figure 6 are as follows: +4.1. Technical Notes - o The version value is the single-byte value in the primary block. + The following technical considerations hold for all canonicalizations + in this section. - o The processing flags value in the primary block is an SDNV, and - includes the class-of-service (COS) and status report request - (SRR) fields. For purposes of canonicalization, the unpacked SDNV - is ANDed with mask 0x0000 0000 0007 C1BE to set to zero all - reserved bits and the "bundle is a fragment" bit. + o Any numeric fields defined as variable-length MUST be expanded to + their "unpacked" form. For example, a 32-bit integer value MUST + be unpacked to a four-byte representation. - o The canonical primary block length value is a four-byte value - containing the length (in bytes) of this structure, in network - byte order. + o Each block encoding MUST follow the CBOR encodings provided in + [BPBISCBOR]. - o The destination endpoint ID length and value are the length (as a - four-byte value in network byte order) and value of the - destination endpoint ID from the primary bundle block. The URI is - simply copied from the relevant part(s) of the dictionary block - and is not itself canonicalized. Although the dictionary entries - contain "null-terminators", the null-terminators are not included - in the length or the canonicalization. + o Canonical forms are not transmitted, they are used to generate + input to a cipher suite for secuity processing at a security-aware + node. - o The source endpoint ID length and value are handled similarly to - the destination. + o Reserved flags MUST NOT be included in any canonicalization as it + is not known if those flags will chaneg in transit. - o The report-to endpoint ID length and value are handled similarly - to the destination. + o These canonicalization algorithms assume that endpoint IDs + themselves are immutable and they are unsuitable for use in + environments where that assumption might be violated. - o The unpacked SDNVs for the creation timestamp and lifetime are - copied from the primary block. + o Cipher suites MAY define their own canonicalization algorithms and + require the use of those algorithms over the ones provided in this + specification. In the event of conflicting canonicalization + algorithms, cipher suite algorithms take precedence over this + specification. - o Fragment offset and total application data unit length are - ignored, as is the case for the "bundle is a fragment" bit - mentioned above. If the payload data to be canonicalized is less - than the complete, original bundle payload, the offset and length - are specified in the cipher suite parameters. +4.2. Primary Block Canonicalization -4.1.1.2. Payload Block Canonicalization + The primary block canonical form is the same as the CBOR encoding of + the block, with certain modifications to account for allowed block + changes as the bundle traverses the DTN. The fields that compromise + the primary block, and any special considerations for their + representation in a canonical form, are as follows. - When canonicalizing the payload block, the block processing control - flags value used for canonicalization is the unpacked SDNV value with - reserved and mutable bits masked to zero. The unpacked value is - ANDed with mask 0x0000 0000 0000 0077 to zero reserved bits and the - "last block" bit. The "last block" bit is ignored because BABs and - other security blocks MAY be added for some parts of the journey but - not others, so the setting of this bit might change from hop to hop. + o The Version field is included, without modification. - Payload blocks are canonicalized as-is, with the exception that, in - some instances, only a portion of the payload data is to be - protected. In such a case, only those bytes are included in the - canonical form, and additional cipher suite parameters are required - to specify which part of the payload is protected, as discussed - further below. + o The Bundle Processing Flags field is used, with modification. + Certain bundle processing flags MAY change as a bundle transits + the DTN without indicating an integrity error. These flags, which + are identified below, MUST NOT be represented in the canonicalized + form of the bundle processing flags and, instead, be represented + by the bit 0. -4.1.1.3. Extension Block Canonicalization + * Reserved flags. - When canonicalizing an extension block, the block processing control - flags value used for canonicalization is the unpacked SDNV value with - reserved and mutable bits masked to zero. The unpacked value is - ANDed with mask 0x0000 0000 0000 0057 to zero reserved bits, the - "last block" flag and the "Block was forwarded without being - processed" bit. The "last block" flag is ignored because BABs and - other security blocks MAY be added for some parts of the journey but - not others, so the setting of this bit might change from hop to hop. + * Bundle is a Fragment flag. - The "Block was forwarded without being processed" flag is ignored - because the bundle may pass through nodes that do not understand that - extension block and this flag would be set. + o The CRC Type, Destination EID, Source Node ID, Report-To EID, + Creation Timestamp, and Lifetime fields are included, without + modification. - Endpoint ID references in blocks are canonicalized using the de- - referenced text form in place of the reference pair. The reference - count is not included, nor is the length of the endpoint ID text. + o The fragment ID field MAY change if the bundle is fragmented in + transit and, as such, this field MUST NOT be included in the + canonicalization. - The EID reference is, therefore, canonicalized as :, - which includes the ":" character. + o The CRC field MAY change at each hop - for example, if a bundle + becomes fragmented, each fragment will have a different CRC value + from the original signed primary block. As such, this field MUST + NOT be included in the canonicalization. - Since neither the length of the canonicalized EID text nor a null- - terminator is used in EID canonicalization, a separator token MUST be - used to determine when one EID ends and another begins. When - multiple EIDs are canonicalized together, the character "," SHALL be - placed between adjacent instances of EID text. +4.3. Non-Primary-Block Canonicalization - The block-length is canonicalized as its unpacked SDNV value. If the - data to be canonicalized is less than the complete, original block - data, this field contains the size of the data being canonicalized - (the "effective block") rather than the actual size of the block. + All non-primary blocks (NPBs) in [BPBIS] share the same block + structure and should be canonicalized in the same way. -4.1.2. Considerations + Canonicalization for NPBs is dependent on whether the security + operation being performed is integrity or confidentiality. Integrity + operations consider every field in the block, whereas confidentiality + operations only consider the block-type-specific data. Since + confidentiality is applied to hide information (replacing plaintext + with ciphertext) it provides no benefit to include in the + confidentiality calculation information that MUST remain readable, + such as block fields other than the block-type-specific data. - o The canonical forms for the bundle and various extension blocks is - not transmitted. It is simply an artifact used as input to - digesting. + The fields that comprise a NPB, and any special considerations for + their representation in a canonical form, are as follows. - o We omit the reserved flags because we cannot determine if they - will change in transit. The masks specified above will have to be - revised if additional flags are defined and they need to be - protected. + o The Block Type Code field is included, without modification, for + integrity operations and omitted for confidentiality operations. - o All SDNV fields here are canonicalized as eight-byte unpacked - values in network byte order. Length fields are canonicalized as - four-byte values in network byte order. Encoding does not need - optimization since the values are never sent over the network. + o The Block Number field is included, without modification, for + integrity operations and omitted for confidentiality operations. - o These canonicalization algorithms assume that endpoint IDs - themselves are immutable and they are unsuitable for use in - environments where that assumption might be violated. + o The Block Processing Control Flags field is included, without + modification, for integrity operations and omitted for + confidentiality operations, with the exception of reserved flags + which are treated as 0 in both cases. - o Cipher suites MAY define their own canonicalization algorithms and - require the use of those algorithms over the ones provided in this - specification. + o The CRC type and CRC fields are included, without modification, + for integrity operations and omitted for confidentiality + operations. -4.2. Endpoint ID Confidentiality + o The Block Type Specific Data field is included, without + modification, for both integrity and confidentiality operations, + with the exception that in some cases only a portion of the + payload data is to be processed. In such a case, only those bytes + are included in the canonical form and additional cipher suite + parameters are required to specify which part of the field is + included. - Every bundle has a primary block that contains the source and - destination endpoint IDs, and possibly other EIDs (in the dictionary - field) that cannot be encrypted. If endpoint ID confidentiality is - required, then bundle-in-bundle encapsulation can solve this problem - in some instances. +5. Security Processing - Similarly, confidentiality requirements MAY also apply to other parts - of the primary block (e.g., the current-custodian), and that is - supported in the same manner. + This section describes the security aspects of bundle processing. -4.3. Bundles Received from Other Nodes +5.1. Bundles Received from Other Nodes Security blocks MUST be processed in a specific order when received by a security-aware node. The processing order is as follows. o All BCB blocks in the bundle MUST be evaluated prior to evaluating any BIBs in the bundle. When BIBs and BCBs share a security- target, BCBs MUST be evaluated first and BIBs second. -4.3.1. Receiving BCB Blocks +5.1.1. Receiving BCB Blocks - If the bundle has a BCB and the receiving node is the destination for - the bundle, the node MUST decrypt the relevant parts of the security- - target in accordance with the cipher suite specification. + If a received bundle contains a BCB, the receiving node MUST + determine whether it has the responsibility of decrypting the BCB + security target and removing the BCB prior to delivering data to an + application at the node or forwarding the bundle. - If the relevant parts of an encrypted payload cannot be decrypted - (i.e., the decryption key cannot be deduced or decryption fails), - then the bundle MUST be discarded and processed no further; in this - case, a bundle deletion status report (see [BPBIS]) indicating the - decryption failure MAY be generated. If any other encrypted - security-target cannot be decrypted then the associated security- - target and all security blocks associated with that target MUST be - discarded and processed no further. + If the receiving node is the destination of the bundle, the node MUST + decrypt any BCBs remaining in the bundle. If the receiving node is + not the destination of the bundle, the node MAY decrypt the BCB if + directed to do so as a matter of security policy. + + If the relevant parts of an encrypted payload block cannot be + decrypted (i.e., the decryption key cannot be deduced or decryption + fails), then the bundle MUST be discarded and processed no further. + If an encrypted security-target other than the payload block cannot + be decrypted then the associated security-target and all security + blocks associated with that target MUST be discarded and processed no + further. In both cases, requested status reports (see [BPBIS]) MAY + be generated to reflect bundle or block deletion. When a BCB is decrypted, the recovered plain-text MUST replace the cipher-text in the security-target body data -4.3.2. Receiving BIB Blocks + If a BCB contains multiple security-targets, all security-targets + MUST be processed if the BCB is processed by the Node. The effect of + this is to be the same as if each security-target had been + represented by an individual BCB with a single security-target. + +5.1.2. Receiving BIB Blocks + + If a received bundle contains a BIB, the receiving node MUST + determine whether it has the responsibility of verifying the BIB + security target and whether to remove the BIB prior to delivering + data to an application at the node or forwarding the bundle. A BIB MUST NOT be processed if the security-target of the BIB is also the security-target of a BCB in the bundle. Given the order of operations mandated by this specification, when both a BIB and a BCB share a security-target, it means that the security-target MUST have been encrypted after it was integrity signed and, therefore, the BIB cannot be verified until the security-target has been decrypted by processing the BCB. If the security policy of a security-aware node specifies that a - bundle SHOULD apply integrity to a specific security-target and no - such BIB is present in the bundle, then the node MUST process this - security-target in accordance with the security policy. This MAY - involve removing the security-target from the bundle. If the removed - security-target is the payload or primary block, the bundle MAY be - discarded. This action may occur at any node that has the ability to - verify an integrity signature, not just the bundle destination. + bundle should have applied integrity to a specific security-target + and no such BIB is present in the bundle, then the node MUST process + this security-target in accordance with the security policy. This + MAY involve removing the security-target from the bundle. If the + removed security-target is the payload or primary block, the bundle + MAY be discarded. This action may occur at any node that has the + ability to verify an integrity signature, not just the bundle + destination. If the bundle has a BIB and the receiving node is the destination for the bundle, the node MUST verify the security-target in accordance with the cipher suite specification. If a BIB check fails, the security-target has failed to authenticate and the security-target SHALL be processed according to the security policy. A bundle status report indicating the failure MAY be generated. Otherwise, if the BIB verifies, the security-target is ready to be processed for delivery. If the bundle has a BIB and the receiving node is not the bundle destination, the receiving node MAY attempt to verify the value in the security-result field. If the check fails, the node SHALL process the security-target in accordance to local security policy. It is RECOMMENDED that if a payload integrity check fails at a waypoint that it is processed in the same way as if the check fails at the destination. -4.4. Receiving CMSB Blocks - - A CMSB MUST NOT be processed if its security target is also the - security target of any BIB or BCB in the bundle. - - The security services provided by a CMSB will be considered - successful if all services in the CMSB are validated. If any one - service encapsulated in the CMSB fails to validate, then the CMSB - MUST be considered as having failed to validate and MUST be - dispositioned in accordance with security policy. + If a BIB contains multiple security-targets, all security-targets + MUST be processed if the BIB is processed by the Node. The effect of + this is to be the same as if each security-target had been + represented by an individual BIB with a single security-target. -4.5. Bundle Fragmentation and Reassembly +5.2. Bundle Fragmentation and Reassembly If it is necessary for a node to fragment a bundle and security services have been applied to that bundle, the fragmentation rules described in [BPBIS] MUST be followed. As defined there and repeated here for completeness, only the payload may be fragmented; security - blocks, like all extension blocks, can never be fragmented. In - addition, the following security-specific processing is REQUIRED: + blocks, like all extension blocks, can never be fragmented. - o Due to the complexity of bundle fragmentation, including the + Due to the complexity of bundle fragmentation, including the possibility of fragmenting bundle fragments, integrity and confidentiality operations are not to be applied to a bundle - fragment. Specifically, a BCB or BIB MUST NOT be added to a - bundle fragment, even if the security-target of the security block - is not the payload. When integrity and confidentiality must be - applied to a fragment, we RECOMMEND that encapsulation be used - instead. - - o The authentication security policy requirements for a bundle MUST - be applied individually to all the bundles resulting from a - fragmentation event. - - o The decision to fragment a bundle MUST be made prior to adding - authentication to the bundle. The bundle MUST first be fragmented - and authentication applied to each individual fragment. - -4.6. Reactive Fragmentation - - When a partial bundle has been received, the receiving node SHALL - consult its security policy to determine if it MAY fragment the - bundle, converting the received portion into a bundle fragment for - further forwarding. Whether or not reactive fragmentation is - permitted SHALL depend on the security policy and the cipher suite - used to calculate the BAB authentication information, if required. - - Specifically, if the security policy does not require authentication, - then reactive fragmentation MAY be permitted. If the security policy - does require authentication, then reactive fragmentation MUST NOT be - permitted if the partial bundle is not sufficient to allow - authentication. - - If reactive fragmentation is allowed, then all BAB blocks must be - removed from created fragments. + representing a fragment (i.e., a bundle whose "bundle is a Fragment" + flag is set in the Bundle Processing Control Flags field). + Specifically, a BCB or BIB MUST NOT be added to a bundle fragment, + even if the security-target of the security block is not the payload. + When integrity and confidentiality must be applied to a fragment, we + RECOMMEND that encapsulation be used instead. -5. Key Management +6. Key Management Key management in delay-tolerant networks is recognized as a difficult topic and is one that this specification does not attempt to solve. -6. Policy Considerations +7. Policy Considerations When implementing BPSec, several policy decisions must be considered. This section describes key policies that affect the generation, forwarding, and receipt of bundles that are secured using this specification. o If a bundle is received that contains more than one security- operation, in violation of BPSec, then the BPA must determine how to handle this bundle. The bundle may be discarded, the block affected by the security-operation may be discarded, or one @@ -1285,81 +1159,304 @@ operation, or some other action. o It is recommended that security operations only be applied to the payload block, the primary block, and any block-types specifically identified in the security policy. If a BPA were to apply security operations such as integrity or confidentiality to every block in the bundle, regardless of the block type, there could be downstream errors processing blocks whose contents must be inspected at every hop in the network path. -7. Security Considerations - - Certain applications of DTN need to both sign and encrypt a message, - and there are security issues to consider with this. - - o To provide an assurance that a security-target came from a - specific source and has not been changed, then it should be signed - with a BIB. - - o To ensure that a security-target cannot be inspected during - transit, it should be encrypted with a BCB. - o Adding a BIB to a security-target that has already been encrypted by a BCB is not allowed. Therefore, we recommend three methods to add an integrity signature to an encrypted security-target. - First, at the time of encryption, an integrity signature may be + + 1. At the time of encryption, an integrity signature may be generated and added to the BCB for the security-target as - additional information in the security-result field. Second, the - encrypted block may be replicated as a new block and integrity - signed. Third, an encapsulation scheme may be applied to - encapsulate the security-target (or the entire bundle) such that - the encapsulating structure is, itself, no longer the security- - target of a BCB and may therefore be the security-target of a BIB. + additional information in the security-result field. -8. Conformance + 2. The encrypted block may be replicated as a new block and + integrity signed. + + 3. An encapsulation scheme may be applied to encapsulate the + security-target (or the entire bundle) such that the + encapsulating structure is, itself, no longer the security- + target of a BCB and may therefore be the security-target of a + BIB. + +8. Security Considerations + + Given the nature of delay-tolerant networking applications, it is + expected that bundles may traverse a variety of environments and + devices which each pose unique security risks and requirements on the + implementation of security within BPSEC. For these reasons, it is + important to introduce key threat models and describe the roles and + responsibilities of the BPSEC protocol in protecting the + confidentiality and integrity of the data against those threats + throughout the DTN. This section provides additional discussion on + security threats that BPSEC will face and describe in additional + detail how BPSEC security mechanisms operate to mitigate these + threats. + + It should be noted that BPSEC addresses only the security of data + traveling over the DTN, not the underlying DTN itself. Additionally, + BPSEC addresses neither the fitness of externally-defined + cryptographic methods nor the security of their implementation. It + is the responsibility of the BPSEC implementer that appropriate + algorithms and methods are chosen. Furthermore, the BPSEC protocol + does not address threats which share computing resources with the DTN + and/or BPSEC software implementations. These threats may be + malicious software or compromised libraries which intend to intercept + data or recover cryptographic material. Here, it is the + responsibility of the BPSEC implementer to ensure that any + cryptographic material, including shared secret or private keys, is + protected against access within both memory and storage devices. + + The threat model described here is assumed to have a set of + capabilities identical to those described by the Internet Threat + Model in [RFC3552], but the BPSEC threat model is scoped to + illustrate threats specific to BPSEC operating within DTN + environments and therefore focuses on man-in-the-middle (MITM) + attackers. + +8.1. Attacker Capabilities and Objectives + + BPSEC was designed to protect against MITM threats which may have + access to a bundle during transit from its source, Alice, to its + destination, Bob. A MITM node, Mallory, is a non-cooperative node + operating on the DTN between Alice and Bob that has the ability to + receive bundles, examine bundles, modify bundles, forward bundles, + and generate bundles at will in order to compromise the + confidentiality or integrity of data within the DTN. For the + purposes of this section, any MITM node is assumed to effectively be + security-aware even if it does not implement the BPSec protocol. + There are three classes of MITM nodes which are differentiated based + on their access to cryptographic material: + + o Unprivileged Node: Mallory has not been provisioned within the + secure environment and only has access to cryptographic material + which has been publicly-shared. + + o Legitimate Node: Mallory is within the secure environment and + therefore has access to cryptographic material which has been + provisioned to Mallory (i.e., K_M) as well as material which has + been publicly-shared. + + o Privileged Node: Mallory is a privileged node within the secure + environment and therefore has access to cryptographic material + which has been provisioned to Mallory, Alice and/or Bob (i.e. + K_M, K_A, and/or K_B) as well as material which has been publicly- + shared. + + If Mallory is operating as a privileged node, this is tantamount to + compromise; BPSec does not provide mechanisms to detect or remove + Mallory from the DTN or BPSec secure environment. It is up to the + BPSec implementer or the underlying cryptographic mechanisms to + provide appropriate capabilities if they are needed. It should also + be noted that if the implementation of BPSec uses a single set of + shared cryptographic material for all nodes, a legitimate node is + equivalent to a privileged node because K_M == K_A == K_B. + + A special case of the legitimate node is when Mallory is either Alice + or Bob (i.e., K_M == K_A or K_M == K_B). In this case, Mallory is + able to impersonate traffic as either Alice or Bob, which means that + traffic to and from that node can be decrypted and encrypted, + respectively. Additionally, messages may be signed as originating + from one of the endpoints. + +8.2. Attacker Behaviors and BPSec Mitigations + +8.2.1. Eavesdropping Attacks + + Once Mallory has received a bundle, she is able to examine the + contents of that bundle and attempt to recover any protected data or + cryptographic keying material from the blocks contained within. The + protection mechanism that BPSec provides against this action is the + BCB, which encrypts the contents of its security-target, providing + confidentiality of the data. Of course, it should be assumed that + Mallory is able to attempt offline recovery of encrypted data, so the + cryptographic mechanisms selected to protect the data should provide + a suitable level of protection. + + When evaluating the risk of eavesdropping attacks, it is important to + consider the lifetime of bundles on a DTN. Depending on the network, + bundles may persist for days or even years. If a bundle does persist + on the network for years and the cipher suite used for a BCB provides + inadequate protection, Mallory may be able to recover the protected + data before that bundle reaches its intended destination. + +8.2.2. Modification Attacks + + As a node participating in the DTN between Alice and Bob, Mallory + will also be able to modify the received bundle, including non-BPSec + data such as the primary block, payload blocks, or block processing + control flags as defined in [BPBIS]. Mallory will be able to + undertake activities which include modification of data within the + blocks, replacement of blocks, addition of blocks, or removal of + blocks. Within BPSec, both the BIB and BCB provide integrity + protection mechanisms to detect or prevent data manipulation attempts + by Mallory. + + The BIB provides that protection to another block which is its + security-target. The cryptographic mechansims used to generate the + BIB should be strong against collision attacks and Mallory should not + have access to the cryptographic material used by the originating + node to generate the BIB (e.g., K_A). If both of these conditions + are true, Mallory will be unable to modify the security-target or the + BIB and lead Bob to validate the security-target as originating from + Alice. + + Since BPSec security operations are implemented by placing blocks in + a bundle, there is no in-band mechanism for detecting or correcting + certain cases where Mallory removes blocks from a bundle. If Mallory + removes a BCB block, but keeps the security-target, the security- + target remains encrypted and there is a possibility that there may no + longer be sufficient information to decrypt the block at its + destination. If Mallory removes both a BCB (or BIB) and its + security-target there is no evidence left in the bundle of the + security operation. Similarly, if Mallory removes the BIB but not + the security-target there is no evidence left in the bundle of the + security operation. In each of these cases, the implementation of + BPSec MUST be combined with policy configuration at endpoints in the + network which describe the expected and required security operations + that must be applied on transmission and are expected to be present + on receipt. This or other similar out-of-band information is + required to correct for removal of security information in the + bundle. + + A limitation of the BIB may exist within the implementation of BIB + validation at the destination node. If Mallory is a legitimate node + within the DTN, the BIB generated by Alice with K_A can be replaced + with a new BIB generated with K_M and forwarded to Bob. If Bob is + only validating that the BIB was generated by a legitimate user, Bob + will acknowledge the message as originating from Mallory instead of + Alice. In order to provide verifiable integrity checks, both a BIB + and BCB should be used. Alice creates a BIB with the protected data + block as the security-target and then creates a BCB with both the BIB + and protected data block as its security-targets. In this + configuration, since Mallory is only a legitimate node and does not + have access to Alice's key K_A, Mallory is unable to decrypt the BCB + and replace the BIB. + +8.2.3. Topology Attacks + + If Mallory is in a MITM position within the DTN, she is able to + influence how any bundles that come to her may pass through the + network. Upon receiving and processing a bundle that must be routed + elsewhere in the network, Mallory has three options as to how to + proceed: not forward the bundle, forward the bundle as intended, or + forward the bundle to one or more specific nodes within the network. + + Attacks that involve re-routing the packets throughout the network + are essentially a special case of the modification attacks described + in this section where the attacker is modifying fields within the + primary block of the bundle. Given that BPSec cannot encrypt the + contents of the primary block, alternate methods must be used to + prevent this situation. These methods MAY include requiring BIBs for + primary blocks, using encapsulation, or otherwise strategically + manipulating primary block data. The specifics of any such + mitigation technique are specific to the implementation of the + deploying network and outside of the scope of this document. + + Furthermore, routing rules and policies may be useful in enforcing + particular traffic flows to prevent topology attacks. While these + rules and policies may utilize some features provided by BPSec, their + definition is beyond the scope of this specification. + +8.2.4. Message Injection + + Mallory is also able to generate new bundles and transmit them into + the DTN at will. These bundles may either be copies or slight + modifications of previously-observed bundles (i.e., a replay attack) + or entirely new bundles generated based on the Bundle Protocol, + BPSec, or other bundle-related protocols. With these attacks + Mallory's objectives may vary, but may be targeting either the bundle + protocol or application-layer protocols conveyed by the bundle + protocol. + + BPSec relies on cipher suite capabilities to prevent replay or forged + message attacks. A BCB used with appropriate cryptographic + mechanisms (e.g., a counter-based cipher mode) may provide replay + protection under certain circumstances. Alternatively, application + data itself may be augmented to include mechanisms to assert data + uniqueness and then protected with a BIB, a BCB, or both along with + other block data. In such a case, the receiving node would be able + to validate the uniqueness of the data. + +9. Ciphersuite Authorship Considerations + + Cipher suite developers or implementers should consider the diverse + performance and conditions of networks on which the Bundle Protocol + (and therefore BPSec) will operate. Specifically, the delay and + capacity of delay-tolerant networks can vary substantially. Cipher + suite developers should consider these conditions to better describe + the conditions when those suites will operate or exhibit + vulnerability, and selection of these suites for implementation + should be made with consideration to the reality. There are key + differences that may limit the opportunity to leverage existing + cipher suites and technologies that have been developed for use in + traditional, more reliable networks: + + o Data Lifetime: Depending on the application environment, bundles + may persist on the network for extended periods of time, perhaps + even years. Cryptographic algorithms should be selected to ensure + protection of data against attacks for a length of time reasonable + for the application. + + o One-Way Traffic: Depending on the application environment, it is + possible that only a one-way connection may exist between two + endpoints, or if a two-way connection does exist, the round-trip + time may be extremely large. This may limit the utility of + session key generation mechanisms, such as Diffie-Hellman, as a + two-way handshake may not be feasible or reliable. + + o Opportunistic Access: Depending on the application environment, a + given endpoint may not be guaranteed to be accessible within a + certain amount of time. This may make asymmetric cryptographic + architectures which rely on a key distribution center or other + trust center impractical under certain conditions. + +10. Conformance All implementations are strongly RECOMMENDED to provide some method of hop-by-hop verification by generating a hash to some canonical form of the bundle and placing an integrity signature on that form using a BIB. -9. IANA Considerations +11. IANA Considerations This protocol has fields that have been registered by IANA. -9.1. Bundle Block Types +11.1. Bundle Block Types This specification allocates three block types from the existing "Bundle Block Types" registry defined in [RFC6255] . Additional Entries for the Bundle Block-Type Codes Registry: +-------+-----------------------------+---------------+ | Value | Description | Reference | +-------+-----------------------------+---------------+ | 2 | Block Integrity Block | This document | | 3 | Block Confidentiality Block | This document | - | 4 | CMS Block | This document | +-------+-----------------------------+---------------+ Table 2 -9.2. Cipher Suite Flags +11.2. Cipher Suite Flags This protocol has a cipher suite flags field and certain flags are defined. An IANA registry has been set up as follows. The registration policy for this registry is: Specification Required The Value range is: Variable Length - Cipher Suite Flag Registry: +--------------------------+-------------------------+--------------+ | Bit Position (right to | Description | Reference | | left) | | | +--------------------------+-------------------------+--------------+ | 0 | Block contains result | This | | | | document | | 1 | Block Contains | This | | | parameters | document | @@ -1364,71 +1461,77 @@ | 1 | Block Contains | This | | | parameters | document | | 2 | Source EID ref present | This | | | | document | | >3 | Reserved | This | | | | document | +--------------------------+-------------------------+--------------+ Table 3 -9.3. Parameters and Results +11.3. Parameters and Results This protocol has fields for cipher suite parameters and results. The field is a type-length-value triple and a registry is required for the "type" sub-field. The values for "type" apply to both the cipher suite parameters and the cipher suite results fields. Certain values are defined. An IANA registry has been set up as follows. The registration policy for this registry is: Specification Required The Value range is: 8-bit unsigned integer. Cipher Suite Parameters and Results Type Registry: - +---------+---------------------------------+---------------+ + +---------+-------------------------------------------+-------------+ | Value | Description | Reference | - +---------+---------------------------------+---------------+ - | 0 | reserved | This document | - | 1 | initialization vector (IV) | This document | - | 2 | reserved | This document | - | 3 | key-information | This document | - | 4 | content-range (pair of SDNVs) | This document | - | 5 | integrity signature | This document | - | 6 | unassigned | This document | - | 7 | salt | This document | - | 8 | BCB integrity check value (ICV) | This document | - | 9-191 | reserved | This document | - | 192-250 | private use | This document | - | 251-255 | reserved | This document | - +---------+---------------------------------+---------------+ + +---------+-------------------------------------------+-------------+ + | 0 | reserved | Section 3.7 | + | 1 | initialization vector (IV) | Section 3.7 | + | 2 | reserved | Section 3.7 | + | 3 | key-information | Section 3.7 | + | 4 | content-range (pair of Unsigned Integers) | Section 3.7 | + | 5 | integrity signature | Section 3.7 | + | 6 | unassigned | Section 3.7 | + | 7 | salt | Section 3.7 | + | 8 | BCB integrity check value (ICV) | Section 3.7 | + | 9-191 | reserved | Section 3.7 | + | 192-250 | private use | Section 3.7 | + | 251-255 | reserved | Section 3.7 | + +---------+-------------------------------------------+-------------+ Table 4 -10. References +12. References -10.1. Normative References +12.1. Normative References [BPBIS] Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol", - draft-ietf-dtn-bpbis-03 (work in progress), March 2016. + draft-ietf-dtn-bpbis-04 (work in progress), July 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. - [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, - RFC 5652, DOI 10.17487/RFC5652, September 2009, - . + [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC + Text on Security Considerations", BCP 72, RFC 3552, + DOI 10.17487/RFC3552, July 2003, + . [RFC6255] Blanchet, M., "Delay-Tolerant Networking Bundle Protocol IANA Registries", RFC 6255, May 2011. -10.2. Informative References +12.2. Informative References + + [BPBISCBOR] + Burleigh, S., "Bundle Protocol CBOR Representation + Specification", draft-burleigh-dtn-rs-cbor-01 (work in + progress), April 2016. [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant Networking Architecture", RFC 4838, April 2007. [RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell, "Bundle Security Protocol Specification", RFC 6257, May 2011. [SBSP] Birrane, E., "Streamlined Bundle Security Protocol", @@ -1448,26 +1551,18 @@ Edward J. Birrane, III The Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd. Laurel, MD 20723 US Phone: +1 443 778 7423 Email: Edward.Birrane@jhuapl.edu - Jeremy Pierce-Mayer - INSYEN AG - Muenchner Str. 20 - Oberpfaffenhofen, Bavaria DE - Germany - - Phone: +49 08153 28 2774 - Email: jeremy.mayer@insyen.com - Dennis C. Iannicca - NASA Glenn Research Center - 21000 Brookpark Rd. - Brook Park, OH 44135 + Kenneth McKeever + The Johns Hopkins University Applied Physics Laboratory + 11100 Johns Hopkins Rd. + Laurel, MD 20723 US - Phone: +1-216-433-6493 - Email: dennis.c.iannicca@nasa.gov + Phone: +1 443 778 2237 + Email: Ken.McKeever@jhuapl.edu