draft-ietf-dtn-bpsec-18.txt   draft-ietf-dtn-bpsec-19.txt 
Delay-Tolerant Networking E. Birrane Delay-Tolerant Networking E. Birrane
Internet-Draft K. McKeever Internet-Draft K. McKeever
Intended status: Standards Track JHU/APL Intended status: Standards Track JHU/APL
Expires: July 30, 2020 January 27, 2020 Expires: August 10, 2020 February 7, 2020
Bundle Protocol Security Specification Bundle Protocol Security Specification
draft-ietf-dtn-bpsec-18 draft-ietf-dtn-bpsec-19
Abstract Abstract
This document defines a security protocol providing end to end data This document defines a security protocol providing data integrity
integrity and confidentiality services for the Bundle Protocol. and confidentiality services for the Bundle Protocol.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 30, 2020. This Internet-Draft will expire on August 10, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2. Design Decisions . . . . . . . . . . . . . . . . . . . . . . 7 2. Design Decisions . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Block-Level Granularity . . . . . . . . . . . . . . . . . 7 2.1. Block-Level Granularity . . . . . . . . . . . . . . . . . 7
2.2. Multiple Security Sources . . . . . . . . . . . . . . . . 8 2.2. Multiple Security Sources . . . . . . . . . . . . . . . . 8
2.3. Mixed Security Policy . . . . . . . . . . . . . . . . . . 8 2.3. Mixed Security Policy . . . . . . . . . . . . . . . . . . 8
2.4. User-Defined Security Contexts . . . . . . . . . . . . . 9 2.4. User-Defined Security Contexts . . . . . . . . . . . . . 9
2.5. Deterministic Processing . . . . . . . . . . . . . . . . 9 2.5. Deterministic Processing . . . . . . . . . . . . . . . . 9
3. Security Blocks . . . . . . . . . . . . . . . . . . . . . . . 9 3. Security Blocks . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Block Definitions . . . . . . . . . . . . . . . . . . . . 9 3.1. Block Definitions . . . . . . . . . . . . . . . . . . . . 9
3.2. Uniqueness . . . . . . . . . . . . . . . . . . . . . . . 10 3.2. Uniqueness . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Target Multiplicity . . . . . . . . . . . . . . . . . . . 11 3.3. Target Multiplicity . . . . . . . . . . . . . . . . . . . 11
3.4. Target Identification . . . . . . . . . . . . . . . . . . 11 3.4. Target Identification . . . . . . . . . . . . . . . . . . 12
3.5. Block Representation . . . . . . . . . . . . . . . . . . 12 3.5. Block Representation . . . . . . . . . . . . . . . . . . 12
3.6. Abstract Security Block . . . . . . . . . . . . . . . . . 12 3.6. Abstract Security Block . . . . . . . . . . . . . . . . . 12
3.7. Block Integrity Block . . . . . . . . . . . . . . . . . . 15 3.7. Block Integrity Block . . . . . . . . . . . . . . . . . . 15
3.8. Block Confidentiality Block . . . . . . . . . . . . . . . 16 3.8. Block Confidentiality Block . . . . . . . . . . . . . . . 16
3.9. Block Interactions . . . . . . . . . . . . . . . . . . . 17 3.9. Block Interactions . . . . . . . . . . . . . . . . . . . 17
3.10. Parameter and Result Identification . . . . . . . . . . . 18 3.10. Parameter and Result Identification . . . . . . . . . . . 18
3.11. BSP Block Examples . . . . . . . . . . . . . . . . . . . 19 3.11. BSP Block Examples . . . . . . . . . . . . . . . . . . . 19
3.11.1. Example 1: Constructing a Bundle with Security . . . 19 3.11.1. Example 1: Constructing a Bundle with Security . . . 19
3.11.2. Example 2: Adding More Security At A New Node . . . 20 3.11.2. Example 2: Adding More Security At A New Node . . . 20
4. Canonical Forms . . . . . . . . . . . . . . . . . . . . . . . 22 4. Canonical Forms . . . . . . . . . . . . . . . . . . . . . . . 20
5. Security Processing . . . . . . . . . . . . . . . . . . . . . 22 5. Security Processing . . . . . . . . . . . . . . . . . . . . . 21
5.1. Bundles Received from Other Nodes . . . . . . . . . . . . 23 5.1. Bundles Received from Other Nodes . . . . . . . . . . . . 22
5.1.1. Receiving BCBs . . . . . . . . . . . . . . . . . . . 23 5.1.1. Receiving BCBs . . . . . . . . . . . . . . . . . . . 22
5.1.2. Receiving BIBs . . . . . . . . . . . . . . . . . . . 24 5.1.2. Receiving BIBs . . . . . . . . . . . . . . . . . . . 23
5.2. Bundle Fragmentation and Reassembly . . . . . . . . . . . 25 5.2. Bundle Fragmentation and Reassembly . . . . . . . . . . . 24
6. Key Management . . . . . . . . . . . . . . . . . . . . . . . 25 6. Key Management . . . . . . . . . . . . . . . . . . . . . . . 24
7. Security Policy Considerations . . . . . . . . . . . . . . . 25 7. Security Policy Considerations . . . . . . . . . . . . . . . 24
8. Security Considerations . . . . . . . . . . . . . . . . . . . 27 8. Security Considerations . . . . . . . . . . . . . . . . . . . 26
8.1. Attacker Capabilities and Objectives . . . . . . . . . . 27 8.1. Attacker Capabilities and Objectives . . . . . . . . . . 26
8.2. Attacker Behaviors and BPSec Mitigations . . . . . . . . 28 8.2. Attacker Behaviors and BPSec Mitigations . . . . . . . . 27
8.2.1. Eavesdropping Attacks . . . . . . . . . . . . . . . . 28 8.2.1. Eavesdropping Attacks . . . . . . . . . . . . . . . . 27
8.2.2. Modification Attacks . . . . . . . . . . . . . . . . 29 8.2.2. Modification Attacks . . . . . . . . . . . . . . . . 28
8.2.3. Topology Attacks . . . . . . . . . . . . . . . . . . 30 8.2.3. Topology Attacks . . . . . . . . . . . . . . . . . . 29
8.2.4. Message Injection . . . . . . . . . . . . . . . . . . 30 8.2.4. Message Injection . . . . . . . . . . . . . . . . . . 30
9. Security Context Considerations . . . . . . . . . . . . . . . 31 9. Security Context Considerations . . . . . . . . . . . . . . . 30
9.1. Identification and Configuration . . . . . . . . . . . . 31 9.1. Mandating Security Contexts . . . . . . . . . . . . . . . 30
9.2. Authorship . . . . . . . . . . . . . . . . . . . . . . . 31 9.2. Identification and Configuration . . . . . . . . . . . . 31
9.3. Authorship . . . . . . . . . . . . . . . . . . . . . . . 32
10. Defining Other Security Blocks . . . . . . . . . . . . . . . 33 10. Defining Other Security Blocks . . . . . . . . . . . . . . . 33
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
11.1. Bundle Block Types . . . . . . . . . . . . . . . . . . . 34 11.1. Bundle Block Types . . . . . . . . . . . . . . . . . . . 34
11.2. Security Context Identifiers . . . . . . . . . . . . . . 34 11.2. Security Context Identifiers . . . . . . . . . . . . . . 35
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
12.1. Normative References . . . . . . . . . . . . . . . . . . 35 12.1. Normative References . . . . . . . . . . . . . . . . . . 35
12.2. Informative References . . . . . . . . . . . . . . . . . 35 12.2. Informative References . . . . . . . . . . . . . . . . . 36
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 36 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
This document defines security features for the Bundle Protocol (BP) This document defines security features for the Bundle Protocol (BP)
[I-D.ietf-dtn-bpbis] and is intended for use in Delay Tolerant [I-D.ietf-dtn-bpbis] and is intended for use in Delay Tolerant
Networks (DTNs) to provide end-to-end security services. Networks (DTNs) to provide security services between a security
source and a security acceptor. When the security source is the
bundle source and when the security acceptor is the bundle
destination, the security service provides end-to-end protection.
The Bundle Protocol specification [I-D.ietf-dtn-bpbis] defines DTN as The Bundle Protocol specification [I-D.ietf-dtn-bpbis] defines DTN as
referring to "a networking architecture providing communications in referring to "a networking architecture providing communications in
and/or through highly stressed environments" where "BP may be viewed and/or through highly stressed environments" where "BP may be viewed
as sitting at the application layer of some number of constituent as sitting at the application layer of some number of constituent
networks, forming a store-carry-forward overlay network". The term networks, forming a store-carry-forward overlay network". The term
"stressed" environment refers to multiple challenging conditions "stressed" environment refers to multiple challenging conditions
including intermittent connectivity, large and/or variable delays, including intermittent connectivity, large and/or variable delays,
asymmetric data rates, and high bit error rates. asymmetric data rates, and high bit error rates.
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data at rest, preventing unauthorized consumption of critical data at rest, preventing unauthorized consumption of critical
resources such as storage space, and operating without regular resources such as storage space, and operating without regular
contact with a centralized security oracle (such as a certificate contact with a centralized security oracle (such as a certificate
authority). authority).
An end-to-end security service is needed that operates in all of the An end-to-end security service is needed that operates in all of the
environments where the BP operates. environments where the BP operates.
1.1. Supported Security Services 1.1. Supported Security Services
BPSec provides end-to-end integrity and confidentiality services for BPSec provides integrity and confidentiality services for BP bundles,
BP bundles, as defined in this section. as defined in this section.
Integrity services ensure that changes to target data within a bundle Integrity services ensure that changes to target data within a bundle
can be discovered. Data changes may be caused by processing errors, can be discovered. Data changes may be caused by processing errors,
environmental conditions, or intentional manipulation. In the environmental conditions, or intentional manipulation. In the
context of BPSec, integrity services apply to plain-text in the context of BPSec, integrity services apply to plain text in the
bundle. bundle.
Confidentiality services ensure that target data is unintelligible to Confidentiality services ensure that target data is unintelligible to
nodes in the DTN, except for authorized nodes possessing special nodes in the DTN, except for authorized nodes possessing special
information. This generally means producing cipher-text from plain- information. This generally means producing cipher text from plain
text and generating authentication information for that cipher-text. text and generating authentication information for that cipher text.
Confidentiality, in this context, applies to the contents of target Confidentiality, in this context, applies to the contents of target
data and does not extend to hiding the fact that confidentiality data and does not extend to hiding the fact that confidentiality
exists in the bundle. exists in the bundle.
NOTE: Hop-by-hop authentication is NOT a supported security service NOTE: Hop-by-hop authentication is NOT a supported security service
in this specification, for three reasons. in this specification, for two reasons.
1. The term "hop-by-hop" is ambiguous in a BP overlay, as nodes that 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 are adjacent in the overlay may not be adjacent in physical
connectivity. This condition is difficult or impossible to connectivity. This condition is difficult or impossible to
detect and therefore hop-by-hop authentication is difficult or detect and therefore hop-by-hop authentication is difficult or
impossible to enforce. impossible to enforce.
2. Networks in which BPSec may be deployed may have a mixture of 2. Networks in which BPSec may be deployed may have a mixture of
security-aware and not-security-aware nodes. Hop-by-hop security-aware and not-security-aware nodes. Hop-by-hop
authentication cannot be deployed in a network if adjacent nodes authentication cannot be deployed in a network if adjacent nodes
in the network have different security capabilities. in the network have different security capabilities.
3. Hop-by-hop authentication is a special case of data integrity and
can be achieved with the integrity mechanisms defined in this
specification. Therefore, a separate authentication service is
not necessary.
1.2. Specification Scope 1.2. Specification Scope
This document defines the security services provided by the BPSec. This document defines the security services provided by the BPSec.
This includes the data specification for representing these services This includes the data specification for representing these services
as BP extension blocks, and the rules for adding, removing, and as BP extension blocks, and the rules for adding, removing, and
processing these blocks at various points during the bundle's processing these blocks at various points during the bundle's
traversal of the DTN. traversal of the DTN.
BPSec applies only to those nodes that implement it, known as BPSec applies only to those nodes that implement it, known as
"security-aware" nodes. There might be other nodes in the DTN that "security-aware" nodes. There might be other nodes in the DTN that
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This document is best read and understood within the context of the This document is best read and understood within the context of the
following other DTN documents: following other DTN documents:
"Delay-Tolerant Networking Architecture" [RFC4838] defines the "Delay-Tolerant Networking Architecture" [RFC4838] defines the
architecture for DTNs and identifies certain security assumptions architecture for DTNs and identifies certain security assumptions
made by existing Internet protocols that are not valid in a DTN. made by existing Internet protocols that are not valid in a DTN.
The Bundle Protocol [I-D.ietf-dtn-bpbis] defines the format and The Bundle Protocol [I-D.ietf-dtn-bpbis] defines the format and
processing of bundles, defines the extension block format used to processing of bundles, defines the extension block format used to
represent BPSec security blocks, and defines the canonicalization represent BPSec security blocks, and defines the canonical block
algorithms used by this specification. structure used by this specification.
The Concise Binary Object Representation (CBOR) format [RFC7049] The Concise Binary Object Representation (CBOR) format [RFC7049]
defines a data format that allows for small code size, fairly small defines a data format that allows for small code size, fairly small
message size, and extensibility without version negotiation. The message size, and extensibility without version negotiation. The
block-specific data associated with BPSec security blocks are encoded block-specific-data associated with BPSec security blocks are encoded
in this data format. in this data format.
The Bundle Security Protocol [RFC6257] and Streamlined Bundle The Bundle Security Protocol [RFC6257] and Streamlined Bundle
Security Protocol [I-D.birrane-dtn-sbsp] documents introduced the Security Protocol [I-D.birrane-dtn-sbsp] documents introduced the
concepts of using BP extension blocks for security services in a DTN. concepts of using BP extension blocks for security services in a DTN.
The BPSec is a continuation and refinement of these documents. The BPSec is a continuation and refinement of these documents.
1.4. Terminology 1.4. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in BCP
[RFC2119]. 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. .
This section defines terminology either unique to the BPSec or This section defines terminology either unique to the BPSec or
otherwise necessary for understanding the concepts defined in this otherwise necessary for understanding the concepts defined in this
specification. specification.
o Bundle Destination - the node which receives a bundle and delivers o Bundle Destination - the node which receives a bundle and delivers
the payload of the bundle to an application. Also, the Node ID of the payload of the bundle to an application. Also, the Node ID of
the Bundle Protocol Agent (BPA) receiving the bundle. The bundle the Bundle Protocol Agent (BPA) receiving the bundle. The bundle
destination acts as the security acceptor for every security destination acts as the security acceptor for every security
target in every security block in every bundle it receives. target in every security block in every bundle it receives.
o Bundle Source - the node which originates a bundle. Also, the o Bundle Source - the node which originates a bundle. Also, the
Node ID of the BPA originating the bundle. Node ID of the BPA originating the bundle.
o Cipher Suite - a set of one or more algorithms providing integrity o Cipher Suite - a set of one or more algorithms providing integrity
and confidentiality services. Cipher suites may define necessary and/or confidentiality services. Cipher suites may define user
parameters but do not provide values for those parameters. parameters (e.g. secret keys to use) but do not provide values for
those parameters.
o Forwarder - any node that transmits a bundle in the DTN. Also, o Forwarder - any node that transmits a bundle in the DTN. Also,
the Node ID of the BPA that sent the bundle on its most recent the Node ID of the BPA that sent the bundle on its most recent
hop. hop.
o Intermediate Receiver, Waypoint, or Next Hop - any node that o Intermediate Receiver, Waypoint, or Next Hop - any node that
receives a bundle from a Forwarder that is not the Bundle receives a bundle from a Forwarder that is not the Bundle
Destination. Also, the Node ID of the BPA at any such node. Destination. Also, the Node ID of the BPA at any such node.
o Path - the ordered sequence of nodes through which a bundle passes o Path - the ordered sequence of nodes through which a bundle passes
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o Security Context - the set of assumptions, algorithms, o Security Context - the set of assumptions, algorithms,
configurations and policies used to implement security services. configurations and policies used to implement security services.
o Security Operation - the application of a security service to a o Security Operation - the application of a security service to a
security target, notated as OP(security service, security target). security target, notated as OP(security service, security target).
For example, OP(confidentiality, payload). Every security For example, OP(confidentiality, payload). Every security
operation in a bundle MUST be unique, meaning that a 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. service can only be applied to a security target once in a bundle.
A security operation is implemented by a security block. A security operation is implemented by a security block.
o Security Service - the security features supported by this o Security Service - a process that gives some protection to a
specification: either integrity or confidentiality. security target. For example, this specification defines security
services for plain text integrity, plain text confidentiality, and
cipher text integrity.
o Security Source - a bundle node that adds a security block to a o Security Source - a bundle node that adds a security block to a
bundle. Also, the Node ID of that node. bundle. Also, the Node ID of that node.
o Security Target - the block within a bundle that receives a o Security Target - the block within a bundle that receives a
security service as part of a security operation. security service as part of a security operation.
2. Design Decisions 2. Design Decisions
The application of security services in a DTN is a complex endeavor The application of security services in a DTN is a complex endeavor
that must consider physical properties of the network, policies at that must consider physical properties of the network, policies at
each node, and application security requirements. This section each node, application security requirements, and current and future
identifies those desirable properties that guide design decisions for threat environments. This section identifies those desirable
this specification and are necessary for understanding the format and properties that guide design decisions for this specification and are
behavior of the BPSec protocol. necessary for understanding the format and behavior of the BPSec
protocol.
2.1. Block-Level Granularity 2.1. Block-Level Granularity
Security services within this specification must allow different Security services within this specification must allow different
blocks within a bundle to have different security services applied to blocks within a bundle to have different security services applied to
them. them.
Blocks within a bundle represent different types of information. The Blocks within a bundle represent different types of information. The
primary block contains identification and routing information. The primary block contains identification and routing information. The
payload block carries application data. Extension blocks carry a payload block carries application data. Extension blocks carry a
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For example, a payload block might be encrypted to protect its For example, a payload block might be encrypted to protect its
contents and an extension block containing summary information contents and an extension block containing summary information
related to the payload might be integrity signed but unencrypted to related to the payload might be integrity signed but unencrypted to
provide waypoints access to payload-related data without providing provide waypoints access to payload-related data without providing
access to the payload. access to the payload.
2.2. Multiple Security Sources 2.2. Multiple Security Sources
A bundle can have multiple security blocks and these blocks can have A bundle can have multiple security blocks and these blocks can have
different security sources. BPSec implementations MUST NOT assume different security sources. BPSec implementations MUST NOT assume
that all blocks in a bundle have the same security operations and/or that all blocks in a bundle have the same security operations applied
security sources. to them.
The Bundle Protocol allows extension blocks to be added to a bundle The Bundle Protocol allows extension blocks to be added to a bundle
at any time during its existence in the DTN. When a waypoint adds a at any time during its existence in the DTN. When a waypoint adds a
new extension block to a bundle, that extension block MAY have new extension block to a bundle, that extension block MAY have
security services applied to it by that waypoint. Similarly, a security services applied to it by that waypoint. Similarly, a
waypoint MAY add a security service to an existing extension block, waypoint MAY add a security service to an existing extension block,
consistent with its security policy. consistent with its security policy.
When a waypoint adds a security service to the bundle, the waypoint When a waypoint adds a security service to the bundle, the waypoint
is the security source for that service. The security block(s) which is the security source for that service. The security block(s) which
represent that service in the bundle may need to record this security represent that service in the bundle may need to record this security
source as the bundle destination might need this information for source as the bundle destination might need this information for
processing. processing.
For example, a bundle source may choose to apply an integrity service For example, a bundle source may choose to apply an integrity service
to its plain-text payload. Later a waypoint node, representing a to its plain text payload. Later a waypoint node, representing a
gateway to an insecure portion of the DTN, may receive the bundle and gateway to an insecure portion of the DTN, may receive the bundle and
choose to apply a confidentiality service. In this case, the choose to apply a confidentiality service. In this case, the
integrity security source is the bundle source and the integrity security source is the bundle source and the
confidentiality security source is the waypoint node. confidentiality security source is the waypoint node.
2.3. Mixed Security Policy 2.3. Mixed Security Policy
The security policy enforced by nodes in the DTN may differ. The security policy enforced by nodes in the DTN may differ.
Some waypoints might not be security aware and will not be able to Some waypoints might not be security aware and will not be able to
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Some waypoints could understand security blocks but refuse to process Some waypoints could understand security blocks but refuse to process
them unless they are the bundle destination. them unless they are the bundle destination.
2.4. User-Defined Security Contexts 2.4. User-Defined Security Contexts
A security context is the union of security algorithms (cipher A security context is the union of security algorithms (cipher
suites), policies associated with the use of those algorithms, and suites), policies associated with the use of those algorithms, and
configuration values. Different contexts may specify different configuration values. Different contexts may specify different
algorithms, different polices, or different configuration values used algorithms, different polices, or different configuration values used
in the implementation of their security services. BPSec must provide in the implementation of their security services. BPSec provides a
a mechanism for users to define their own security contexts. mechanism to define security contexts. Users may select from
registered security contexts and customize those contexts through
security context parameters.
For example, some users might prefer a SHA2 hash function for For example, some users might prefer a SHA2 hash function for
integrity whereas other users might prefer a SHA3 hash function. The integrity whereas other users might prefer a SHA3 hash function.
security services defined in this specification must provide a Providing either separate security contexts or a single,
mechanism for determining what cipher suite, policy, and parameterized security context allows users flexibility in applying
configuration has been used to populate a security block. the desired cipher suite, policy, and configuration when populating a
security block.
2.5. Deterministic Processing 2.5. Deterministic Processing
Whenever a node determines that it must process more than one Whenever a node determines that it must process more than one
security block in a received bundle (either because the policy at a security block in a received bundle (either because the policy at a
waypoint states that it should process security blocks or because the waypoint states that it should process security blocks or because the
node is the bundle destination) the order in which security blocks node is the bundle destination) the order in which security blocks
are processed must be deterministic. All nodes must impose this same are processed must be deterministic. All nodes must impose this same
deterministic processing order for all security blocks. This deterministic processing order for all security blocks. This
specification provides determinism in the application and evaluation specification provides determinism in the application and evaluation
of security services, even when doing so results in a loss of of security services, even when doing so results in a loss of
flexibility. flexibility.
3. Security Blocks 3. Security Blocks
3.1. Block Definitions 3.1. Block Definitions
This specification defines two types of security block: the Block This specification defines two types of security block: the Block
Integrity Block (BIB) and the Block Confidentiality Block (BCB). Integrity Block (BIB) and the Block Confidentiality Block (BCB).
The BIB is used to ensure the integrity of its plain-text security The BIB is used to ensure the integrity of its plain text security
target(s). The integrity information in the BIB MAY be verified target(s). The integrity information in the BIB MAY be verified
by any node along the bundle path from the BIB security source to by any node along the bundle path from the BIB security source to
the bundle destination. Security-aware waypoints add or remove the bundle destination. Security-aware waypoints add or remove
BIBs from bundles in accordance with their security policy. BIBs BIBs from bundles in accordance with their security policy. BIBs
are never used to sign the cipher-text provided by a BCB. are never used for integrity protection of the cipher text
provided by a BCB.
The BCB indicates that the security target(s) have been encrypted The BCB indicates that the security target(s) have been encrypted
at the BCB security source in order to protect their content while at the BCB security source in order to protect their content while
in transit. The BCB is decrypted by security-aware nodes in the in transit. The BCB is decrypted by security-aware nodes in the
network, up to and including the bundle destination, as a matter network, up to and including the bundle destination, as a matter
of security policy. BCBs additionally provide authentication of security policy. BCBs additionally provide integrity
mechanisms for the cipher-text they generate. protection mechanisms for the cipher text they generate.
3.2. Uniqueness 3.2. Uniqueness
Security operations in a bundle MUST be unique; the same security Security operations in a bundle MUST be unique; the same security
service MUST NOT be applied to a security target more than once in a service MUST NOT be applied to a security target more than once in a
bundle. Since a security operation is represented as a security bundle. Since a security operation is represented as a security
block, this limits what security blocks may be added to a bundle: if block, this limits what security blocks may be added to a bundle: if
adding a security block to a bundle would cause some other security adding a security block to a bundle would cause some other security
block to no longer represent a unique security operation then the new block to no longer represent a unique security operation then the new
block MUST NOT be added. It is important to note that any cipher- block MUST NOT be added.
text integrity mechanism supplied by the BCB is considered part of
the confidentiality service and, therefore, unique from the plain- A security operation may be removed from a bundle as part of
text integrity service provided by the BIB. processing a security block and, once removed, the same security
operation may be re-applied by adding a new security block into the
bundle. In this case, conflicting security blocks never co-exist in
the bundle at the same time.
It is important to note that any cipher text integrity mechanism
supplied by the BCB is considered part of the confidentiality service
and, therefore, unique from the plain text integrity service provided
by the BIB.
If multiple security blocks representing the same security operation If multiple security blocks representing the same security operation
were allowed in a bundle at the same time, there would exist were allowed in a bundle at the same time, there would exist
ambiguity regarding block processing order and the property of ambiguity regarding block processing order and the property of
deterministic processing of blocks would be lost. deterministic processing of blocks would be lost.
Using the notation OP(service, target), several examples illustrate Using the notation OP(service, target), several examples illustrate
this uniqueness requirement. this uniqueness requirement.
o Signing the payload twice: The two operations OP(integrity, o Signing the payload twice: The two operations OP(integrity,
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OP(integrity,extension_block_2) are also not redundant and may OP(integrity,extension_block_2) are also not redundant and may
both be present in the bundle at the same time. both be present in the bundle at the same time.
o Different Services on same block: The two operations OP(integrity, o Different Services on same block: The two operations OP(integrity,
payload) and OP(confidentiality, payload) are not inherently payload) and OP(confidentiality, payload) are not inherently
redundant and may both be present in the bundle at the same time, redundant and may both be present in the bundle at the same time,
pursuant to other processing rules in this specification. pursuant to other processing rules in this specification.
3.3. Target Multiplicity 3.3. Target Multiplicity
Under special circumstances, a single security block MAY represent A single security block MAY represent multiple security operations as
multiple security operations as a way of reducing the overall number a way of reducing the overall number of security blocks present in a
of security blocks present in a bundle. In these circumstances, bundle. In these circumstances, reducing the number of security
reducing the number of security blocks in the bundle reduces the blocks in the bundle reduces the amount of redundant information in
amount of redundant information in the bundle. the bundle.
A set of security operations can be represented by a single security A set of security operations can be represented by a single security
block when all of the following conditions are true. block when all of the following conditions are true.
o The security operations apply the same security service. For o The security operations apply the same security service. For
example, they are all integrity operations or all confidentiality example, they are all integrity operations or all confidentiality
operations. operations.
o The security context parameters for the security operations are o The security context parameters for the security operations are
identical. identical.
o The security source for the security operations is the same. o The security source for the security operations is the same,
Meaning the set of operations are being added by the same node. meaning the set of operations are being added by the same node.
o No security operations have the same security target, as that o No security operations have the same security target, as that
would violate the need for security operations to be unique. would violate the need for security operations to be unique.
o None of the security operations conflict with security operations o None of the security operations conflict with security operations
already present in the bundle. already present in the bundle.
When representing multiple security operations in a single security When representing multiple security operations in a single security
block, the information that is common across all operations is block, the information that is common across all operations is
represented once in the security block, and the information which is represented once in the security block, and the information which is
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Number" field suitable for this purpose. Therefore, a security Number" field suitable for this purpose. Therefore, a security
target in a security block MUST be represented as the Block Number of target in a security block MUST be represented as the Block Number of
the target block. the target block.
3.5. Block Representation 3.5. Block Representation
Each security block uses the Canonical Bundle Block Format as defined Each security block uses the Canonical Bundle Block Format as defined
in [I-D.ietf-dtn-bpbis]. That is, each security block is comprised in [I-D.ietf-dtn-bpbis]. That is, each security block is comprised
of the following elements: of the following elements:
o Block Type Code o block type code
o Block Number o block number
o Block Processing Control Flags o block processing control flags
o CRC Type and CRC Field (if present) o CRC type
o Block Data Length o block-type-specific-data
o Block Type Specific Data Fields o CRC field (if present)
Security-specific information for a security block is captured in the Security-specific information for a security block is captured in the
"Block Type Specific Data Fields". block-type-specific-data field.
3.6. Abstract Security Block 3.6. Abstract Security Block
The structure of the security-specific portions of a security block The structure of the security-specific portions of a security block
is identical for both the BIB and BCB Block Types. Therefore, this is identical for both the BIB and BCB Block Types. Therefore, this
section defines an Abstract Security Block (ASB) data structure and section defines an Abstract Security Block (ASB) data structure and
discusses the definition, processing, and other constraints for using discusses the definition, processing, and other constraints for using
this structure. An ASB is never directly instantiated within a this structure. An ASB is never directly instantiated within a
bundle, it is only a mechanism for discussing the common aspects of bundle, it is only a mechanism for discussing the common aspects of
BIB and BCB security blocks. BIB and BCB security blocks.
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target within this CBOR array SHALL be represented by a CBOR target within this CBOR array SHALL be represented by a CBOR
unsigned integer. This array MUST have at least 1 entry and unsigned integer. This array MUST have at least 1 entry and
each entry MUST represent the Block Number of a block that each entry MUST represent the Block Number of a block that
exists in the bundle. There MUST NOT be duplicate entries in exists in the bundle. There MUST NOT be duplicate entries in
this array. this array.
Security Context Id: Security Context Id:
This field identifies the security context used to implement This field identifies the security context used to implement
the security service represented by this block and applied to the security service represented by this block and applied to
each security target. This field SHALL be represented by a each security target. This field SHALL be represented by a
CBOR unsigned integer. CBOR unsigned integer. The values for this Id should come from
the registry defined in Section 11.2
Security Context Flags: Security Context Flags:
This field identifies which optional fields are present in the This field identifies which optional fields are present in the
security block. This field SHALL be represented as a CBOR security block. This field SHALL be represented as a CBOR
unsigned integer whose contents shall be interpreted as a bit unsigned integer whose contents shall be interpreted as a bit
field. Each bit in this bit field indicates the presence (bit field. Each bit in this bit field indicates the presence (bit
set to 1) or absence (bit set to 0) of optional data in the set to 1) or absence (bit set to 0) of optional data in the
security block. The association of bits to security block data security block. The association of bits to security block data
is defined as follows. is defined as follows.
Bit 1 (the least-significant bit, 0x01): Security Context Bit 0 (the least-significant bit, 0x01): Security Context
Parameters Present Flag. Parameters Present Flag.
Bit 2 (0x02): Security Source Present Flag. Bit 1 (0x02): Security Source Present Flag.
Bit >2 Reserved Bit >1 Reserved
Implementations MUST set reserved bits to 0 when writing this Implementations MUST set reserved bits to 0 when writing this
field and MUST ignore the values of reserved bits when reading field and MUST ignore the values of reserved bits when reading
this field. For unreserved bits, a value of 1 indicates that this field. For unreserved bits, a value of 1 indicates that
the associated security block field MUST be included in the the associated security block field MUST be included in the
security block. A value of 0 indicates that the associated security block. A value of 0 indicates that the associated
security block field MUST NOT be in the security block. security block field MUST NOT be in the security block.
Security Source (Optional): Security Source (Optional):
This field identifies the Endpoint that inserted the security This field identifies the Endpoint that inserted the security
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in Section 3.10. in Section 3.10.
* Parameter Value. This field captures the value associated * Parameter Value. This field captures the value associated
with this parameter. This field SHALL be represented by the with this parameter. This field SHALL be represented by the
applicable CBOR representation of the parameter, in applicable CBOR representation of the parameter, in
accordance with Section 3.10. accordance with Section 3.10.
The logical layout of the parameters array is illustrated in The logical layout of the parameters array is illustrated in
Figure 1. Figure 1.
+----------------+----------------+ +----------------+
| Parameter 1 | Parameter 2 | ... | Parameter N |
+------+---------+------+---------+ +------+---------+
| Id | Value | Id | Value | | Id | Value |
+------+---------+------+---------+ +------+---------+
Figure 1: Security Context Parameters Figure 1: Security Context Parameters
Security Results: Security Results:
This field captures the results of applying a security service This field captures the results of applying a security service
to the security targets of the security block. This field to the security targets of the security block. This field
SHALL be represented as a CBOR array of target results. Each SHALL be represented as a CBOR array of target results. Each
entry in this array represents the set of security results for entry in this array represents the set of security results for
a specific security target. The target results MUST be ordered a specific security target. The target results MUST be ordered
identically to the Security Targets field of the security identically to the Security Targets field of the security
block. This means that the first set of target results in this block. This means that the first set of target results in this
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* Result Value. This field captures the value associated with * Result Value. This field captures the value associated with
the result. This field SHALL be represented by the the result. This field SHALL be represented by the
applicable CBOR representation of the result value, in applicable CBOR representation of the result value, in
accordance with Section 3.10. accordance with Section 3.10.
The logical layout of the security results array is illustrated The logical layout of the security results array is illustrated
in Figure 2. In this figure there are N security targets for in Figure 2. In this figure there are N security targets for
this security block. The first security target contains M this security block. The first security target contains M
results and the Nth security target contains K results. results and the Nth security target contains K results.
+------------------------------+ +------------------------------+
| Target 1 | | Target N |
+------------+----+------------+ +------------------------------+
| Result 1 | | Result M | ... | Result 1 | | Result K |
+----+-------+ .. +----+-------+ +----+-------+ .. +----+-------+
| Id | Value | | Id | Value | | Id | Value | | Id | Value |
+----+-------+ +----+-------+ +----+-------+ +----+-------+
Figure 2: Security Results Figure 2: Security Results
3.7. Block Integrity Block 3.7. Block Integrity Block
A BIB is a bundle extension block with the following characteristics. A BIB is a bundle extension block with the following characteristics.
o The Block Type Code value is as specified in Section 11.1. The Block Type Code value is as specified in Section 11.1.
o The Block Type Specific Data Fields follow the structure of the The block-type-specific-data field follows the structure of the
ASB. ASB.
o A security target listed in the Security Targets field MUST NOT A security target listed in the Security Targets field MUST NOT
reference a security block defined in this specification (e.g., a reference a security block defined in this specification (e.g., a
BIB or a BCB). BIB or a BCB).
o The Security Context Id MUST utilize an end-to-end authentication The Security Context MUST utilize an authentication mechanism or
cipher or an end-to-end error detection cipher. an error detection mechanism.
o The EID of the security source MAY be present. If this field is The EID of the security source MAY be present. If this field is
not present, then the security source of the block SHOULD be not present, then the security source of the block SHOULD be
inferred according to security policy and MAY default to the inferred according to security policy and MAY default to the
bundle source. The security source MAY be specified as part of bundle source. The security source MAY be specified as part of
security context information described in Section 3.10. security context parameters described in Section 3.10.
Notes: Notes:
o It is RECOMMENDED that designers carefully consider the effect of o It is recommended that designers carefully consider the effect of
setting flags that either discard the block or delete the bundle setting flags that either discard the block or delete the bundle
in the event that this block cannot be processed. in the event that this block cannot be processed.
o Since OP(integrity, target) is allowed only once in a bundle per o Since OP(integrity, target) is allowed only once in a bundle per
target, it is RECOMMENDED that users wishing to support multiple target, it is RECOMMENDED that users wishing to support multiple
integrity signatures for the same target define a multi-signature integrity signatures for the same target define a multi-signature
security context. security context.
o For some security contexts, (e.g., those using asymmetric keying o Security information MAY be checked at any hop on the way to the
to produce signatures or those using symmetric keying with a group bundle destination that has access to the required keying
key), the security information MAY be checked at any hop on the information, in accordance with Section 3.9.
way to the bundle destination that has access to the required
keying information, in accordance with Section 3.9.
3.8. Block Confidentiality Block 3.8. Block Confidentiality Block
A BCB is a bundle extension block with the following characteristics. A BCB is a bundle extension block with the following characteristics.
The Block Type Code value is as specified in Section 11.1. The Block Type Code value is as specified in Section 11.1.
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, except that this block MUST values are required by local policy with the following exceptions.
have the "replicate in every fragment" flag set if the target of BCB blocks MUST have the "block must be replicated in every
the BCB is the Payload Block. Having that BCB in each fragment fragment" flag set if one of the targets is the payload block.
indicates to a receiving node that the payload portion of each Having that BCB in each fragment indicates to a receiving node
fragment represents cipher-text. that the payload portion of each fragment represents cipher text.
BCB blocks MUST NOT have the "block must be removed from bundle if
it can't be processed" flag set. Removing a BCB from a bundle
without decrypting its security targets removes information from
the bundle necessary for their later decryption.
The Block Type Specific Data Fields follow the structure of the The block-type-specific-data fields follow the structure of the
ASB. ASB.
A security target listed in the Security Targets field can A security target listed in the Security Targets field can
reference the payload block, a non-security extension block, or a reference the payload block, a non-security extension block, or a
BIB. A BCB MUST NOT include another BCB as a security target. A BIB. A BCB MUST NOT include another BCB as a security target. A
BCB MUST NOT target the primary block. BCB MUST NOT target the primary block.
The Security Context Id MUST utilize a confidentiality cipher that The Security Context MUST utilize a confidentiality cipher that
provides authenticated encryption with associated data (AEAD). provides authenticated encryption with associated data (AEAD).
Additional information created by a cipher suite (such as Additional information created by a cipher suite (such as an
additional authenticated data) can be placed either in a security authentication tag) can be placed either in a security result
result field or in the generated cipher-text. The determination field or in the generated cipher text. The determination of where
of where to place these data is a function of the cipher suite and to place this information is a function of the cipher suite and
security context used. security context used.
The EID of the security source MAY be present. If this field is The EID of the security source MAY be present. If this field is
not present, then the security source of the block SHOULD be not present, then the security source of the block SHOULD be
inferred according to security policy and MAY default to the inferred according to security policy and MAY default to the
bundle source. The security source MAY be specified as part of bundle source. The security source MAY be specified as part of
security context information described in Section 3.10. security context parameters described in Section 3.10.
The BCB modifies the contents of its security target(s). When a BCB The BCB modifies the contents of its security target(s). When a BCB
is applied, the security target body data are encrypted "in-place". is applied, the security target body data are encrypted "in-place".
Following encryption, the security target Block Type Specific Data Following encryption, the security target block-type-specific-data
field contains cipher-text, not plain-text. Other block fields field contains cipher text, not plain text.
remain unmodified, with the exception of the Block Data Length field,
which MUST be updated to reflect the new length of the Block Type
Specific Data field.
Notes: Notes:
o It is RECOMMENDED that designers carefully consider the effect of o It is RECOMMENDED that designers carefully consider the effect of
setting flags that either discard the block or delete the bundle setting flags that delete the bundle in the event that this block
in the event that this block cannot be processed. cannot be processed.
o The BCB block processing control flags can be set independently o The BCB block processing control flags can be set independently
from the processing control flags of the security target(s). The from the processing control flags of the security target(s). The
setting of such flags SHOULD be an implementation/policy decision setting of such flags should be an implementation/policy decision
for the encrypting node. for the encrypting node.
3.9. Block Interactions 3.9. Block Interactions
The security block types defined in this specification are designed The security block types defined in this specification are designed
to be as independent as possible. However, there are some cases to be as independent as possible. However, there are some cases
where security blocks may share a security target creating processing where security blocks may share a security target creating processing
dependencies. dependencies.
If a security target of a BCB is also a security target of a BIB, an If a security target of a BCB is also a security target of a BIB, an
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targets of a BIB then that BIB MUST be altered in the following targets of a BIB then that BIB MUST be altered in the following
way. Any security results in the BIB associated with the BCB way. Any security results in the BIB associated with the BCB
security targets MUST be removed from the BIB and placed in a new security targets MUST be removed from the BIB and placed in a new
BIB. This newly created BIB MUST then be encrypted. The BIB. This newly created BIB MUST then be encrypted. The
encryption of the new BIB can be accomplished by either adding a encryption of the new BIB can be accomplished by either adding a
new BCB that targets the new BIB, or by adding the new BIB to the new BCB that targets the new BIB, or by adding the new BIB to the
list of security targets for the BCB. Deciding which way to list of security targets for the BCB. Deciding which way to
represent this situation is a matter of security policy. represent this situation is a matter of security policy.
o A BIB MUST NOT be added for a security target that is already the o A BIB MUST NOT be added for a security target that is already the
security target of a BCB. In this instance, the BCB is already security target of a BCB as this would cause ambiguity in block
providing authentication and integrity of the security target and
the BIB would be redundant, insecure, and cause ambiguity in block
processing order. processing order.
o A BIB integrity value MUST NOT be evaluated if the BIB is the o A BIB integrity value MUST NOT be checked if the BIB is the
security target of an existing BCB. In this case, the BIB data is security target of an existing BCB. In this case, the BIB data is
encrypted. encrypted.
o A BIB integrity value MUST NOT be evaluated if the security target o A BIB integrity value MUST NOT be checked if the security target
of the BIB is also the security target of a BCB. In such a case, associated with that value is also the security target of a BCB.
the security target data contains cipher-text as it has been In such a case, the security target data contains cipher text as
encrypted. it has been encrypted.
o As mentioned in Section 3.7, a BIB MUST NOT have a BCB as its o As mentioned in Section 3.7, a BIB MUST NOT have a BCB as its
security target. security target.
These restrictions on block interactions impose a necessary ordering These restrictions on block interactions impose a necessary ordering
when applying security operations within a bundle. Specifically, for when applying security operations within a bundle. Specifically, for
a given security target, BIBs MUST be added before BCBs. This a given security target, BIBs MUST be added before BCBs. This
ordering MUST be preserved in cases where the current BPA is adding 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 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 waypoint adding new security blocks to a bundle that already contains
security blocks. security blocks.
Since any cipher suite used with a BCB MUST be an AEAD cipher suite, In cases where a security source wishes to calculate both a plain
it is inefficient and insecure for a single security source to add text integrity mechanism and encrypt a security target, a BCB with a
both a BIB and a BCB for the same security target. In cases where a security context that generates such signatures as additional
security source wishes to calculate both a plain-text integrity security results MUST be used instead of adding both a BIB and then a
mechanism and encrypt a security target, a BCB with a security BCB for the security target at the security source.
context that generates such signatures as additional security results
MUST be used instead.
3.10. Parameter and Result Identification 3.10. Parameter and Result Identification
Each security context MUST define its own context parameters and Each security context MUST define its own context parameters and
results. Each defined parameter and result is represented as the results. Each defined parameter and result is represented as the
tuple of an identifier and a value. Identifiers are always tuple of an identifier and a value. Identifiers are always
represented as a CBOR unsigned integer. The CBOR encoding of values represented as a CBOR unsigned integer. The CBOR encoding of values
is as defined by the security context specification. is as defined by the security context specification.
Identifiers MUST be unique for a given security context but do not Identifiers MUST be unique for a given security context but do not
need to be unique amongst all security contexts. need to be unique amongst all security contexts.
An example of a security context can be found at
[I-D.ietf-dtn-bpsec-interop-sc].
3.11. BSP Block Examples 3.11. BSP Block Examples
This section provides two examples of BPSec blocks applied to a This section provides two examples of BPSec blocks applied to a
bundle. In the first example, a single node adds several security bundle. In the first example, a single node adds several security
operations to a bundle. In the second example, a waypoint node operations to a bundle. In the second example, a waypoint node
received the bundle created in the first example and adds additional received the bundle created in the first example and adds additional
security operations. In both examples, the first column represents security operations. In both examples, the first column represents
blocks within a bundle and the second column represents the Block blocks within a bundle and the second column represents the Block
Number for the block, using the terminology B1...Bn for the purpose Number for the block, using the terminology B1...Bn for the purpose
of illustration. of illustration.
3.11.1. Example 1: Constructing a Bundle with Security 3.11.1. Example 1: Constructing a Bundle with Security
In this example a bundle has four non-security-related blocks: the In this example a bundle has four non-security-related blocks: the
primary block (B1), two extension blocks (B4,B5), and a payload block primary block (B1), two extension blocks (B4,B5), and a payload block
(B6). The bundle source wishes to provide an integrity signature of (B6). The bundle source wishes to provide an integrity signature of
the plain-text associated with the primary block, the second the plain text associated with the primary block, the second
extension block, and the payload. The bundle source also wishes to extension block, and the payload. The bundle source also wishes to
provide confidentiality for the first extension block. The resultant provide confidentiality for the first extension block. The resultant
bundle is illustrated in Figure 3 and the security actions are bundle is illustrated in Figure 3 and the security actions are
described below. described below.
Block in Bundle ID
+======================================+====+
| Primary Block | B1 |
+--------------------------------------+----+
| BIB | B2 |
| OP(integrity, targets=B1, B5, B6) | |
+--------------------------------------+----+
| BCB | B3 |
| OP(confidentiality, target=B4) | |
+--------------------------------------+----+
| Extension Block (encrypted) | B4 |
+--------------------------------------+----+
| Extension Block | B5 |
+--------------------------------------+----+
| Payload Block | B6 |
+--------------------------------------+----+
Figure 3: Security at Bundle Creation Figure 3: Security at Bundle Creation
The following security actions were applied to this bundle at its The following security actions were applied to this bundle at its
time of creation. time of creation.
o An integrity signature applied to the canonicalized primary block o An integrity signature applied to the canonical form of the
(B1), the second extension block (B5) and the payload block (B6). primary block (B1), the canonical form of the block-type-specific-
This is accomplished by a single BIB (B2) with multiple targets. data field of the second extension block (B5) and the canonical
A single BIB is used in this case because all three targets share form of the payload block (B6). This is accomplished by a single
a security source, security context, and security context BIB (B2) with multiple targets. A single BIB is used in this case
parameters. Had this not been the case, multiple BIBs could have because all three targets share a security source, security
been added instead. context, and security context parameters. Had this not been the
case, multiple BIBs could have been added instead.
o Confidentiality for the first extension block (B4). This is o Confidentiality for the first extension block (B4). This is
accomplished by a BCB (B3). Once applied, the contents of accomplished by a BCB (B3). Once applied, the block-type-
extension block B4 are encrypted. The BCB MUST hold an specific-data field of extension block B4 is encrypted. The BCB
authentication signature for the cipher-text either in the cipher- MUST hold an authentication tag for the cipher text either in the
text that now populates the first extension block or as a security cipher text that now populates the first extension block or as a
result in the BCB itself, depending on which security context is security result in the BCB itself, depending on which security
used to form the BCB. A plain-text integrity signature may also context is used to form the BCB. A plain text integrity signature
exist as a security result in the BCB if one is provided by the may also exist as a security result in the BCB if one is provided
selected confidentiality security context. by the selected confidentiality security context.
3.11.2. Example 2: Adding More Security At A New Node 3.11.2. Example 2: Adding More Security At A New Node
Consider that the bundle as it is illustrated in Figure 3 is now Consider that the bundle as it is illustrated in Figure 3 is now
received by a waypoint node that wishes to encrypt the second received by a waypoint node that wishes to encrypt the second
extension block and the bundle payload. The waypoint security policy extension block and the bundle payload. The waypoint security policy
is to allow existing BIBs for these blocks to persist, as they may be is to allow existing BIBs for these blocks to persist, as they may be
required as part of the security policy at the bundle destination. required as part of the security policy at the bundle destination.
The resultant bundle is illustrated in Figure 4 and the security The resultant bundle is illustrated in Figure 4 and the security
actions are described below. Note that block IDs provided here are actions are described below. Note that block IDs provided here are
ordered solely for the purpose of this example and not meant to ordered solely for the purpose of this example and not meant to
impose an ordering for block creation. The ordering of blocks added impose an ordering for block creation. The ordering of blocks added
to a bundle MUST always be in compliance with [I-D.ietf-dtn-bpbis]. to a bundle MUST always be in compliance with [I-D.ietf-dtn-bpbis].
Block in Bundle ID
+======================================+====+
| Primary Block | B1 |
+--------------------------------------+----+
| BIB | B2 |
| OP(integrity, targets=B1) | |
+--------------------------------------+----+
| BIB (encrypted) | B7 |
| OP(integrity, targets=B5, B6) | |
+--------------------------------------+----+
| BCB | B8 |
| OP(confidentiality, target=B5,B6,B7) | |
+--------------------------------------+----+
| BCB | B3 |
| OP(confidentiality, target=B4) | |
+--------------------------------------+----+
| Extension Block (encrypted) | B4 |
+--------------------------------------+----+
| Extension Block (encrypted) | B5 |
+--------------------------------------+----+
| Payload Block (encrypted) | B6 |
+--------------------------------------+----+
Figure 4: Security At Bundle Forwarding Figure 4: Security At Bundle Forwarding
The following security actions were applied to this bundle prior to The following security actions were applied to this bundle prior to
its forwarding from the waypoint node. its forwarding from the waypoint node.
o Since the waypoint node wishes to encrypt blocks B5 and B6, it o Since the waypoint node wishes to encrypt the block-type-specific-
MUST also encrypt the BIBs providing plain-text integrity over data field of blocks B5 and B6, it MUST also encrypt the block-
those blocks. However, BIB B2 could not be encrypted in its type-specific-data field of the BIBs providing plain text
entirety because it also held a signature for the primary block integrity over those blocks. However, BIB B2 could not be
(B1). Therefore, a new BIB (B7) is created and security results encrypted in its entirety because it also held a signature for the
associated with B5 and B6 are moved out of BIB B2 and into BIB B7. primary block (B1). Therefore, a new BIB (B7) is created and
security results associated with B5 and B6 are moved out of BIB B2
and into BIB B7.
o Now that there is no longer confusion of which plain-text o Now that there is no longer confusion of which plain text
integrity signatures must be encrypted, a BCB is added to the integrity signatures must be encrypted, a BCB is added to the
bundle with the security targets being the second extension block bundle with the security targets being the second extension block
(B5) and the payload (B6) as well as the newly created BIB holding (B5) and the payload (B6) as well as the newly created BIB holding
their plain-text integrity signatures (B7). A single new BCB is their plain text integrity signatures (B7). A single new BCB is
used in this case because all three targets share a security used in this case because all three targets share a security
source, security context, and security context parameters. Had source, security context, and security context parameters. Had
this not been the case, multiple BCBs could have been added this not been the case, multiple BCBs could have been added
instead. instead.
4. Canonical Forms 4. Canonical Forms
Security services require consistency and determinism in how Security services require consistency and determinism in how
information is presented to cipher suites at the security source and information is presented to cipher suites at the security source and
at a receiving node. For example, integrity services require that at a receiving node. For example, integrity services require that
the same target information (e.g., the same bits in the same order) the same target information (e.g., the same bits in the same order)
is provided to the cipher suite when generating an original signature is provided to the cipher suite when generating an original signature
and when generating a comparison signature. Canonicalization and when validating a signature. Canonicalization algorithms are
algorithms are used to construct a stable, end-to-end bit used to construct a stable, end-to-end bit representation of a target
representation of a target block. block.
Canonical forms are not transmitted, they are used to generate input Canonical forms are used to generate input to a security context for
to a cipher suite for security processing at a security-aware node. security processing at a security-aware node.
The canonicalization of the primary block is as specified in BPSec operates on data fields within bundle blocks (e.g., the block-
type-specific-data field). In their canonical form, these fields
MUST include their own CBOR encoding and MUST NOT include any other
encapsulating CBOR encoding. For example, the canonical form of the
block-type-specific-data field is a CBOR byte string existing within
the CBOR array containing the fields of the extension block. The
entire CBOR byte string is considered the canonical block-type-
specific-data field. The CBOR array framing is not considered part
of the field.
The canonical form of the primary block is specified in
[I-D.ietf-dtn-bpbis]. [I-D.ietf-dtn-bpbis].
All non-primary blocks share the same block structure and are All non-primary blocks share the same block structure and are
canonicalized as specified in [I-D.ietf-dtn-bpbis] with the following canonicalized as specified in [I-D.ietf-dtn-bpbis] with the following
exceptions. exceptions.
o If the service being applied is a confidentiality service, then o If the service being applied is a confidentiality service, then
the Block Type Code, Block Number, Block Processing Control Flags, the block type code, block number, block processing control flags,
CRC Type and CRC Field (if present), and Block Data Length fields CRC type and CRC field (if present), and the length indication of
MUST NOT be included in the canonicalization. Confidentiality the block-type-specific-data field MUST NOT be included in a
services are used solely to convert the Block Type Specific Data canonical form. Confidentiality services are used solely to
Fields from plain-text to cipher-text. convert block data in the block-type-specific-data field from
plain text to cipher text.
o Reserved flags MUST NOT be included in any canonicalization as it
is not known if those flags will change in transit.
These canonicalization algorithms assume that Endpoint IDs do not o Reserved flags in the block processing control flags field MUST
change from the time at which a security source adds a security block NOT be included in a canonical form as it is not known if those
to a bundle and the time at which a node processes that security flags will change in transit.
block.
Cipher suites and security contexts MAY define their own Cipher suites and security contexts MAY define their own
canonicalization algorithms and require the use of those algorithms canonicalization algorithms and require the use of those algorithms
over the ones provided in this specification. In the event of over the ones provided in this specification. In the event of
conflicting canonicalization algorithms, those algorithms take conflicting canonicalization algorithms, those algorithms take
precedence over this specification. precedence over this specification.
5. Security Processing 5. Security Processing
This section describes the security aspects of bundle processing. This section describes the security aspects of bundle processing.
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be processed according to the security policy. A bundle status be processed according to the security policy. A bundle status
report indicating the failure MAY be generated. When all security report indicating the failure MAY be generated. When all security
operations for a BCB have been removed from the BCB, the BCB MUST be operations for a BCB have been removed from the BCB, the BCB MUST be
removed from the bundle. removed from the bundle.
If the receiving node is the destination of the bundle, the node MUST 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 decrypt any BCBs remaining in the bundle. If the receiving node is
not the destination of the bundle, the node MUST process the BCB if not the destination of the bundle, the node MUST process the BCB if
directed to do so as a matter of security policy. directed to do so as a matter of security policy.
If the security policy of a security-aware node specifies that a If the security policy of a security-aware node specifies that a node
bundle should have applied confidentiality to a specific security should have applied confidentiality to a specific security target and
target and no such BCB is present in the bundle, then the node MUST no such BCB is present in the bundle, then the node MUST process this
process this security target in accordance with the security policy. security target in accordance with the security policy. It is
This may involve removing the security target from the bundle. If recommended that the node remove the security target from the bundle.
the removed security target is the payload block, the bundle MUST be If the removed security target is the payload block, the bundle MUST
discarded. be discarded.
If an encrypted payload block cannot be decrypted (i.e., the cipher- If an encrypted payload block cannot be decrypted (i.e., the cipher
text cannot be authenticated), then the bundle MUST be discarded and text cannot be authenticated), then the bundle MUST be discarded and
processed no further. If an encrypted security target other than the processed no further. If an encrypted security target other than the
payload block cannot be decrypted then the associated security target payload block cannot be decrypted then the associated security target
and all security blocks associated with that target MUST be discarded and all security blocks associated with that target MUST be discarded
and processed no further. In both cases, requested status reports and processed no further. In both cases, requested status reports
(see [I-D.ietf-dtn-bpbis]) MAY be generated to reflect bundle or (see [I-D.ietf-dtn-bpbis]) MAY be generated to reflect bundle or
block deletion. block deletion.
When a BCB is decrypted, the recovered plain-text MUST replace the When a BCB is decrypted, the recovered plain text for each security
cipher-text in the security target Block Type Specific Data Fields. target MUST replace the cipher text in each of the security targets'
If the Block Data Length field was modified at the time of encryption block-type-specific-data fields. If the plain text is of different
it MUST be updated to reflect the decrypted block length. size than the cipher text, the CBOR byte string framing of this field
must be updated to ensure this field remains a valid CBOR byte
string. The length of the recovered plain text is known by the
decrypting security context.
If a BCB contains multiple security operations, each operation If a BCB contains multiple security operations, each operation
processed by the node MUST be be treated as if the security operation processed by the node MUST be treated as if the security operation
has been represented by a single BCB with a single security operation has been represented by a single BCB with a single security operation
for the purposes of report generation and policy processing. for the purposes of report generation and policy processing.
5.1.2. Receiving BIBs 5.1.2. Receiving BIBs
If a received bundle contains a BIB, the receiving node MUST If a received bundle contains a BIB, the receiving node MUST
determine whether it is the security acceptor for any of the security determine whether it is the security acceptor for any of the security
operations in the BIB. If so, the node MUST process those operations operations in the BIB. If so, the node MUST process those operations
and remove any operation-specific information from the BIB prior to and remove any operation-specific information from the BIB prior to
delivering data to an application at the node or forwarding the delivering data to an application at the node or forwarding the
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removed from the bundle. removed from the bundle.
A BIB MUST NOT be processed if the security target of the BIB is also 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 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 operations mandated by this specification, when both a BIB and a BCB
share a security target, it means that the security target must have share a security target, it means that the security target must have
been encrypted after it was integrity signed and, therefore, the BIB been encrypted after it was integrity signed and, therefore, the BIB
cannot be verified until the security target has been decrypted by cannot be verified until the security target has been decrypted by
processing the BCB. processing the BCB.
If the security policy of a security-aware node specifies that a If the security policy of a security-aware node specifies that a node
bundle should have applied integrity to a specific security target should have applied integrity to a specific security target and no
and no such BIB is present in the bundle, then the node MUST process such BIB is present in the bundle, then the node MUST process this
this security target in accordance with the security policy. This security target in accordance with the security policy. It is
may involve removing the security target from the bundle. If the RECOMMENDED that the node remove the security target from the bundle
removed security target is the payload or primary block, the bundle if the security target is not the payload or primary block. If the
MAY be discarded. This action can occur at any node that has the security target is the payload or primary block, the bundle MAY be
ability to verify an integrity signature, not just the bundle discarded. This action can occur at any node that has the ability to
destination. verify an integrity signature, not just the bundle destination.
If a receiving node is not the security acceptor of a security If a receiving node is not the security acceptor of a security
operation in a BIB it MAY attempt to verify the security operation operation in a BIB it MAY attempt to verify the security operation
anyway to prevent forwarding corrupt data. If the verification anyway to prevent forwarding corrupt data. If the verification
fails, the node SHALL process the security target in accordance to fails, the node SHALL process the security target in accordance to
local security policy. It is RECOMMENDED that if a payload integrity 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 check fails at a waypoint that it is processed in the same way as if
the check fails at the bundle destination. If the check passes, the the check fails at the bundle destination. If the check passes, the
node MUST NOT remove the security operation from the BIB prior to node MUST NOT remove the security operation from the BIB prior to
forwarding. forwarding.
If a BIB contains multiple security operations, each operation If a BIB contains multiple security operations, each operation
processed by the node MUST be be treated as if the security operation processed by the node MUST be treated as if the security operation
has been represented by a single BIB with a single security operation has been represented by a single BIB with a single security operation
for the purposes of report generation and policy processing. for the purposes of report generation and policy processing.
5.2. Bundle Fragmentation and Reassembly 5.2. Bundle Fragmentation and Reassembly
If it is necessary for a node to fragment a bundle payload, and If it is necessary for a node to fragment a bundle payload, and
security services have been applied to that bundle, the fragmentation security services have been applied to that bundle, the fragmentation
rules described in [I-D.ietf-dtn-bpbis] MUST be followed. As defined rules described in [I-D.ietf-dtn-bpbis] MUST be followed. As defined
there and summarized here for completeness, only the payload block there and summarized here for completeness, only the payload block
can be fragmented; security blocks, like all extension blocks, can can be fragmented; security blocks, like all extension blocks, can
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Due to the complexity of payload block fragmentation, including the Due to the complexity of payload block fragmentation, including the
possibility of fragmenting payload block fragments, integrity and possibility of fragmenting payload block fragments, integrity and
confidentiality operations are not to be applied to a bundle confidentiality operations are not to be applied to a bundle
representing a fragment. Specifically, a BCB or BIB MUST NOT be representing a fragment. Specifically, a BCB or BIB MUST NOT be
added to a bundle if the "Bundle is a Fragment" flag is set in the added to a bundle if the "Bundle is a Fragment" flag is set in the
Bundle Processing Control Flags field. Bundle Processing Control Flags field.
Security processing in the presence of payload block fragmentation Security processing in the presence of payload block fragmentation
may be handled by other mechanisms outside of the BPSec protocol or may be handled by other mechanisms outside of the BPSec protocol or
by applying BPSec blocks in coordination with an encapsulation by applying BPSec blocks in coordination with an encapsulation
mechanism. mechanism. A node should apply any confidentiality protection prior
to performing any fragmentation.
6. Key Management 6. Key Management
There exist a myriad of ways to establish, communicate, and otherwise There exist a myriad of ways to establish, communicate, and otherwise
manage key information in a DTN. Certain DTN deployments might manage key information in a DTN. Certain DTN deployments might
follow established protocols for key management whereas other DTN follow established protocols for key management whereas other DTN
deployments might require new and novel approaches. BPSec assumes deployments might require new and novel approaches. BPSec assumes
that key management is handled as a separate part of network that key management is handled as a separate part of network
management and this specification neither defines nor requires a management and this specification neither defines nor requires a
specific key management strategy. specific key management strategy.
7. Security Policy Considerations 7. Security Policy Considerations
When implementing BPSec, several policy decisions must be considered. When implementing BPSec, several policy decisions must be considered.
This section describes key policies that affect the generation, This section describes key policies that affect the generation,
forwarding, and receipt of bundles that are secured using this forwarding, and receipt of bundles that are secured using this
specification. No single set of policy decisions is envisioned to specification. No single set of policy decisions is envisioned to
work for all secure DTN deployments. work for all secure DTN deployments.
o If a bundle is received that contains more than one security o If a bundle is received that contains combinations of security
operation, in violation of BPSec, then the BPA must determine how operations that are disallowed by this specification the BPA must
to handle this bundle. The bundle may be discarded, the block determine how to handle the bundle. The bundle may be discarded,
affected by the security operation may be discarded, or one the block affected by the security operation may be discarded, or
security operation may be favored over another. one security operation may be favored over another.
o BPAs in the network must understand what security operations they o BPAs in the network must understand what security operations they
should apply to bundles. This decision may be based on the source should apply to bundles. This decision may be based on the source
of the bundle, the destination of the bundle, or some other of the bundle, the destination of the bundle, or some other
information related to the bundle. information related to the bundle.
o If a waypoint has been configured to add a security operation to a o If a waypoint has been configured to add a security operation to a
bundle, and the received bundle already has the security operation bundle, and the received bundle already has the security operation
applied, then the receiver must understand what to do. The applied, then the receiver must understand what to do. The
receiver may discard the bundle, discard the security target and receiver may discard the bundle, discard the security target and
associated BPSec blocks, replace the security operation, or some associated BPSec blocks, replace the security operation, or some
other action. other action.
o It is recommended that security operations only be applied to the o It is recommended that security operations be considered for every
blocks that absolutely need them. If a BPA were to apply security block in a bundle and that the default behavior of a bundle agent
operations such as integrity or confidentiality to every block in is to use the security services defined in this specification.
the bundle, regardless of need, there could be downstream errors Designers should only deviate from the use of security operations
processing blocks whose contents must be inspected or changed at when the deviation can be justified - such as when doing so causes
every hop along the path. downstream errors when processing blocks whose contents must be
inspected or changed at one or more hops along the path.
o It is recommended that BCBs be allowed to alter the size of o It is recommended that BCBs be allowed to alter the size of
extension blocks and the payload block. However, care must be extension blocks and the payload block. However, care must be
taken to ensure that changing the size of the payload block while taken to ensure that changing the size of the payload block while
the bundle is in transit do not negatively affect bundle the bundle is in transit do not negatively affect bundle
processing (e.g., calculating storage needs, scheduling processing (e.g., calculating storage needs, scheduling
transmission times, caching block byte offsets). transmission times).
o Adding a BIB to a security target that has already been encrypted o Adding a BIB to a security target that has already been encrypted
by a BCB is not allowed. If this condition is likely to be by a BCB is not allowed. If this condition is likely to be
encountered, there are (at least) three possible policies that encountered, there are (at least) three possible policies that
could handle this situation. could handle this situation.
1. At the time of encryption, a plain-text integrity signature 1. At the time of encryption, a security context can be selected
may be generated and added to the BCB for the security target which computes a plain text integrity signature and included
as additional information in the security result field. as a security context result field.
2. The encrypted block may be replicated as a new block and 2. The encrypted block may be replicated as a new block with a
integrity signed. new block number and given integrity protection.
3. An encapsulation scheme may be applied to encapsulate the 3. An encapsulation scheme may be applied to encapsulate the
security target (or the entire bundle) such that the security target (or the entire bundle) such that the
encapsulating structure is, itself, no longer the security encapsulating structure is, itself, no longer the security
target of a BCB and may therefore be the security target of a target of a BCB and may therefore be the security target of a
BIB. BIB.
o It is recommended that security policy address whether cipher o It is recommended that security policy address whether cipher
suites whose cipher-text is larger (or smaller) than the initial suites whose cipher text is larger than the initial plain text are
plain-text are permitted and, if so, for what types of blocks. permitted and, if so, for what types of blocks. Changing the size
Changing the size of a block may cause processing difficulties for of a block may cause processing difficulties for networks that
networks that calculate block offsets into bundles or predict calculate block offsets into bundles or predict transmission times
transmission times or storage availability as a function of bundle or storage availability as a function of bundle size. In other
size. In other cases, changing the size of a payload as part of cases, changing the size of a payload as part of encryption has no
encryption has no significant impact. significant impact.
8. Security Considerations 8. Security Considerations
Given the nature of DTN applications, it is expected that bundles may Given the nature of DTN applications, it is expected that bundles may
traverse a variety of environments and devices which each pose unique traverse a variety of environments and devices which each pose unique
security risks and requirements on the implementation of security security risks and requirements on the implementation of security
within BPSec. For these reasons, it is important to introduce key within BPSec. For these reasons, it is important to introduce key
threat models and describe the roles and responsibilities of the threat models and describe the roles and responsibilities of the
BPSec protocol in protecting the confidentiality and integrity of the BPSec protocol in protecting the confidentiality and integrity of the
data against those threats. This section provides additional data against those threats. This section provides additional
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K_M, K_A, and/or K_B) as well as material which has been publicly- K_M, K_A, and/or K_B) as well as material which has been publicly-
shared. shared.
If Mallory is operating as a privileged node, this is tantamount to If Mallory is operating as a privileged node, this is tantamount to
compromise; BPSec does not provide mechanisms to detect or remove compromise; BPSec does not provide mechanisms to detect or remove
Mallory from the DTN or BPSec secure environment. It is up to the Mallory from the DTN or BPSec secure environment. It is up to the
BPSec implementer or the underlying cryptographic mechanisms to BPSec implementer or the underlying cryptographic mechanisms to
provide appropriate capabilities if they are needed. It should also provide appropriate capabilities if they are needed. It should also
be noted that if the implementation of BPSec uses a single set of be noted that if the implementation of BPSec uses a single set of
shared cryptographic material for all nodes, a legitimate node is shared cryptographic material for all nodes, a legitimate node is
equivalent to a privileged node because K_M == K_A == K_B. equivalent to a privileged node because K_M == K_A == K_B. For this
reason, sharing cryptographic material in this way is not
recommended.
A special case of the legitimate node is when Mallory is either Alice 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 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 able to impersonate traffic as either Alice or Bob, respectively,
traffic to and from that node can be decrypted and encrypted, which means that traffic to and from that node can be decrypted and
respectively. Additionally, messages may be signed as originating encrypted, respectively. Additionally, messages may be signed as
from one of the endpoints. originating from one of the endpoints.
8.2. Attacker Behaviors and BPSec Mitigations 8.2. Attacker Behaviors and BPSec Mitigations
8.2.1. Eavesdropping Attacks 8.2.1. Eavesdropping Attacks
Once Mallory has received a bundle, she is able to examine the Once Mallory has received a bundle, she is able to examine the
contents of that bundle and attempt to recover any protected data or contents of that bundle and attempt to recover any protected data or
cryptographic keying material from the blocks contained within. The cryptographic keying material from the blocks contained within. The
protection mechanism that BPSec provides against this action is the protection mechanism that BPSec provides against this action is the
BCB, which encrypts the contents of its security target, providing BCB, which encrypts the contents of its security target, providing
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confidentiality of the data. Of course, it should be assumed that confidentiality of the data. Of course, it should be assumed that
Mallory is able to attempt offline recovery of encrypted data, so the Mallory is able to attempt offline recovery of encrypted data, so the
cryptographic mechanisms selected to protect the data should provide cryptographic mechanisms selected to protect the data should provide
a suitable level of protection. a suitable level of protection.
When evaluating the risk of eavesdropping attacks, it is important to When evaluating the risk of eavesdropping attacks, it is important to
consider the lifetime of bundles on a DTN. Depending on the network, consider the lifetime of bundles on a DTN. Depending on the network,
bundles may persist for days or even years. Long-lived bundles imply bundles may persist for days or even years. Long-lived bundles imply
that the data exists in the network for a longer period of time and, that the data exists in the network for a longer period of time and,
thus, there may be more opportunities to capture those bundles. thus, there may be more opportunities to capture those bundles.
Additionally, bundles that are long-lived imply that the information Additionally, bundles that are long-lived imply that the information
stored within them may remain relevant and sensitive for long enough stored within them may remain relevant and sensitive for long enough
that, once captured, there is sufficient time to crack encryption that, once captured, there is sufficient time to crack encryption
associated with the bundle. If a bundle does persist on the network associated with the bundle. If a bundle does persist on the network
for years and the cipher suite used for a BCB provides inadequate for years and the cipher suite used for a BCB provides inadequate
protection, Mallory may be able to recover the protected data either protection, Mallory may be able to recover the protected data either
before that bundle reaches its intended destination or before the before that bundle reaches its intended destination or before the
information in the bundle is no longer considered sensitive. information in the bundle is no longer considered sensitive.
NOTE: Mallory is not limited by the bundle lifetime and may retain a
given bundle indefinitely.
NOTE: Irrespective of whether BPSec is used, traffic analysis will be
possible.
8.2.2. Modification Attacks 8.2.2. Modification Attacks
As a node participating in the DTN between Alice and Bob, Mallory As a node participating in the DTN between Alice and Bob, Mallory
will also be able to modify the received bundle, including non-BPSec will also be able to modify the received bundle, including non-BPSec
data such as the primary block, payload blocks, or block processing data such as the primary block, payload blocks, or block processing
control flags as defined in [I-D.ietf-dtn-bpbis]. Mallory will be control flags as defined in [I-D.ietf-dtn-bpbis]. Mallory will be
able to undertake activities which include modification of data able to undertake activities which include modification of data
within the blocks, replacement of blocks, addition of blocks, or within the blocks, replacement of blocks, addition of blocks, or
removal of blocks. Within BPSec, both the BIB and BCB provide removal of blocks. Within BPSec, both the BIB and BCB provide
integrity protection mechanisms to detect or prevent data integrity protection mechanisms to detect or prevent data
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transmission and are expected to be present on receipt. This or transmission and are expected to be present on receipt. This or
other similar out-of-band information is required to correct for other similar out-of-band information is required to correct for
removal of security information in the bundle. removal of security information in the bundle.
A limitation of the BIB may exist within the implementation of BIB A limitation of the BIB may exist within the implementation of BIB
validation at the destination node. If Mallory is a legitimate node 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 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 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 only validating that the BIB was generated by a legitimate user, Bob
will acknowledge the message as originating from Mallory instead of will acknowledge the message as originating from Mallory instead of
Alice. In order to provide verifiable integrity checks, both a BIB Alice. Validating a BIB indicates only that the BIB was generated by
and BCB should be used and the BCB should require an IND-CCA2 a holder of the relevant key; it does not provide any guarantee that
encryption scheme. Such an encryption scheme will guard against the bundle or block was created by the same entity. In order to
signature substitution attempts by Mallory. In this case, Alice provide verifiable integrity checks BCB should require an encryption
creates a BIB with the protected data block as the security target scheme that is Indistinguishable under adaptive Chosen Ciphertext
and then creates a BCB with both the BIB and protected data block as Attack (IND-CCA2) secure. Such an encryption scheme will guard
its security targets. against signature substitution attempts by Mallory. In this case,
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.
8.2.3. Topology Attacks 8.2.3. Topology Attacks
If Mallory is in a MITM position within the DTN, she is able to 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 influence how any bundles that come to her may pass through the
network. Upon receiving and processing a bundle that must be routed network. Upon receiving and processing a bundle that must be routed
elsewhere in the network, Mallory has three options as to how to elsewhere in the network, Mallory has three options as to how to
proceed: not forward the bundle, forward the bundle as intended, or proceed: not forward the bundle, forward the bundle as intended, or
forward the bundle to one or more specific nodes within the network. forward the bundle to one or more specific nodes within the network.
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8.2.4. Message Injection 8.2.4. Message Injection
Mallory is also able to generate new bundles and transmit them into Mallory is also able to generate new bundles and transmit them into
the DTN at will. These bundles may either be copies or slight the DTN at will. These bundles may either be copies or slight
modifications of previously-observed bundles (i.e., a replay attack) modifications of previously-observed bundles (i.e., a replay attack)
or entirely new bundles generated based on the Bundle Protocol, or entirely new bundles generated based on the Bundle Protocol,
BPSec, or other bundle-related protocols. With these attacks BPSec, or other bundle-related protocols. With these attacks
Mallory's objectives may vary, but may be targeting either the bundle Mallory's objectives may vary, but may be targeting either the bundle
protocol or application-layer protocols conveyed by the bundle protocol or application-layer protocols conveyed by the bundle
protocol. protocol. The target could also be the storage and compute of the
nodes running the bundle or application layer protocols (e.g., a
denial of service to flood on the storage of the store-and-forward
mechanism; or compute which would process the packets and perhaps
prevent other activities).
BPSec relies on cipher suite capabilities to prevent replay or forged BPSec relies on cipher suite capabilities to prevent replay or forged
message attacks. A BCB used with appropriate cryptographic message attacks. A BCB used with appropriate cryptographic
mechanisms (e.g., a counter-based cipher mode) may provide replay mechanisms may provide replay protection under certain circumstances.
protection under certain circumstances. Alternatively, application Alternatively, application data itself may be augmented to include
data itself may be augmented to include mechanisms to assert data mechanisms to assert data uniqueness and then protected with a BIB, a
uniqueness and then protected with a BIB, a BCB, or both along with BCB, or both along with other block data. In such a case, the
other block data. In such a case, the receiving node would be able receiving node would be able to validate the uniqueness of the data.
to validate the uniqueness of the data.
9. Security Context Considerations 9. Security Context Considerations
9.1. Identification and Configuration 9.1. Mandating Security Contexts
Because of the diversity of networking scenarios and node
capabilities that may utilize BPSec there is no one security context
mandated for every possible BPSec implementation. For example, a
security context appropriate for a resource-constrained node with
limited connectivity may be inappropriate for use in a well-
resourced, well connected node.
This does not mean that the use of BPSec in a particular network is
meant to be used without security contexts for interoperability and
default behavior. Network designers must identify the minimal set of
security contexts necessary for functions in their network. For
example, a default set of security contexts could be created for use
over the terrestrial Internet and required by any BPSec
implementation communicating over the terrestrial Internet.
Implementations of BPSec MUST support the mandated security contexts
of the networks in which they are applied. If a node serves as a
gateway amongst two or more networks, the BPSec implementation at
that node MUST support the union of security contexts mandated in
those networks.
BPSec has been designed to allow for a diversity of security contexts
and for new contexts to be defined over time. The use of different
security contexts does not change the BPSec protocol itself and the
definition of new security contexts MUST adhere to the requirements
of such contexts as presented in this section and generally in this
specification.
9.2. Identification and Configuration
Security blocks must uniquely define the security context for their Security blocks must uniquely define the security context for their
services. This context MUST be uniquely identifiable and MAY use services. This context MUST be uniquely identifiable and MAY use
parameters for customization. Where policy and configuration parameters for customization. Where policy and configuration
decisions can be captured as parameters, the security context decisions can be captured as parameters, the security context
identifier may identify a cipher suite. In cases where the same identifier may identify a cipher suite. In cases where the same
cipher suites are used with differing predetermined configurations cipher suites are used with differing predetermined configurations
and policies, users can define multiple security contexts that use and policies, users can define multiple security contexts that use
the same cipher suite. the same cipher suite.
skipping to change at page 31, line 35 skipping to change at page 31, line 37
stability, or an increased need for confidentiality, a larger number stability, or an increased need for confidentiality, a larger number
of contexts can be defined with each context supporting few, if any, of contexts can be defined with each context supporting few, if any,
parameters. parameters.
Security Context Examples Security Context Examples
+---------+------------+--------------------------------------------+ +---------+------------+--------------------------------------------+
| Context | Parameters | Definition | | Context | Parameters | Definition |
| Id | | | | Id | | |
+---------+------------+--------------------------------------------+ +---------+------------+--------------------------------------------+
| 1 | Key, IV | AES-GCM-256 cipher suite with provided | | 1 | Encrypted | AES-GCM-256 cipher suite with provided |
| | | ephemeral key and initialization vector. | | | Key, IV | ephemeral key encrypted with a |
| | | predetermined key encryption key and clear |
| | | text initialization vector. |
| 2 | IV | AES-GCM-256 cipher suite with | | 2 | IV | AES-GCM-256 cipher suite with |
| | | predetermined key and predetermined key | | | | predetermined key and predetermined |
| | | rotation policy. | | | | key rotation policy. |
| 3 | Nil | AES-GCM-256 cipher suite with all info | | 3 | Nil | AES-GCM-256 cipher suite with all info |
| | | predetermined. | | | | predetermined. |
+---------+------------+--------------------------------------------+ +---------+------------+--------------------------------------------+
Table 1 Table 1
9.2. Authorship 9.3. Authorship
Developers or implementers should consider the diverse performance Developers or implementers should consider the diverse performance
and conditions of networks on which the Bundle Protocol (and and conditions of networks on which the Bundle Protocol (and
therefore BPSec) will operate. Specifically, the delay and capacity therefore BPSec) will operate. Specifically, the delay and capacity
of delay-tolerant networks can vary substantially. Developers should of delay-tolerant networks can vary substantially. Developers should
consider these conditions to better describe the conditions when consider these conditions to better describe the conditions when
those contexts will operate or exhibit vulnerability, and selection those contexts will operate or exhibit vulnerability, and selection
of these contexts for implementation should be made with of these contexts for implementation should be made with
consideration for this reality. There are key differences that may consideration for this reality. There are key differences that may
limit the opportunity for a security context to leverage existing limit the opportunity for a security context to leverage existing
skipping to change at page 32, line 31 skipping to change at page 32, line 38
time may be extremely large. This may limit the utility of time may be extremely large. This may limit the utility of
session key generation mechanisms, such as Diffie-Hellman, as a session key generation mechanisms, such as Diffie-Hellman, as a
two-way handshake may not be feasible or reliable. two-way handshake may not be feasible or reliable.
o Opportunistic Access: Depending on the application environment, a o Opportunistic Access: Depending on the application environment, a
given endpoint may not be guaranteed to be accessible within a given endpoint may not be guaranteed to be accessible within a
certain amount of time. This may make asymmetric cryptographic certain amount of time. This may make asymmetric cryptographic
architectures which rely on a key distribution center or other architectures which rely on a key distribution center or other
trust center impractical under certain conditions. trust center impractical under certain conditions.
When developing new security contexts for use with BPSec, the When developing security contexts for use with BPSec, the following
following information SHOULD be considered for inclusion in these information SHOULD be considered for inclusion in these
specifications. specifications.
o Security Context Parameters. Security contexts MUST define their o Security Context Parameters. Security contexts MUST define their
parameter Ids, the data types of those parameters, and their CBOR parameter Ids, the data types of those parameters, and their CBOR
encoding. encoding.
o Security Results. Security contexts MUST define their security o Security Results. Security contexts MUST define their security
result Ids, the data types of those results, and their CBOR result Ids, the data types of those results, and their CBOR
encoding. encoding.
o New Canonicalizations. Security contexts may define new o New Canonicalizations. Security contexts may define new
canonicalization algorithms as necessary. canonicalization algorithms as necessary.
o Cipher-Text Size. Security contexts MUST state whether their o Cipher-Text Size. Security contexts MUST state whether their
associated cipher suites generate cipher-text (to include any associated cipher suites generate cipher text (to include any
authentication information) that is of a different size than the authentication information) that is of a different size than the
input plain-text. input plain text.
If a security context does not wish to alter the size of the
plain-text, it should consider defining the following policy.
* Place overflow bytes, authentication signatures, and any If a security context does not wish to alter the size of the plain
additional authenticated data in security result fields rather text it should place overflow bytes and authentication tags in
than in the cipher-text itself. security result fields.
* Pad the cipher-text in cases where the cipher-text is smaller o Block Header Information. Security contexts SHOULD include block
than the plain-text. header information that is considered to be immutable for the
block. This information MAY include the block type code, block
number, CRC Type and CRC field (if present or if missing and
unlikely to be added later), and possibly certain block processing
control flags. Designers should input these fields as additional
data for integrity protection when these fields are expected to
remain unchanged over the path the block will take from the
security source to the security acceptor. Security contexts
considering block header information MUST describe expected
behavior when these fields fail their integrity verification.
10. Defining Other Security Blocks 10. Defining Other Security Blocks
Other security blocks (OSBs) may be defined and used in addition to Other security blocks (OSBs) may be defined and used in addition to
the security blocks identified in this specification. Both the usage the security blocks identified in this specification. Both the usage
of BIB, BCB, and any future OSBs can co-exist within a bundle and can of BIB, BCB, and any future OSBs can co-exist within a bundle and can
be considered in conformance with BPSec if each of the following be considered in conformance with BPSec if each of the following
requirements are met by any future identified security blocks. requirements are met by any future identified security blocks.
o Other security blocks (OSBs) MUST NOT reuse any enumerations o Other security blocks (OSBs) MUST NOT reuse any enumerations
skipping to change at page 34, line 12 skipping to change at page 34, line 24
process an OSB in a bundle fragment that may or may not also process an OSB in a bundle fragment that may or may not also
contain its security target. An OSB definition should also contain its security target. An OSB definition should also
address whether an OSB may be added to a bundle marked as a address whether an OSB may be added to a bundle marked as a
fragment. fragment.
Additionally, policy considerations for the management, monitoring, Additionally, policy considerations for the management, monitoring,
and configuration associated with blocks SHOULD be included in any and configuration associated with blocks SHOULD be included in any
OSB definition. OSB definition.
NOTE: The burden of showing compliance with processing rules is NOTE: The burden of showing compliance with processing rules is
placed upon the standards defining new security blocks and the placed upon the specifications defining new security blocks and the
identification of such blocks shall not, alone, require maintenance identification of such blocks shall not, alone, require maintenance
of this specification. of this specification.
11. IANA Considerations 11. IANA Considerations
This specification includes fields requiring registries managed by This specification includes fields requiring registries managed by
IANA. IANA.
11.1. Bundle Block Types 11.1. Bundle Block Types
This specification allocates two block types from the existing This specification allocates two block types from the existing
"Bundle Block Types" registry defined in [I-D.ietf-dtn-bpbis]. "Bundle Block Types" registry defined in [RFC6255].
Additional Entries for the Bundle Block-Type Codes Registry: Additional Entries for the Bundle Block-Type Codes Registry:
+-------+-----------------------------+---------------+ +-------+-----------------------------+---------------+
| Value | Description | Reference | | Value | Description | Reference |
+-------+-----------------------------+---------------+ +-------+-----------------------------+---------------+
| TBA | Block Integrity Block | This document | | TBA | Block Integrity Block | This document |
| TBA | Block Confidentiality Block | This document | | TBA | Block Confidentiality Block | This document |
+-------+-----------------------------+---------------+ +-------+-----------------------------+---------------+
skipping to change at page 35, line 21 skipping to change at page 35, line 32
+-------+-------------+---------------+ +-------+-------------+---------------+
Table 3 Table 3
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-dtn-bpbis] [I-D.ietf-dtn-bpbis]
Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol
Version 7", draft-ietf-dtn-bpbis-18 (work in progress), Version 7", draft-ietf-dtn-bpbis-22 (work in progress),
January 2020. February 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003, DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>. <https://www.rfc-editor.org/info/rfc3552>.
[RFC6255] Blanchet, M., "Delay-Tolerant Networking Bundle Protocol
IANA Registries", RFC 6255, DOI 10.17487/RFC6255, May
2011, <https://www.rfc-editor.org/info/rfc6255>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>. October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References 12.2. Informative References
[I-D.birrane-dtn-sbsp] [I-D.birrane-dtn-sbsp]
Birrane, E., Pierce-Mayer, J., and D. Iannicca, Birrane, E., Pierce-Mayer, J., and D. Iannicca,
"Streamlined Bundle Security Protocol Specification", "Streamlined Bundle Security Protocol Specification",
draft-birrane-dtn-sbsp-01 (work in progress), October draft-birrane-dtn-sbsp-01 (work in progress), October
2015. 2015.
[I-D.ietf-dtn-bpsec-interop-sc] [I-D.ietf-dtn-bpsec-interop-sc]
Birrane, E., "BPSec Interoperability Security Contexts", Birrane, E., "BPSec Interoperability Security Contexts",
draft-ietf-dtn-bpsec-interop-sc-00 (work in progress), draft-ietf-dtn-bpsec-interop-sc-01 (work in progress),
March 2019. February 2020.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838, DOI 10.17487/RFC4838, Networking Architecture", RFC 4838, DOI 10.17487/RFC4838,
April 2007, <https://www.rfc-editor.org/info/rfc4838>. April 2007, <https://www.rfc-editor.org/info/rfc4838>.
[RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell, [RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell,
"Bundle Security Protocol Specification", RFC 6257, "Bundle Security Protocol Specification", RFC 6257,
DOI 10.17487/RFC6257, May 2011, DOI 10.17487/RFC6257, May 2011,
<https://www.rfc-editor.org/info/rfc6257>. <https://www.rfc-editor.org/info/rfc6257>.
skipping to change at page 36, line 27 skipping to change at page 36, line 44
The following participants contributed technical material, use cases, The following participants contributed technical material, use cases,
and useful thoughts on the overall approach to this security and useful thoughts on the overall approach to this security
specification: Scott Burleigh of the Jet Propulsion Laboratory, Amy specification: Scott Burleigh of the Jet Propulsion Laboratory, Amy
Alford and Angela Hennessy of the Laboratory for Telecommunications Alford and Angela Hennessy of the Laboratory for Telecommunications
Sciences, and Angela Dalton and Cherita Corbett of the Johns Hopkins Sciences, and Angela Dalton and Cherita Corbett of the Johns Hopkins
University Applied Physics Laboratory. University Applied Physics Laboratory.
Authors' Addresses Authors' Addresses
Edward J. Birrane, III Edward J. Birrane, III
The Johns Hopkins University Applied Physics Laboratory The Johns Hopkins University Applied
Physics Laboratory
11100 Johns Hopkins Rd. 11100 Johns Hopkins Rd.
Laurel, MD 20723 Laurel, MD 20723
US US
Phone: +1 443 778 7423 Phone: +1 443 778 7423
Email: Edward.Birrane@jhuapl.edu Email: Edward.Birrane@jhuapl.edu
Kenneth McKeever Kenneth McKeever
The Johns Hopkins University Applied Physics Laboratory The Johns Hopkins University Applied
Physics Laboratory
11100 Johns Hopkins Rd. 11100 Johns Hopkins Rd.
Laurel, MD 20723 Laurel, MD 20723
US US
Phone: +1 443 778 2237 Phone: +1 443 778 2237
Email: Ken.McKeever@jhuapl.edu Email: Ken.McKeever@jhuapl.edu
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