Delay-Tolerant Networking E.J. Birrane
Internet-Draft A. White
Intended status: Standards Track S. Heiner
Expires: 26 January 2022 JHU/APL
25 July 2021
BPSec Default Security Contexts
draft-ietf-dtn-bpsec-default-sc-11
Abstract
This document defines default integrity and confidentiality security
contexts that can be used with the Bundle Protocol Security Protocol
(BPSec) implementations. These security contexts are intended to be
used for both testing the interoperability of BPSec implementations
and for providing basic security operations when no other security
contexts are defined or otherwise required for a network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 26 January 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Integrity Security Context BIB-HMAC-SHA2 . . . . . . . . . . 4
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Parameters . . . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. SHA Variant . . . . . . . . . . . . . . . . . . . . . 7
3.3.2. Wrapped Key . . . . . . . . . . . . . . . . . . . . . 7
3.3.3. Integrity Scope Flags . . . . . . . . . . . . . . . . 8
3.3.4. Enumerations . . . . . . . . . . . . . . . . . . . . 8
3.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.5. Key Considerations . . . . . . . . . . . . . . . . . . . 9
3.6. Security Processing Considerations . . . . . . . . . . . 10
3.7. Canonicalization Algorithms . . . . . . . . . . . . . . . 10
3.8. Processing . . . . . . . . . . . . . . . . . . . . . . . 11
3.8.1. Keyed Hash Generation . . . . . . . . . . . . . . . . 11
3.8.2. Keyed Hash Verification . . . . . . . . . . . . . . . 12
4. Security Context BCB-AES-GCM . . . . . . . . . . . . . . . . 13
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.3. Parameters . . . . . . . . . . . . . . . . . . . . . . . 16
4.3.1. Initialization Vector (IV) . . . . . . . . . . . . . 16
4.3.2. AES Variant . . . . . . . . . . . . . . . . . . . . . 16
4.3.3. Wrapped Key . . . . . . . . . . . . . . . . . . . . . 17
4.3.4. AAD Scope Flags . . . . . . . . . . . . . . . . . . . 17
4.3.5. Enumerations . . . . . . . . . . . . . . . . . . . . 18
4.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.4.1. Authentication Tag . . . . . . . . . . . . . . . . . 19
4.4.2. Enumerations . . . . . . . . . . . . . . . . . . . . 20
4.5. Key Considerations . . . . . . . . . . . . . . . . . . . 20
4.6. GCM Considerations . . . . . . . . . . . . . . . . . . . 21
4.7. Canonicalization Algorithms . . . . . . . . . . . . . . . 22
4.7.1. Cipher text related calculations . . . . . . . . . . 22
4.7.2. Additional Authenticated Data . . . . . . . . . . . . 23
4.8. Processing . . . . . . . . . . . . . . . . . . . . . . . 24
4.8.1. Encryption . . . . . . . . . . . . . . . . . . . . . 24
4.8.2. Decryption . . . . . . . . . . . . . . . . . . . . . 26
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5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
5.1. Security Context Identifiers . . . . . . . . . . . . . . 27
5.2. Integrity Scope Flags . . . . . . . . . . . . . . . . . . 27
5.3. AAD Scope Flags . . . . . . . . . . . . . . . . . . . . . 28
5.4. Guidance for Designated Experts . . . . . . . . . . . . . 29
6. Security Considerations . . . . . . . . . . . . . . . . . . . 29
6.1. Key Management . . . . . . . . . . . . . . . . . . . . . 30
6.2. Key Handling . . . . . . . . . . . . . . . . . . . . . . 31
6.3. AES GCM . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.4. AES Key Wrap . . . . . . . . . . . . . . . . . . . . . . 32
6.5. Bundle Fragmentation . . . . . . . . . . . . . . . . . . 32
7. Normative References . . . . . . . . . . . . . . . . . . . . 33
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 34
A.1. Example 1: Simple Integrity . . . . . . . . . . . . . . . 35
A.1.1. Original Bundle . . . . . . . . . . . . . . . . . . . 35
A.1.2. Security Operation Overview . . . . . . . . . . . . . 37
A.1.3. Bundle Integrity Block . . . . . . . . . . . . . . . 38
A.1.4. Final Bundle . . . . . . . . . . . . . . . . . . . . 39
A.2. Example 2: Simple Confidentiality with Key Wrap . . . . . 39
A.2.1. Original Bundle . . . . . . . . . . . . . . . . . . . 39
A.2.2. Security Operation Overview . . . . . . . . . . . . . 40
A.2.3. Bundle Confidentiality Block . . . . . . . . . . . . 41
A.2.4. Final Bundle . . . . . . . . . . . . . . . . . . . . 43
A.3. Example 3: Security Blocks from Multiple Sources . . . . 43
A.3.1. Original Bundle . . . . . . . . . . . . . . . . . . . 43
A.3.2. Security Operation Overview . . . . . . . . . . . . . 45
A.3.3. Bundle Integrity Block . . . . . . . . . . . . . . . 45
A.3.4. Bundle Confidentiality Block . . . . . . . . . . . . 47
A.3.5. Final Bundle . . . . . . . . . . . . . . . . . . . . 49
A.4. Example 4: Security Blocks with Full Scope . . . . . . . 49
A.4.1. Original Bundle . . . . . . . . . . . . . . . . . . . 49
A.4.2. Security Operation Overview . . . . . . . . . . . . . 50
A.4.3. Bundle Integrity Block . . . . . . . . . . . . . . . 51
A.4.4. Bundle Confidentiality Block . . . . . . . . . . . . 52
A.4.5. Final Bundle . . . . . . . . . . . . . . . . . . . . 55
Appendix B. CDDL Expression . . . . . . . . . . . . . . . . . . 55
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 56
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
1. Introduction
The Bundle Protocol Security Protocol (BPSec) [I-D.ietf-dtn-bpsec]
specification provides inter-bundle integrity and confidentiality
operations for networks deploying the Bundle Protocol (BP)
[I-D.ietf-dtn-bpbis]. BPSec defines BP extension blocks to carry
security information produced under the auspices of some security
context.
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This document defines two security contexts (one for an integrity
service and one for a confidentiality service) for populating BPSec
Block Integrity Blocks (BIBs) and Block Confidentiality Blocks
(BCBs). This document assumes familiarity with the concepts and
terminology associated with BP and BPSec, as these security contexts
are used with BPSec security blocks and other BP blocks carried
within BP bundles.
These contexts generate information that MUST be encoded using the
CBOR specification documented in [RFC8949].
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Integrity Security Context BIB-HMAC-SHA2
3.1. Overview
The BIB-HMAC-SHA2 security context provides a keyed-hash Message
Authentication Code (MAC) over a set of plain text information. This
context uses the Secure Hash Algorithm 2 (SHA-2) discussed in [SHS]
combined with the HMAC keyed hash discussed in [RFC2104]. The
combination of HMAC and SHA-2 as the integrity mechanism for this
security context was selected for two reasons:
1. The use of symmetric keys allows this security context to be used
in places where an asymmetric-key infrastructure (such as a
public key infrastructure) might be impractical.
2. The combination HMAC-SHA2 represents a well-supported and well-
understood integrity mechanism with multiple implementations
available.
BIB-HMAC-SHA2 supports three variants of HMAC-SHA, based on the
supported length of the SHA-2 hash value. These variants correspond
to "HMAC 256/256", "HMAC 384/384", and "HMAC 512/512" as defined in
[RFC8152] Table 7: HMAC Algorithm Values. The selection of which
variant is used by this context is provided as a security context
parameter.
The output of the HMAC MUST be equal to the size of the SHA2 hashing
function: 256 bits for SHA-256, 384 bits for SHA-384, and 512 bits
for SHA-512.
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The BIB-HMAC-SHA2 security context MUST have the security context
identifier specified in Section 5.1.
3.2. Scope
The scope of BIB-HMAC-SHA2 is the set of information used to produce
the plain text over which a keyed hash is calculated. This plain
text is termed the "Integrity Protected Plain Text" (IPPT). The
content of the IPPT is constructed as the concatenation of
information whose integrity is being preserved from the BIB-HMAC-SHA2
security source to its security acceptor. There are five types of
information that can be used in the generation of the IPPT, based on
how broadly the concept of integrity is being applied. These five
types of information, whether they are required, and why they are
important for integrity, are discussed as follows.
Security target contents
The contents of the block-type-specific data field of the
security target MUST be included in the IPPT. Including this
information protects the security target data and is considered
the minimal, required set of information for an integrity service
on the security target.
IPPT Scope
The determination of which optional types of information were
used when constructing the IPPT MUST, itself, always be included
in the IPPT. Including this information ensures that the scope
of the IPPT construction at a security source matches the scope
of the IPPT construction at security verifiers and security
acceptors.
Primary block
The primary block identifies a bundle and, once created, the
contents of this block are immutable. Changes to the primary
block associated with the security target indicate that the
security target (and BIB) might no longer be in the correct
bundle.
For example, if a security target and associated BIB are copied
from one bundle to another bundle, the BIB might still contain a
verifiable signature for the security target unless information
associated with the bundle primary block is included in the keyed
hash carried by the BIB.
Including this information in the IPPT protects the integrity of
the association of the security target with a specific bundle.
Security target other fields
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The other fields of the security target include block
identification and processing information. Changing this
information changes how the security target is treated by nodes
in the network even when the "user data" of the security target
are otherwise unchanged.
For example, if the block processing control flags of a security
target are different at a security verifier than they were
originally set at the security source then the policy for
handling the security target has been modified.
Including this information in the IPPT protects the integrity of
the policy and identification of the security target data.
BIB other fields
The other fields of the BIB include block identification and
processing information. Changing this information changes how
the BIB is treated by nodes in the network, even when other
aspects of the BIB are unchanged.
For example, if the block processing control flags of the BIB are
different at a security verifier than they were originally set at
the security source, then the policy for handling the BIB has
been modified.
Including this information in the IPPT protects the integrity of
the policy and identification of the security service in the
bundle.
NOTE: The security context identifier and security context
parameters of the security block are not included in the IPPT
because these parameters, by definition, are required to verify
or accept the security service. Successful verification at
security verifiers and security acceptors implies that these
parameters were unchanged since being specified at the security
source. This is the case because keys cannot be re-used across
security contexts, and because the integrity scope flags used to
define the IPPT are included in the IPPT itself.
The scope of the BIB-HMAC-SHA2 security context is configured using
an optional security context parameter.
3.3. Parameters
BIB-HMAC-SHA2 can be parameterized to select SHA-2 variants,
communicate key information, and define the scope of the IPPT.
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3.3.1. SHA Variant
This optional parameter identifies which variant of the SHA-2
algorithm is to be used in the generation of the authentication code.
This value MUST be encoded as a CBOR unsigned integer.
Valid values for this parameter are as follows.
SHA Variant Parameter Values
+=======+======================================+
| Value | Description |
+=======+======================================+
| 5 | HMAC 256/256 as defined in [RFC8152] |
| | Table 7: HMAC Algorithm Values |
+-------+--------------------------------------+
| 6 | HMAC 384/384 as defined in [RFC8152] |
| | Table 7: HMAC Algorithm Values |
+-------+--------------------------------------+
| 7 | HMAC 512/512 as defined in [RFC8152] |
| | Table 7: HMAC Algorithm Values |
+-------+--------------------------------------+
Table 1
When not provided, implementations SHOULD assume a value of 6
(indicating use of HMAC 384/384), unless an alternate default is
established by local security policy at the security source,
verifiers, or acceptor of this integrity service.
3.3.2. Wrapped Key
This optional parameter contains the output of the AES key wrap
authenticated encryption function (KW-AE) as defined in [RFC5649].
Specifically, this parameter holds the cipher text produced when
running the KW-AE algorithm with the input string being the symmetric
HMAC key used to generate the security results present in the
security block. The value of this parameter is used as input to the
AES key wrap authenticated decryption function (KW-AD) at security
verifiers and security acceptors to determine the symmetric HMAC key
needed for the proper validation of the security results in the
security block.
This value MUST be encoded as a CBOR byte string.
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If this parameter is not present then security verifiers and
acceptors MUST determine the proper key as a function of their local
BPSec policy and configuration.
3.3.3. Integrity Scope Flags
This optional parameter contains a series of flags that describe what
information is to be included with the block-type-specific data when
constructing the IPPT value.
This value MUST be represented as a CBOR unsigned integer, the value
of which MUST be processed as a 16-bit field. The maximum value of
this field, as a CBOR unsigned integer, MUST be 65535.
Implementations MUST set reserved and unassigned bits in this field
to 0 when constructing these flags at a security source. Once set,
the value of this field MUST NOT be altered until the security
service is completed at the security acceptor in the network and
removed from the bundle.
Bits in this field represent additional information to be included
when generating an integrity signature over the security target.
These bits are defined as follows.
- Bit 0 (the low-order bit, 0x0001): Primary Block Flag.
- Bit 1 (0x0002): Target Header Flag.
- Bit 2 (0x0004): Security Header Flag.
- Bits 3-7 are reserved.
- Bits 8-15 are unassigned.
3.3.4. Enumerations
The BIB-HMAC-SHA2 security context parameters are listed in Table 2.
In this table, the "Parm Id" column refers to the expected Parameter
Identifier described in [I-D.ietf-dtn-bpsec], Section 3.10 "Parameter
and Result Identification".
If the default value column is empty, this indicates that the
security parameter does not have a default value.
BIB-HMAC-SHA2 Security Parameters
+=========+=============+====================+===============+
| Parm Id | Parm Name | CBOR Encoding Type | Default Value |
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+=========+=============+====================+===============+
| 1 | SHA Variant | unsigned integer | 6 |
+---------+-------------+--------------------+---------------+
| 2 | Wrapped Key | Byte String | |
+---------+-------------+--------------------+---------------+
| 3 | Integrity | unsigned integer | 7 |
| | Scope Flags | | |
+---------+-------------+--------------------+---------------+
Table 2
3.4. Results
The BIB-HMAC-SHA2 security context results are listed in Table 3. In
this table, the "Result Id" column refers to the expected Result
Identifier described in [I-D.ietf-dtn-bpsec], Section 3.10 "Parameter
and Result Identification".
BIB-HMAC-SHA2 Security Results
+========+==========+===============+======================+
| Result | Result | CBOR Encoding | Description |
| Id | Name | Type | |
+========+==========+===============+======================+
| 1 | Expected | byte string | The output of the |
| | HMAC | | HMAC calculation at |
| | | | the security source. |
+--------+----------+---------------+----------------------+
Table 3
3.5. Key Considerations
HMAC keys used with this context MUST be symmetric and MUST have a
key length equal to the output of the HMAC. For this reason, HMAC
key lengths will be integer divisible by 8 bytes and special padding-
aware AES key wrap algorithms are not needed.
It is assumed that any security verifier or security acceptor
performing an integrity verification can determine the proper HMAC
key to be used. Potential sources of the HMAC key include (but are
not limited to) the following:
Pre-placed keys selected based on local policy.
Keys extracted from material carried in the BIB.
Session keys negotiated via a mechanism external to the BIB.
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When an AES-KW wrapped key is present in a security block, it is
assumed that security verifiers and security acceptors can
independently determine the key encryption key (KEK) used in the
wrapping of the symmetric HMAC key.
As discussed in Section 6 and emphasized here, it is strongly
recommended that keys be protected once generated, both when they are
stored and when they are transmitted.
3.6. Security Processing Considerations
An HMAC calculated over the same IPPT with the same key will always
have the same value. This regularity can lead to practical side-
channel attacks whereby an attacker could produce known plain text
and a guess at an HMAC tag and observe the behavior of a verifier.
With a modest number of trials, a side-channel attack could produce
an HMAC tag for attacher-provided plain text without the attacker
ever knowing the HMAC key.
A common method of observing the behavior of a verifier is precise
analysis of the timing associated with comparisons. Therefore, one
way to prevent behavior analysis of this type is to ensure that any
comparisons of the supplied and expected authentication tag occur in
constant time.
A constant-time comparison function SHOULD be used for the comparison
of authentication tags by any implementation of this security
context. In cases where such a function is difficult or impossible
to use, the impact of side-channel (in general) and timing attacks
(specifically) need to be considered as part of the implementation.
3.7. Canonicalization Algorithms
This section defines the canonicalization algorithm used to prepare
the IPPT input to the BIB-HMAC-SHA2 integrity mechanism. The
construction of the IPPT depends on the settings of the integrity
scope flags that can be provided as part of customizing the behavior
of this security context.
In all cases, the canonical form of any portion of an extension block
MUST be performed as described in [I-D.ietf-dtn-bpsec]. The
canonicalization algorithms defined in [I-D.ietf-dtn-bpsec] adhere to
the canonical forms for extension blocks defined in
[I-D.ietf-dtn-bpbis] but resolve ambiguities related to how values
are represented in CBOR.
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The IPPT is constructed using the following process. While integrity
scope flags might not be included in the BIB representing the
security operation, they MUST be included in the IPPT value itself.
1. The canonical form of the IPPT starts as the CBOR encoding of the
integrity scope flags in which all unset flags, reserved bits,
and unassigned bits have been set to 0. For example, if the
primary block flag, target header flag, and security header flag
are each set, then the initial value of the canonical form of the
IPPT will be 0x07.
2. If the primary block flag of the integrity scope flags is set to
1, then a canonical form of the bundle's primary block MUST be
calculated and the result appended to the IPPT.
3. If the target header flag of the integrity scope flags is set to
1, then the canonical form of the block type code, block number,
and block processing control flags associated with the security
target MUST be calculated and, in that order, appended to the
IPPT.
4. If the security header flag of the integrity scope flags is set
to 1, then the canonical form of the block type code, block
number, and block processing control flags associated with the
BIB MUST be calculated and, in that order, appended to the IPPT.
5. The canonical form of the security target block-type-specific
data MUST be calculated and appended to the IPPT.
3.8. Processing
3.8.1. Keyed Hash Generation
During keyed hash generation, two inputs are prepared for the the
appropriate HMAC/SHA2 algorithm: the HMAC key and the IPPT. These
data items MUST be generated as follows.
The HMAC key MUST have the appropriate length as required by local
security policy. The key can be generated specifically for this
integrity service, given as part of local security policy, or
through some other key management mechanism as discussed in
Section 3.5.
Prior to the generation of the IPPT, if a CRC value is present for
the target block of the BIB, then that CRC value MUST be removed
from the target block. This involves both removing the CRC value
from the target block and setting the CRC Type field of the target
block to "no CRC is present."
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Once CRC information is removed, the IPPT MUST be generated as
discussed in Section 3.7.
Upon successful hash generation the following actions MUST occur.
The keyed hash produced by the HMAC/SHA2 variant MUST be added as
a security result for the BIB representing the security operation
on this security target, as discussed in Section 3.4.
Finally, the BIB containing information about this security operation
MUST be updated as follows. These operations can occur in any order.
The security context identifier for the BIB MUST be set to the
context identifier for BIB-HMAC-SHA2.
Any local flags used to generate the IPPT MUST be placed in the
integrity scope flags security parameter for the BIB unless these
flags are expected to be correctly configured at security
verifiers and acceptors in the network.
The HMAC key MAY be included as a security parameter in which case
it MUST be wrapped using the NIST AES-KW algorithm and the results
of the wrapping added as the wrapped key security parameter for
the BIB.
The SHA variant used by this security context SHOULD be added as
the SHA variant security parameter for the BIB if it differs from
the default key length. Otherwise, this parameter MAY be omitted
if doing so provides a useful reduction in message sizes.
Problems encountered in the keyed hash generation MUST be processed
in accordance with local BPSec security policy.
3.8.2. Keyed Hash Verification
During keyed hash verification, the input of the security target and
a HMAC key are provided to the appropriate HMAC/SHA2 algorithm.
During keyed hash verification, two inputs are prepared for the
appropriate HMAC/SHA2 algorithm: the HMAC key and the IPPT. These
data items MUST be generated as follows.
The HMAC key MUST be derived using the wrapped key security
parameter if such a parameter is included in the security context
parameters of the BIB. Otherwise, this key MUST be derived in
accordance with security policy at the verifying node as discussed
in Section 3.5.
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The IPPT MUST be generated as discussed in Section 3.7 with the
value of integrity scope flags being taken from the integrity
scope flags security context parameter. If the integrity scope
flags parameter is not included in the security context parameters
then these flags MAY be derived from local security policy.
The calculated HMAC output MUST be compared to the expected HMAC
output encoded in the security results of the BIB for the security
target. If the calculated HMAC and expected HMAC are identical, the
verification MUST be considered a success. Otherwise, the
verification MUST be considered a failure.
If the verification fails or otherwise experiences an error, or if
any needed parameters are missing, then the verification MUST be
treated as failed and processed in accordance with local security
policy.
This security service is removed from the bundle at the security
acceptor as required by the BPSec specification. If the security
acceptor is not the bundle destination and if no other integrity
service is being applied to the target block, then a CRC MUST be
included for the target block. The CRC type, as determined by
policy, is set in the target block's CRC type field and the
corresponding CRC value is added as the CRC field for that block.
4. Security Context BCB-AES-GCM
4.1. Overview
The BCB-AES-GCM security context replaces the block-type-specific
data field of its security target with cipher text generated using
the Advanced Encryption Standard (AES) cipher operating in Galois/
Counter Mode (GCM) [AES-GCM]. The use of AES-GCM was selected as the
cipher suite for this confidentiality mechanism for several reasons:
1. The selection of a symmetric-key cipher suite allows for
relatively smaller keys than asymmetric-key cipher suites.
2. The selection of a symmetric-key cipher suite allows this
security context to be used in places where an asymmetric-key
infrastructure (such as a public key infrastructure) might be
impractical.
3. The use of the Galois/Counter Mode produces cipher-text with the
same size as the plain text making the replacement of target
block information easier as length fields do not need to be
changed.
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4. The AES-GCM cipher suite provides authenticated encryption, as
required by the BPSec protocol.
Additionally, the BCB-AES-GCM security context generates an
authentication tag based on the plain text value of the block-type-
specific data and other additional authenticated data that might be
specified via parameters to this security context.
This security context supports two variants of AES-GCM, based on the
supported length of the symmetric key. These variants correspond to
A128GCM and A256GCM as defined in [RFC8152] Table 9: Algorithm Value
for AES-GCM.
The BCB-AES-GCM security context MUST have the security context
identifier specified in Section 5.1.
4.2. Scope
There are two scopes associated with BCB-AES-GCM: the scope of the
confidentiality service and the scope of the authentication service.
The first defines the set of information provided to the AES-GCM
cipher for the purpose of producing cipher text. The second defines
the set of information used to generate an authentication tag.
The scope of the confidentiality service defines the set of
information provided to the AES-GCM cipher for the purpose of
producing cipher text. This MUST be the full set of plain text
contained in the block-type-specific data field of the security
target.
The scope of the authentication service defines the set of
information used to generate an authentication tag carried with the
security block. This information contains all data protected by the
confidentiality service, the scope flags used to identify other
optional information, and MAY include other information (additional
authenticated data), as follows.
Primary block
The primary block identifies a bundle and, once created, the
contents of this block are immutable. Changes to the primary
block associated with the security target indicate that the
security target (and BCB) might no longer be in the correct
bundle.
For example, if a security target and associated BCB are copied
from one bundle to another bundle, the BCB might still be able to
decrypt the security target even though these blocks were never
intended to exist in the copied-to bundle.
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Including this information as part of additional authenticated
data ensures that security target (and security block) appear in
the same bundle at the time of decryption as at the time of
encryption.
Security target other fields
The other fields of the security target include block
identification and processing information. Changing this
information changes how the security target is treated by nodes
in the network even when the "user data" of the security target
are otherwise unchanged.
For example, if the block processing control flags of a security
target are different at a security verifier than they were
originally set at the security source then the policy for
handling the security target has been modified.
Including this information as part of additional authenticated
data ensures that the cipher text in the security target will not
be used with a different set of block policy than originally set
at the time of encryption.
BCB other fields
The other fields of the BCB include block identification and
processing information. Changing this information changes how
the BCB is treated by nodes in the network, even when other
aspects of the BCB are unchanged.
For example, if the block processing control flags of the BCB are
different at a security acceptor than they were originally set at
the security source then the policy for handling the BCB has been
modified.
Including this information as part of additional authenticated
data ensures that the policy and identification of the security
service in the bundle has not changed.
NOTE: The security context identifier and security context
parameters of the security block are not included as additional
authenticated data because these parameters, by definition, are
those needed to verify or accept the security service.
Therefore, it is expected that changes to these values would
result in failures at security verifiers and security acceptors.
This is the case because keys cannot be re-used across security
contexts, and because the AAD scope flags used to identify the
AAD are included in the AAD.
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The scope of the BCB-AES-GCM security context is configured using an
optional security context parameter.
4.3. Parameters
BCB-AES-GCM can be parameterized to specify the AES variant,
initialization vector, key information, and identify additional
authenticated data.
4.3.1. Initialization Vector (IV)
This optional parameter identifies the initialization vector (IV)
used to initialize the AES-GCM cipher.
The length of the initialization vector, prior to any CBOR encoding,
MUST be between 8-16 bytes. A value of 12 bytes SHOULD be used
unless local security policy requires a different length.
This value MUST be encoded as a CBOR byte string.
The initialization vector can have any value with the caveat that a
value MUST NOT be re-used for multiple encryptions using the same
encryption key. This value MAY be re-used when encrypting with
different keys. For example, if each encryption operation using BCB-
AES-GCM uses a newly generated key, then the same IV can be reused.
4.3.2. AES Variant
This optional parameter identifies the AES variant being used for the
AES-GCM encryption, where the variant is identified by the length of
key used.
This value MUST be encoded as a CBOR unsigned integer.
Valid values for this parameter are as follows.
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AES Variant Parameter Values
+=======+=======================================+
| Value | Description |
+=======+=======================================+
| 1 | A128GCM as defined in [RFC8152] |
| | Table 9: Algorithm Values for AES-GCM |
+-------+---------------------------------------+
| 3 | A256GCM as defined in [RFC8152] |
| | Table 9: Algorithm Values for AES-GCM |
+-------+---------------------------------------+
Table 4
When not provided, implementations SHOULD assume a value of 3
(indicating use of A256GCM), unless an alternate default is
established by local security policy at the security source,
verifier, or acceptor of this integrity service.
Regardless of the variant, the generated authentication tag MUST
always be 128 bits.
4.3.3. Wrapped Key
This optional parameter contains the output of the AES key wrap
authenticated encryption function (KW-AE) as defined in [RFC5649].
Specifically, this parameter holds the cipher text produced when
running the KW-AE algorithm with the input string being the symmetric
AES key used to generate the security results present in the security
block. The value of this parameter is used as input to the AES key
wrap authenticated decryption function (KW-AD) at security verifiers
and security acceptors to determine the symmetric AES key needed for
the proper decryption of the security results in the security block.
This value MUST be encoded as a CBOR byte string.
If this parameter is not present then security verifiers and
acceptors MUST determine the proper key as a function of their local
BPSec policy and configuration.
4.3.4. AAD Scope Flags
This optional parameter contains a series of flags that describe what
information is to be included with the block-type-specific data of
the security target as part of additional authenticated data (AAD).
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This value MUST be represented as a CBOR unsigned integer, the value
of which MUST be processed as a 16-bit field. The maximum value of
this field, as a CBOR unsigned integer, MUST be 65535.
Implementations MUST set reserved and unassigned bits in this field
to 0 when constructing these flags at a security source. Once set,
the value of this field MUST NOT be altered until the security
service is completed at the security acceptor in the network and
removed from the bundle.
Bits in this field represent additional information to be included
when generating an integrity signature over the security target.
These bits are defined as follows.
- Bit 0 (the low-order bit, 0x0001): Primary Block Flag.
- Bit 1 (0x0002): Target Header Flag.
- Bit 2 (0x0004): Security Header Flag.
- Bits 3-7 are reserved.
- Bits 8-15 are unassigned.
4.3.5. Enumerations
The BCB-AES-GCM security context parameters are listed in Table 5.
In this table, the "Parm Id" column refers to the expected Parameter
Identifier described in [I-D.ietf-dtn-bpsec], Section 3.10 "Parameter
and Result Identification".
If the default value column is empty, this indicates that the
security parameter does not have a default value.
BCB-AES-GCM Security Parameters
+=========+================+====================+===============+
| Parm Id | Parm Name | CBOR Encoding Type | Default Value |
+=========+================+====================+===============+
| 1 | Initialization | Byte String | |
| | Vector | | |
+---------+----------------+--------------------+---------------+
| 2 | AES Variant | Unsigned Integer | 3 |
+---------+----------------+--------------------+---------------+
| 3 | Wrapped Key | Byte String | |
+---------+----------------+--------------------+---------------+
| 4 | AAD Scope | Unsigned Integer | 7 |
| | Flags | | |
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+---------+----------------+--------------------+---------------+
Table 5
4.4. Results
The BCB-AES-GCM security context produces a single security result
carried in the security block: the authentication tag.
NOTES:
* The cipher text generated by the cipher suite is not considered a
security result as it is stored in the block-type-specific data
field of the security target block. When operating in GCM mode,
AES produces cipher text of the same size as its plain text and,
therefore, no additional logic is required to handle padding or
overflow caused by the encryption in most cases (see below).
* If the authentication tag can be separated from the cipher text,
then the tag MAY be separated and stored in the authentication tag
security result field. Otherwise, the security target block MUST
be resized to accommodate the additional 128 bits of
authentication tag included with the generated cipher text
replacing the block-type-specific-data field of the security
target block.
4.4.1. Authentication Tag
The authentication tag is generated by the cipher suite over the
security target plain text input to the cipher suite as combined with
any optional additional authenticated data. This tag is used to
ensure that the plain text (and important information associated with
the plain text) is authenticated prior to decryption.
If the authentication tag is included in the cipher text placed in
the security target block-type-specific data field, then this
security result MUST NOT be included in the BCB for that security
target.
The length of the authentication tag, prior to any CBOR encoding,
MUST be 128 bits.
This value MUST be encoded as a CBOR byte string.
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4.4.2. Enumerations
The BCB-AES-GCM security context results are listed in Table 6. In
this table, the "Result Id" column refers to the expected Result
Identifier described in [I-D.ietf-dtn-bpsec], Section 3.10 "Parameter
and Result Identification".
BCB-AES-GCM Security Results
+===========+====================+====================+
| Result Id | Result Name | CBOR Encoding Type |
+===========+====================+====================+
| 1 | Authentication Tag | Byte String |
+-----------+--------------------+--------------------+
Table 6
4.5. Key Considerations
Keys used with this context MUST be symmetric and MUST have a key
length equal to the key length defined in the security context
parameters or as defined by local security policy at security
verifiers and acceptors. For this reason, content-encrypting key
lengths will be integer divisible by 8 bytes and special padding-
aware AES key wrap algorithms are not needed.
It is assumed that any security verifier or security acceptor can
determine the proper key to be used. Potential sources of the key
include (but are not limited to) the following.
Pre-placed keys selected based on local policy.
Keys extracted from material carried in the BCB.
Session keys negotiated via a mechanism external to the BCB.
When an AES-KW wrapped key is present in a security block, it is
assumed that security verifiers and security acceptors can
independently determine the key encryption key (KEK) used in the
wrapping of the symmetric AES content-encrypting key.
The security provided by block ciphers is reduced as more data is
processed with the same key. The total number of AES blocks
processed with a single key for AES-GCM is recommended to be less
than 2^64, as described in Appendix B of [AES-GCM].
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Additionally, there exist limits on the number of encryptions that
can be performed with the same key. The total number of invocations
of the authenticated encryption function with a single key for AES-
GCM is required to not exceed 2^32, as described in Section 8.3 of
[AES-GCM].
As discussed in Section 6 and emphasized here, it is strongly
recommended that keys be protected once generated, both when they are
stored and when they are transmitted.
4.6. GCM Considerations
The GCM cryptographic mode of AES has specific requirements that MUST
be followed by implementers for the secure function of the BCB-AES-
GCM security context. While these requirements are well documented
in [AES-GCM], some of them are repeated here for emphasis.
With the exception of the AES-KW function, the IVs used by the
BCB-AES-GCM security context are considered to be per-invocation
IVs. The pairing of a per-invocation IV and a security key MUST
be unique. A per-invocation IV MUST NOT be used with a security
key more than one time. If a per-invocation IV and key pair are
repeated then the GCM implementation is vulnerable to forgery
attacks. Because the loss of integrity protection occurs with
even a single reuse, this situation is often considered to have
catastrophic security consequences. More information regarding
the importance of the uniqueness of the IV value can be found in
Appendix A of [AES-GCM].
Methods of generating unique IV values are provided in Chapter 8
of [AES-GCM]. For example, one method decomposes the IV value
into a fixed field and an invocation field. The fixed field being
a constant value associated with a device and the invocation field
changing on each invocation (such as by incrementing an integer
counter). Implementers SHOULD carefully read all relevant
sections of [AES-GCM] when generating any mechanism to create
unique IVs.
The AES-KW function used to wrap keys for the security contexts in
this document uses a single, globally constant IV input to the AES
cipher operation and, thus, is distinct from the aforementioned
requirement related to per-invocation IVs.
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While any tag-based authentication mechanism has some likelihood
of being forged, this probability is increased when using AES-GCM.
In particular, short tag lengths combined with very long messages
SHOULD be avoided when using this mode. The BCB-AES-GCM security
context requires the use of 128-bit authentication tags at all
times. Concerns relating to the size of authentication tags is
discussed in Appendices B and C of [AES-GCM].
As discussed in Appendix B of [AES-GCM], implementations SHOULD
limit the number of unsuccessful verification attempts for each
key to reduce the likelihood of guessing tag values. This type of
check has potential state-keeping issues when AES-KW is used,
since an attacker could cause a large number of keys to have been
used at least once.
As discussed in the Security Considerations section of
[I-D.ietf-dtn-bpsec], delay-tolerant networks have a higher
occurrence of replay attacks due to the store-and-forward nature
of the network. Because GCM has no inherent replay attack
protection, implementors SHOULD attempt to detect replay attacks
by using mechanisms such as those described in Appendix D of
[AES-GCM].
4.7. Canonicalization Algorithms
This section defines the canonicalization algorithms used to prepare
the inputs used to generate both the cipher text and the
authentication tag.
In all cases, the canonical form of any portion of an extension block
MUST be performed as described in [I-D.ietf-dtn-bpsec]. The
canonicalization algorithms defined in [I-D.ietf-dtn-bpsec] adhere to
the canonical forms for extension blocks defined in
[I-D.ietf-dtn-bpbis] but resolve ambiguities related to how values
are represented in CBOR.
4.7.1. Cipher text related calculations
The BCB operates over the block-type-specific data of a block, but
the BP always encodes these data within a single, definite-length
CBOR byte string. Therefore, the plain text used during encryption
MUST be calculated as the value of the block-type-specific data field
of the security target excluding the BP CBOR encoding.
Consider the following two CBOR encoded examples and the plain text
that would be extracted from them. The first example is an unsigned
integer, while the second is a byte string.
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CBOR Plain Text Extraction Examples
+==============================+=======+==========================+
| CBOR Encoding (Hex) | CBOR | Plain Text Part (Hex) |
| | Part | |
| | (Hex) | |
+==============================+=======+==========================+
| 18ED | 18 | ED |
+------------------------------+-------+--------------------------+
| C24CDEADBEEFDEADBEEFDEADBEEF | C24C | DEADBEEFDEADBEEFDEADBEEF |
+------------------------------+-------+--------------------------+
Table 7
Similarly, the cipher text used during decryption MUST be calculated
as the single, definite-length CBOR byte string representing the
block-type-specific data field excluding the CBOR byte string
identifying byte and optional CBOR byte string length field.
All other fields of the security target (such as the block type code,
block number, block processing control flags, or any CRC information)
MUST NOT be considered as part of encryption or decryption.
4.7.2. Additional Authenticated Data
The construction of additional authenticated data depends on the AAD
scope flags that can be provided as part of customizing the behavior
of this security context.
The canonical form of the AAD input to the BCB-AES-GCM mechanism is
constructed using the following process. While the AAD scope flags
might not be included in the BCB representing the security operation,
they MUST be included in the AAD value itself. This process MUST be
followed when generating AAD for either encryption or decryption.
1. The canonical form of the AAD starts as the CBOR encoding of the
AAD scope flags in which all unset flags, reserved bits, and
unassigned bits have been set to 0. For example, if the primary
block flag, target header flag, and security header flag are each
set, then the initial value of the canonical form of the AAD will
be 0x07.
2. If the primary block flag of the AAD scope flags is set to 1,
then a canonical form of the bundle's primary block MUST be
calculated and the result appended to the AAD.
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3. If the target header flag of the AAD scope flags is set to 1,
then the canonical form of the block type code, block number, and
block processing control flags associated with the security
target MUST be calculated and, in that order, appended to the
AAD.
4. If the security header flag of the AAD scope flags is set to 1,
then the canonical form of the block type code, block number, and
block processing control flags associated with the BIB MUST be
calculated and, in that order, appended to the AAD.
4.8. Processing
4.8.1. Encryption
During encryption, four inputs are prepared for input to the AES/GCM
cipher: the encryption key, the IV, the security target plain text to
be encrypted, and any additional authenticated data. These data
items MUST be generated as follows.
Prior to encryption, if a CRC value is present for the target block,
then that CRC value MUST be removed. This requires removing the CRC
field from the target block and setting the CRC type field of the
target block to "no CRC is present."
The encryption key MUST have the appropriate length as required by
local security policy. The key might be generated specifically
for this encryption, given as part of local security policy, or
through some other key management mechanism as discussed in
Section 4.5.
The IV selected MUST be of the appropriate length. Because
replaying an IV in counter mode voids the confidentiality of all
messages encrypted with said IV, this context also requires a
unique IV for every encryption performed with the same key. This
means the same key and IV combination MUST NOT be used more than
once.
The security target plain text for encryption MUST be generated as
discussed in Section 4.7.1.
Additional authenticated data MUST be generated as discussed in
Section 4.7.2 with the value of AAD scope flags being taken from
local security policy.
Upon successful encryption the following actions MUST occur.
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The cipher text produced by AES/GCM MUST replace the bytes used to
define the plain text in the security target block's block-type-
specific data field. The block length of the security target MUST
be updated if the generated cipher text is larger than the plain
text (which can occur when the authentication tag is included in
the cipher text calculation, as discussed in Section 4.4).
The authentication tag calculated by the AES/GCM cipher MAY be
added as a security result for the security target in the BCB
holding results for this security operation, in which case it MUST
be processed as described in Section 4.4.
The authentication tag MUST be included either as a security
result in the BCB representing the security operation or (with the
cipher text) in the security target block-type-specific data
field.
Finally, the BCB containing information about this security operation
MUST be updated as follows. These operations can occur in any order.
The security context identifier for the BCB MUST be set to the
context identifier for BCB-AES-GCM.
The IV input to the cipher MUST be added as the IV security
parameter for the BCB.
Any local flags used to generated AAD for this cipher MUST be
placed in the AAD scope flags security parameter for the BCB
unless these flags are expected to be correctly configured at
security verifiers and security acceptors in the network.
The encryption key MAY be included as a security parameter in
which case it MUST be wrapped using the NIST AES-KW algorithm and
the results of the wrapping added as the wrapped key security
parameter for the BCB.
The AES variant used by this security context SHOULD be added as
the AES variant security parameter for the BCB if it differs from
the default key length. Otherwise, this parameter MAY be omitted
if doing so provides a useful reduction in message sizes.
Problems encountered in the encryption MUST be processed in
accordance with local security policy. This MAY include restoring a
CRC value removed from the target block prior to encryption, if the
target block is allowed to be transmitted after an encryption error.
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4.8.2. Decryption
During decryption, five inputs are prepared for input to the AES/GCM
cipher: the decryption key, the IV, the security target cipher text
to be decrypted, any additional authenticated data, and the
authentication tag generated from the original encryption. These
data items MUST be generated as follows.
The decryption key MUST be derived using the wrapped key security
parameter if such a parameter is included in the security context
parameters of the BCB. Otherwise this key MUST be derived in
accordance with local security policy at the decrypting node as
discussed in Section 4.5.
The IV MUST be set to the value of the IV security parameter
included in the BCB. If the IV parameter is not included as a
security parameter, an IV MAY be derived as a function of local
security policy and other BCB contents or a lack of an IV security
parameter in the BCB MAY be treated as an error by the decrypting
node.
The security target cipher text for decryption MUST be generated
as discussed in Section 4.7.1.
Additional authenticated data MUST be generated as discussed in
Section 4.7.2 with the value of AAD scope flags being taken from
the AAD scope flags security context parameter. If the AAD scope
flags parameter is not included in the security context parameters
then these flags MAY be derived from local security policy in
cases where the set of such flags is determinable in the network.
The authentication tag MUST be present either as a security result
in the BCB representing the security operation or (with the cipher
text) in the security target block-type-specific data field.
Upon successful decryption the following actions MUST occur.
The plain text produced by AES/GCM MUST replace the bytes used to
define the cipher text in the security target block's block-type-
specific data field. Any changes to the security target block
length field MUST be corrected in cases where the plain text has a
different length than the replaced cipher text.
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If the security acceptor is not the bundle destination and if no
other integrity or confidentiality service is being applied to the
target block, then a CRC MUST be included for the target block. The
CRC type, as determined by policy, is set in the target block's CRC
type field and the corresponding CRC value is added as the CRC field
for that block.
If the cipher text fails to authenticate, if any needed parameters
are missing, or if there are other problems in the decryption then
the decryption MUST be treated as failed and processed in accordance
with local security policy.
5. IANA Considerations
5.1. Security Context Identifiers
This specification allocates two security context identifiers from
the "BPSec Security Context Identifiers" registry defined in
[I-D.ietf-dtn-bpsec].
Additional Entries for the BPSec Security Context Identifiers
Registry:
+=======+===============+===============+
| Value | Description | Reference |
+=======+===============+===============+
| TBA | BIB-HMAC-SHA2 | This document |
+-------+---------------+---------------+
| TBA | BCB-AES-GCM | This document |
+-------+---------------+---------------+
Table 8
5.2. Integrity Scope Flags
The BIB-HMAC-SHA2 security context has an Integrity Scope Flags field
for which IANA is requested to create and maintain a new registry
named "BPSec BIB-HMAC-SHA2 Integrity Scope Flags" on the Bundle
Protocol registry page. Initial values for this registry are given
below.
The registration policy for this registry is: Specification Required.
The value range is unsigned 16-bit integer.
BPSec BIB-HMAC-SHA2 Integrity Scope Flags Registry
+==============================+=======================+===========+
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| Bit Position (right to left) | Description | Reference |
+==============================+=======================+===========+
| 0 | Include primary block | This |
| | | document |
+------------------------------+-----------------------+-----------+
| 1 | Include target header | This |
| | flag | document |
+------------------------------+-----------------------+-----------+
| 2 | Include security | This |
| | header flag | document |
+------------------------------+-----------------------+-----------+
| 3-7 | reserved | This |
| | | document |
+------------------------------+-----------------------+-----------+
| 8-15 | unassigned | This |
| | | document |
+------------------------------+-----------------------+-----------+
Table 9
5.3. AAD Scope Flags
The BCB-AES-GCM security context has an AAD Scope Flags field for
which IANA is requested to create and maintain a new registry named
"BPSec BCB-AES-GCM AAD Scope Flags" on the Bundle Protocol registry
page. Initial values for this registry are given below.
The registration policy for this registry is: Specification Required.
The value range is unsigned 16-bit integer.
BPSec BCB-AES-GCM AAD Scope Flags Registry
+==============================+=======================+===========+
| Bit Position (right to left) | Description | Reference |
+==============================+=======================+===========+
| 0 | Include primary block | This |
| | | document |
+------------------------------+-----------------------+-----------+
| 1 | Include target header | This |
| | flag | document |
+------------------------------+-----------------------+-----------+
| 2 | Include security | This |
| | header flag | document |
+------------------------------+-----------------------+-----------+
| 3-7 | reserved | This |
| | | document |
+------------------------------+-----------------------+-----------+
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| 8-15 | unassigned | This |
| | | document |
+------------------------------+-----------------------+-----------+
Table 10
5.4. Guidance for Designated Experts
New assignments within the BIB-HMAC-SHA2 Integrity Scope Flags
Registry and the BCB-AES-GCM AAD Scope Flags Registry require review
by a Designated Expert (DE). This section provides guidance to the
DE when performing their reviews. Specifically, a DE is expected to
perform the following activities.
* Ascertain the existence of suitable documentation (a
specification) as described in [RFC8126] and to verify that the
document is permanently and publicly available.
* Ensure that any changes to the Integrity Scope Flags clearly state
how new assignments interact with existing flags and how the
inclusion of new assignments affects the construction of the IPPT
value.
* Ensure that any changes to the AAD Scope Flags clearly state how
new assignments interact with existing flags and how the inclusion
of new assignments affects the construction of the AAD input to
the BCB-AES-GCM mechanism.
* Ensure that any processing changes proposed with new assignments
do not alter any required behavior in this specification.
6. Security Considerations
Security considerations specific to a single security context are
provided in the description of that context. This section discusses
security considerations that should be evaluated by implementers of
any security context described in this document. Considerations can
also be found in documents listed as normative references and they
should also be reviewed by security context implementors.
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6.1. Key Management
The delayed and disrupted nature of DTNs complicates the process of
key management because there might not be reliable, timely round-trip
exchange between security sources, security verifiers, and security
acceptors in the network. This is true when there is a substantial
signal propagation delay between nodes, when nodes are in a highly
challenged communications environment, and when nodes do not support
bi-directional communication.
In these environments, key establishment protocols that rely on
round-trip information exchange might not converge on a shared secret
in a timely manner (or at all). Also, key revocation or key
verification mechanisms that rely on access to a centralized
authority (such as a certificate authority) might similarly fail in
the stressing conditions of a DTN.
For these reasons, the default security contexts described in this
document rely on symmetric key cryptographic mechanisms because
asymmetric key infrastructure (such as a public key infrastructure)
might be impractical in this environment.
BPSec assumes that "key management is handled as a separate part of
network management" [I-D.ietf-dtn-bpsec]. This assumption is also
made by the security contexts defined in this document which do not
define new protocols for key derivation, exchange of key-encrypting
keys, revocation of existing keys, or the security configuration or
policy used to select certain keys for certain security operations.
Nodes using these security contexts need to perform the following
kinds of activities, independent of the construction, transmission,
and processing of BPSec security blocks.
Establish shared key-encrypting-keys with other nodes in the
network using an out-of-band mechanism. This might include pre-
sharing of key encryption keys or the use of traditional key
establishment mechanisms prior to the exchange of BPsec security
blocks.
Determine when a key is considered exhausted and no longer to be
used in the generation, verification, or acceptance of a security
block.
Determine when a key is considered invalid and no longer to be
used in the generation, verification, or acceptance of a security
block. Such revocations can be based on a variety of mechanisms
to include local security policy, time relative to the generation
or use of the key, or as specified through network management.
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Determine, through an out-of-band mechanism such as local security
policy, what keys are to be used for what security blocks. This
includes the selection of which key should be used in the
evaluation of a security block received by a security verifier or
a security acceptor.
The failure to provide effective key management techniques
appropriate for the operational networking environment can result in
the compromise of those unmanaged keys and the loss of security
services in the network.
6.2. Key Handling
Once generated, keys should be handled as follows.
It is strongly RECOMMENDED that implementations protect keys both
when they are stored and when they are transmitted.
In the event that a key is compromised, any security operations
using a security context associated with that key SHOULD also be
considered compromised. This means that the BIB-HMAC-SHA2
security context SHOULD NOT be treated as providing integrity when
used with a compromised key and BCB-AES-GCM SHOULD NOT be treated
as providing confidentiality when used with a compromised key.
The same key, whether a key-encrypting-key or a wrapped key, MUST
NOT be used for different algorithms as doing so might leak
information about the key.
A key-encrypting-key MUST NOT be used to encrypt keys for
different security contexts. Any key-encrypting-key used by a
security context defined in this document MUST only be used to
wrap keys associated with security operations using that security
context. This means that a compliant security source would not
use the same key-encrypting-key to wrap keys for both the BIB-
HMAC-SHA2 and BCB-AES-GCM security contexts. Similarly, any
compliant security verifier or security acceptor would not use the
same key-encrypting-key to unwrap keys for different security
contexts.
6.3. AES GCM
There are a significant number of considerations related to the use
of the GCM mode of AES to provide a confidentiality service. These
considerations are provided in Section 4.6 as part of the
documentation of the BCB-AES-GCM security context.
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The length of the cipher text produced by the GCM mode of AES will be
equal to the length of the plain text input to the cipher suite. The
authentication tag also produced by this cipher suite is separate
from the cipher text. However, it should be noted that
implementations of the AES-GCM cipher suite might not separate the
concept of cipher text and authentication tag in their application
programming interface (API).
Implementations of the BCB-AES-GCM security context can either keep
the length of the target block unchanged by holding the
authentication tag in a BCB security result or alter the length of
the target block by including the authentication tag with the cipher
text replacing the block-type-specific-data field of the target
block. Implementations MAY use the authentication tag security
result in cases where keeping target block length unchanged is an
important processing concern. In all cases, the cipher text and
authentication tag MUST be processed in accordance with the API of
the AES-GCM cipher suites at the security source and security
acceptor.
6.4. AES Key Wrap
The AES key wrap (AES-KW) algorithm used by the security contexts in
this document does not use a per-invocation initialization vector and
does not require any key padding. Key padding is not needed because
wrapped keys used by these security contexts will always be multiples
of 8 bytes. The length of the wrapped key can be determined by
inspecting the security context parameters. Therefore, a key can be
unwrapped using only the information present in the security block
and the key encryption key provided by local security policy at the
security verifier or security acceptor.
6.5. Bundle Fragmentation
Bundle fragmentation might prevent security services in a bundle from
being verified after a bundle is fragmented and before the bundle is
re-assembled. Examples of potential issues include the following.
If a security block and its security target do not exist in the
same fragment, then the security block cannot be processed until
the bundle is re-assembled. If a fragment includes an encrypted
target block, but not its BCB, then a receiving bundle processing
agent (BPA) will not know that the target block has been
encrypted.
A security block can be cryptographically bound to a bundle by
setting the Integrity Scope Flags (for BIB-HMAC-SHA2) or the AAD
Scope Flags (for BCB-AES-GCM) to include the bundle primary block.
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When a security block is cryptographically bound to a bundle, it
cannot be processed even if the security block and target both
coexist in the fragment. This is because fragments have different
primary blocks than the original bundle.
If security blocks and their target blocks are repeated in
multiple fragments, policy needs to determine how to deal with
issues where a security operation verifies in one fragment but
fails in another fragment. This might happen, for example, if a
BIB block becomes corrupted in one fragment but not in another
fragment.
Implementors should consider how security blocks are processed when a
BPA fragments a received bundle. For example, security blocks and
their targets could be placed in the same fragment if the security
block is not otherwise cryptographically bound to the bundle being
fragmented. Alternatively, if security blocks are cryptographically
bound to a bundle, then a fragmenting BPA should consider
encapsulating the bundle first and then fragmenting the encapsulating
bundle.
7. Normative References
[AES-GCM] Dworkin, M., "NIST Special Publication 800-38D:
Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC.", November 2007.
[I-D.ietf-dtn-bpbis]
Burleigh, S., Fall, K., and E. J. Birrane, "Bundle
Protocol Version 7", Work in Progress, Internet-Draft,
draft-ietf-dtn-bpbis-31, 25 January 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-dtn-
bpbis-31>.
[I-D.ietf-dtn-bpsec]
III, E. J. B. and K. McKeever, "Bundle Protocol Security
Specification", Work in Progress, Internet-Draft, draft-
ietf-dtn-bpsec-27, 16 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-dtn-
bpsec-27>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5649] Housley, R. and M. Dworkin, "Advanced Encryption Standard
(AES) Key Wrap with Padding Algorithm", RFC 5649,
DOI 10.17487/RFC5649, September 2009,
<https://www.rfc-editor.org/info/rfc5649>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[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>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
[SHS] US NIST, "Secure Hash Standard (SHS).", FIPS-
180-4, Gaithersburg, MD, USA, August 2015.
https://csrc.nist.gov/publications/detail/fips/180/4/final
Appendix A. Examples
This appendix is informative.
This section presents a series of examples of constructing BPSec
security blocks (using the security contexts defined in this
document) and adding those blocks to a sample bundle.
The examples presented in this appendix represent valid constructions
of bundles, security blocks, and the encoding of security context
parameters and results. For this reason, they can inform unit test
suites for individual implementations as well as interoperability
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test suites amongst implementations. However, these examples do not
cover every permutation of security parameters, security results, or
use of security blocks in a bundle.
NOTE: The bundle diagrams in this section are patterned after the
bundle diagrams used in [I-D.ietf-dtn-bpsec] Section 3.11 "BSP Block
Examples".
NOTE: Figures in this section identified as "(CBOR Diagnostic
Notation)" are represented using the CBOR diagnostic notation defined
in [RFC8949]. This notation is used to express CBOR data structures
in a manner that enables visual inspection. The bundles, security
blocks, and security context contents in these figures are
represented using CBOR structures. In cases where BP blocks (to
include BPSec security blocks) are comprised of a sequence of CBOR
objects, these objects are represented as a CBOR sequence as defined
in [RFC8742].
NOTE: Examples in this section use the "ipn" URI scheme for
EndpointID naming, as defined in [I-D.ietf-dtn-bpbis].
NOTE: The bundle source is presumed to be the security source for all
security blocks in this section, unless otherwise noted.
A.1. Example 1: Simple Integrity
This example shows the addition of a BIB to a sample bundle to
provide integrity for the payload block.
A.1.1. Original Bundle
The following diagram shows the original bundle before the BIB has
been added.
Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Payload Block | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 1: Example 1 Original Bundle
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A.1.1.1. Primary Block
The BPv7 bundle has no special processing flags and no CRC is
provided because the primary block is expected to be protected by an
integrity service BIB using the BIB-HMAC-SHA2 security context.
The bundle is sourced at the source node ipn:2.1 and destined for the
destination node ipn:1.2. The bundle creation time uses a DTN
creation time of 0 indicating lack of an accurate clock and a
sequence number of 40. The lifetime of the bundle is given as
1,000,000 milliseconds since the bundle creation time.
The primary block is provided as follows.
[
7, / BP version /
0, / flags /
0, / CRC type /
[2, [1,2]], / destination (ipn:1.2) /
[2, [2,1]], / source (ipn:2.1) /
[2, [2,1]], / report-to (ipn:2.1) /
[0, 40], / timestamp /
1000000 / lifetime /
]
Figure 2: Primary Block (CBOR Diagnostic Notation)
The CBOR encoding of the primary block is
0x88070000820282010282028202018202820201820018281a000f4240.
A.1.1.2. Payload Block
Other than its use as a source of plaintext for security blocks, the
payload has no required distinguishing characteristic for the purpose
of this example. The sample payload is a 32 byte string whose value
is "Ready Generate a 32 byte payload".
The payload is represented in the payload block as a byte string of
the raw payload string. It is NOT represented as a CBOR text string
wrapped within a CBOR binary string. The hex value of the payload
"Ready Generate a 32 byte payload" is
0x52656164792047656e657261746520612033322062797465207061796c6f6164.
The payload block is provided as follows.
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[
1, / type code: Payload block /
1, / block number /
0, / block processing flags /
0, / CRC Type /
h'52656164792047656e65726174652061 / type-specific-data: payload /
2033322062797465207061796c6f6164'
]
Figure 3: Payload Block (CBOR Diagnostic Notation)
The CBOR encoding of the payload block is 0x8501010000582052656164792
047656e657261746520612033322062797465207061796c6f6164.
A.1.1.3. Bundle CBOR Representation
A BPv7 bundle is represented as an indefinite-length array consisting
of the blocks comprising the bundle, with a terminator character at
the end.
The CBOR encoding of the original bundle is 0x9f880700008202820102820
28202018202820201820018281a000f42408501010000582052656164792047656e65
7261746520612033322062797465207061796c6f6164ff.
A.1.2. Security Operation Overview
This example adds a BIB to the bundle using the BIB-HMAC-SHA2
security context to provide an integrity mechanism over the payload
block.
The following diagram shows the resulting bundle after the BIB is
added.
Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Bundle Integrity Block | 11 | 2 |
| OP(bib-integrity, target=1) | | |
+----------------------------------------+-------+--------+
| Payload Block | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 4: Example 1 Resulting Bundle
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A.1.3. Bundle Integrity Block
In this example, a BIB is used to carry an integrity signature over
the payload block.
A.1.3.1. Configuration, Parameters, and Results
For this example, the following configuration and security parameters
are used to generate the security results indicated.
This BIB has a single target and includes a single security result:
the calculated signature over the payload block.
Key : h'1a2b1a2b1a2b1a2b1a2b1a2b1a2b1a2b'
SHA Variant : HMAC 512/512
Scope Flags : 0x00
Payload Data: h'52656164792047656e65726174652061
2033322062797465207061796c6f6164'
Signature : h'0654d65992803252210e377d66d0a8dc
18a1e8a392269125ae9ac198a9a598be
4b83d5daa8be2f2d16769ec1c30cfc34
8e2205fba4b3be2b219074fdd5ea8ef0'
Figure 5: Example 1: Configuration, Parameters, and Results
A.1.3.2. Abstract Security Block
The abstract security block structure of the BIB's block-type-
specific-data field for this application is as follows.
[1], / Security Target - Payload block /
1, / Security Context ID - BIB-HMAC-SHA2 /
1, / Security Context Flags - Parameters Present /
[2,[2, 1]], / Security Source - ipn:2.1 /
[ / Security Parameters - 2 Parameters /
[1, 7], / SHA Variant - HMAC 512/512 /
[3, 0x00] / Scope Flags - No Additional Scope /
],
[ / Security Results: 1 Result /
[1, h'0654d65992803252210e377d66d0a8dc18a1e8a392269125ae9ac198a9a598b
e4b83d5daa8be2f2d16769ec1c30cfc348e2205fba4b3be2b219074fdd5ea8ef0']
]
Figure 6: Example 1: BIB Abstract Security Block (CBOR Diagnostic
Notation)
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The CBOR encoding of the BIB block-type-specific-data field (the
abstract security block) is 0x810101018202820201828201078203008182015
8400654d65992803252210e377d66d0a8dc18a1e8a392269125ae9ac198a9a598be4b
83d5daa8be2f2d16769ec1c30cfc348e2205fba4b3be2b219074fdd5ea8ef0.
A.1.3.3. Representations
The BIB wrapping this abstract security block is as follows.
[
11, / type code /
2, / block number /
0, / flags /
0, / CRC type /
h'8101010182028202018282010782030081820158400654d65992803252210e377d66
d0a8dc18a1e8a392269125ae9ac198a9a598be4b83d5daa8be2f2d16769ec1c30cfc34
8e2205fba4b3be2b219074fdd5ea8ef0',
]
Figure 7: Example 1: BIB (CBOR Diagnostic Notation)
The CBOR encoding of the BIB block is 0x850b0200005855810101018202820
2018282010782030081820158400654d65992803252210e377d66d0a8dc18a1e8a392
269125ae9ac198a9a598be4b83d5daa8be2f2d16769ec1c30cfc348e2205fba4b3be2
b219074fdd5ea8ef0.
A.1.4. Final Bundle
The CBOR encoding of the full output bundle, with the BIB: 0x9f880700
00820282010282028202018202820201820018281a000f4240850b020000585581010
10182028202018282010782030081820158400654d65992803252210e377d66d0a8dc
18a1e8a392269125ae9ac198a9a598be4b83d5daa8be2f2d16769ec1c30cfc348e220
5fba4b3be2b219074fdd5ea8ef08501010000582052656164792047656e6572617465
20612033322062797465207061796c6f6164ff.
A.2. Example 2: Simple Confidentiality with Key Wrap
This example shows the addition of a BCB to a sample bundle to
provide confidentiality for the payload block. AES key wrap is used
to transmit the symmetric key used to generate the security results
for this service.
A.2.1. Original Bundle
The following diagram shows the original bundle before the BCB has
been added.
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Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Payload Block | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 8: Example 2 Original Bundle
A.2.1.1. Primary Block
The primary block used in this example is identical to the primary
block presented in Example 1 Appendix A.1.1.1.
In summary, the CBOR encoding of the primary block is
0x88070000820282010282028202018202820201820018281a000f4240.
A.2.1.2. Payload Block
The payload block used in this example is identical to the payload
block presented in Example 1 Appendix A.1.1.2.
In summary, the CBOR encoding of the payload block is 0x8501010000582
052656164792047656e657261746520612033322062797465207061796c6f6164.
A.2.1.3. Bundle CBOR Representation
A BPv7 bundle is represented as an indefinite-length array consisting
of the blocks comprising the bundle, with a terminator character at
the end.
The CBOR encoding of the original bundle is 0x9f880700008202820102820
28202018202820201820018281a000f42408501010000582052656164792047656e65
7261746520612033322062797465207061796c6f6164ff.
A.2.2. Security Operation Overview
This example adds a BCB using the BCB-AES-GCM security context using
AES key wrap to provide a confidentiality mechanism over the payload
block and transmit the symmetric key.
The following diagram shows the resulting bundle after the BCB is
added.
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Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Bundle Confidentiality Block | 12 | 2 |
| OP(bcb-confidentiality, target=1) | | |
+----------------------------------------+-------+--------+
| Payload Block (Encrypted) | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 9: Example 2 Resulting Bundle
A.2.3. Bundle Confidentiality Block
In this example, a BCB is used to encrypt the payload block and uses
AES key wrap to transmit the symmetric key.
A.2.3.1. Configuration, Parameters, and Results
For this example, the following configuration and security parameters
are used to generate the security results indicated.
This BCB has a single target, the payload block. Three security
results are generated: cipher text which replaces the plain text
block-type-specific data to encrypt the payload block, an
authentication tag, and the AES wrapped key.
Content Encryption
Key: h'71776572747975696f70617364666768'
Key Encryption Key: h'6162636465666768696a6b6c6d6e6f70'
IV: h'5477656c7665313231323132'
AES Variant: A128GCM
AES Wrapped Key: h'69c411276fecddc4780df42c8a2af892
96fabf34d7fae700'
Scope Flags: 0x00
Payload Data: h'52656164792047656e65726174652061
2033322062797465207061796c6f6164'
Authentication Tag: h'da08f4d8936024ad7c6b3b800e73dd97'
Payload Ciphertext: h'3a09c1e63fe2097528a78b7c12943354
a563e32648b700c2784e26a990d91f9d'
Figure 10: Example 2: Configuration, Parameters, and Results
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A.2.3.2. Abstract Security Block
The abstract security block structure of the BCB's block-type-
specific-data field for this application is as follows.
[1], / Security Target - Payload block /
2, / Security Context ID - BCB-AES-GCM /
1, / Security Context Flags - Parameters Present /
[2,[2, 1]], / Security Source - ipn:2.1 /
[ / Security Parameters - 4 Parameters /
[1, h'5477656c7665313231323132'], / Initialization Vector /
[2, 1], / AES Variant - A128GCM /
[3, h'69c411276fecddc4780df42c8a / AES wrapped key /
2af89296fabf34d7fae700'],
[4, 0x00] / Scope Flags - No extra scope/
],
[ / Security Results: 1 Result /
[1, h'da08f4d8936024ad7c6b3b800e73dd97'] / Payload Auth. Tag /
]
Figure 11: Example 2: BCB Abstract Security Block (CBOR
Diagnostic Notation)
The CBOR encoding of the BCB block-type-specific-data field (the
abstract security block) is 0x8101020182028202018482014c5477656c76653
132313231328202018203581869c411276fecddc4780df42c8a2af89296fabf34d7fa
e70082040081820150da08f4d8936024ad7c6b3b800e73dd97.
A.2.3.3. Representations
The BCB wrapping this abstract security block is as follows.
[
12, / type code /
2, / block number /
1, / flags - block must be replicated in every fragment /
0, / CRC type /
h'8101020182028202018482014c5477656c766531323132313282020182035818
69c411276fecddc4780df42c8a2af89296fabf34d7fae70082040081820150da
08f4d8936024ad7c6b3b800e73dd97'
]
Figure 12: Example 2: BCB (CBOR Diagnostic Notation)
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The CBOR encoding of the BCB block is 0x850c020100584f810102018202820
2018482014c5477656c76653132313231328202018203581869c411276fecddc4780d
f42c8a2af89296fabf34d7fae70082040081820150da08f4d8936024ad7c6b3b800e7
3dd97.
A.2.4. Final Bundle
The CBOR encoding of the full output bundle, with the BCB: 0x9f880700
00820282010282028202018202820201820018281a000f4240850c020100584f81010
20182028202018482014c5477656c76653132313231328202018203581869c411276f
ecddc4780df42c8a2af89296fabf34d7fae70082040081820150da08f4d8936024ad7
c6b3b800e73dd97850101000058203a09c1e63fe2097528a78b7c12943354a563e326
48b700c2784e26a990d91f9dff.
A.3. Example 3: Security Blocks from Multiple Sources
This example shows the addition of a BIB and BCB to a sample bundle.
These two security blocks are added by two different nodes. The BCB
is added by the source endpoint and the BIB is added by a forwarding
node.
The resulting bundle contains a BCB to encrypt the Payload Block and
a BIB to provide integrity to the Primary and Bundle Age Block.
A.3.1. Original Bundle
The following diagram shows the original bundle before the security
blocks have been added.
Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Extension Block: Bundle Age Block | 7 | 2 |
+----------------------------------------+-------+--------+
| Payload Block | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 13: Example 3 Original Bundle
A.3.1.1. Primary Block
The primary block used in this example is identical to the primary
block presented in Example 1 Appendix A.1.1.1.
In summary, the CBOR encoding of the primary block is
0x88070000820282010282028202018202820201820018281a000f4240.
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A.3.1.2. Bundle Age Block
A bundle age block is added to the bundle to help other nodes in the
network determine the age of the bundle. The use of this block is as
recommended because the bundle source does not have an accurate clock
(as indicated by the DTN time of 0).
Because this block is specified at the time the bundle is being
forwarded, the bundle age represents the time that has elapsed from
the time the bundle was created to the time it is being prepared for
forwarding. In this case, the value is given as 300 milliseconds.
The bundle age extension block is provided as follows.
[
7, / type code: Bundle Age block /
2, / block number /
0, / block processing flags /
0, / CRC Type /
<<300>> / type-specific-data: age /
]
Figure 14: Bundle Age Block (CBOR Diagnostic Notation)
The CBOR encoding of the bundle age block is 0x85070200004319012c.
A.3.1.3. Payload Block
The payload block used in this example is identical to the payload
block presented in Example 1 Appendix A.1.1.2.
In summary, the CBOR encoding of the payload block is 0x8501010000582
052656164792047656e657261746520612033322062797465207061796c6f6164.
A.3.1.4. Bundle CBOR Representation
A BPv7 bundle is represented as an indefinite-length array consisting
of the blocks comprising the bundle, with a terminator character at
the end.
The CBOR encoding of the original bundle is 0x9f880700008202820102820
28202018202820201820018281a000f424085070200004319012c8501010000582052
656164792047656e657261746520612033322062797465207061796c6f6164ff.
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A.3.2. Security Operation Overview
This example provides:
a BIB with the BIB-HMAC-SHA2 security context to provide an
integrity mechanism over the primary block and bundle age block.
a BCB with the BCB-AES-GCM security context to provide a
confidentiality mechanism over the payload block.
The following diagram shows the resulting bundle after the security
blocks are added.
Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Bundle Integrity Block | 11 | 3 |
| OP(bib-integrity, targets=0, 2) | | |
+----------------------------------------+-------+--------+
| Bundle Confidentiality Block | 12 | 4 |
| OP(bcb-confidentiality, target=1) | | |
+----------------------------------------+-------+--------+
| Extension Block: Bundle Age Block | 7 | 2 |
+----------------------------------------+-------+--------+
| Payload Block (Encrypted) | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 15: Example 3 Resulting Bundle
A.3.3. Bundle Integrity Block
In this example, a BIB is used to carry an integrity signature over
the bundle age block and an additional signature over the payload
block. The BIB is added by a waypoint node, ipn:3.0.
A.3.3.1. Configuration, Parameters, and Results
For this example, the following configuration and security parameters
are used to generate the security results indicated.
This BIB has two security targets and includes two security results,
holding the calculated signatures over the bundle age block and
primary block.
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Key: h'1a2b1a2b1a2b1a2b1a2b1a2b1a2b1a2b'
SHA Variant: HMAC 256/256
Scope Flags: 0x00
Primary Block Data: h'88070000820282010282028202018202
820201820018281a000f4240'
Bundle Age Block
Data: h'85070200004319012c'
Primary Block
Signature: h'8e059b8e71f7218264185a666bf3e453
076f2b883f4dce9b3cdb6464ed0dcf0f'
Bundle Age Block
Signature: h'72dee8eba049a22978e84a95d0496466
8eb131b1ca4800c114206d70d9065c80'
Figure 16: Example 3: Configuration, Parameters, and Results for
the BIB
A.3.3.2. Abstract Security Block
The abstract security block structure of the BIB's block-type-
specific-data field for this application is as follows.
[0, 2], / Security Targets /
1, / Security Context ID - BIB-HMAC-SHA2 /
1, / Security Context Flags - Parameters Present /
[2,[3, 0]], / Security Source - ipn:3.0 /
[ / Security Parameters - 2 Parameters /
[1, 5], / SHA Variant - HMAC 256/256 /
[3, 0x00] / Scope Flags - No Additional Scope /
],
[ / Security Results: 2 Results /
[1, h'8e059b8e71f7218264185a666bf3e453
076f2b883f4dce9b3cdb6464ed0dcf0f'], / Primary Block /
[1, h'72dee8eba049a22978e84a95d0496466
8eb131b1ca4800c114206d70d9065c80'] / Bundle Age Block /
]
Figure 17: Example 3: BIB Abstract Security Block (CBOR
Diagnostic Notation)
The CBOR encoding of the BIB block-type-specific-data field (the
abstract security block) is 0x820002010182028203008282010582030082820
158208e059b8e71f7218264185a666bf3e453076f2b883f4dce9b3cdb6464ed0dcf0f
8201582072dee8eba049a22978e84a95d04964668eb131b1ca4800c114206d70d9065
c80.
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A.3.3.3. Representations
The BIB wrapping this abstract security block is as follows.
[
11, / type code /
3, / block number /
0, / flags /
0, / CRC type /
h'820002010182028203008282010582030082820158208e059b8e71f721826418
5a666bf3e453076f2b883f4dce9b3cdb6464ed0dcf0f8201582072dee8eba049
a22978e84a95d04964668eb131b1ca4800c114206d70d9065c80',
]
Figure 18: Example 3: BIB (CBOR Diagnostic Notation)
The CBOR encoding of the BIB block is 0x850b030000585a820002010182028
203008282010582030082820158208e059b8e71f7218264185a666bf3e453076f2b88
3f4dce9b3cdb6464ed0dcf0f8201582072dee8eba049a22978e84a95d04964668eb13
1b1ca4800c114206d70d9065c80.
A.3.4. Bundle Confidentiality Block
In this example, a BCB is used encrypt the payload block. The BCB is
added by the bundle source node, ipn:2.1.
A.3.4.1. Configuration, Parameters, and Results
For this example, the following configuration and security parameters
are used to generate the security results indicated.
This BCB has a single target, the payload block. Two security
results are generated: cipher text which replaces the plain text
block-type-specific data to encrypt the payload block, and an
authentication tag.
Content Encryption
Key: h'71776572747975696f70617364666768'
IV: h'5477656c7665313231323132'
AES Variant: A128GCM
Scope Flags: 0x00
Payload Data: h'52656164792047656e65726174652061
2033322062797465207061796c6f6164'
Authentication Tag: h'da08f4d8936024ad7c6b3b800e73dd97'
Payload Ciphertext: h'3a09c1e63fe2097528a78b7c12943354
a563e32648b700c2784e26a990d91f9d'
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Figure 19: Example 3: Configuration, Parameters, and Results for
the BCB
A.3.4.2. Abstract Security Block
The abstract security block structure of the BCB's block-type-
specific-data field for this application is as follows.
[1], / Security Target - Payload block /
2, / Security Context ID - BCB-AES-GCM /
1, / Security Context Flags - Parameters Present /
[2,[2, 1]], / Security Source - ipn:2.1 /
[ / Security Parameters - 3 Parameters /
[1, h'5477656c7665313231323132'], / Initialization Vector /
[2, 1], / AES Variant - AES 128 /
[4, 0x00] / Scope Flags - No Additional Scope /
],
[ / Security Results: 1 Result /
[1, h'da08f4d8936024ad7c6b3b800e73dd97'] / Payload Auth. Tag /
]
Figure 20: Example 3: BCB Abstract Security Block (CBOR
Diagnostic Notation)
The CBOR encoding of the BCB block-type-specific-data field (the
abstract security block) is 0x8101020182028202018382014c5477656c76653
1323132313282020182040081820150da08f4d8936024ad7c6b3b800e73dd97.
A.3.4.3. Representations
The BCB wrapping this abstract security block is as follows.
[
12, / type code /
4, / block number /
1, / flags - block must be replicated in every fragment /
0, / CRC type /
h'8101020182028202018382014c5477656c766531323132313282020182040081
820150da08f4d8936024ad7c6b3b800e73dd97',
]
Figure 21: Example 3: BCB (CBOR Diagnostic Notation)
The CBOR encoding of the BCB block is 0x850c0401005833810102018202820
2018382014c5477656c766531323132313282020182040081820150da08f4d8936024
ad7c6b3b800e73dd97.
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A.3.5. Final Bundle
The CBOR encoding of the full output bundle, with the BIB and BCB
added is: 0x9f88070000820282010282028202018202820201820018281a000f424
0850b030000585a820002010182028203008282010582030082820158208e059b8e71
f7218264185a666bf3e453076f2b883f4dce9b3cdb6464ed0dcf0f8201582072dee8e
ba049a22978e84a95d04964668eb131b1ca4800c114206d70d9065c80850c04010058
338101020182028202018382014c5477656c766531323132313282020182040081820
150da08f4d8936024ad7c6b3b800e73dd9785070200004319012c850101000058203a
09c1e63fe2097528a78b7c12943354a563e32648b700c2784e26a990d91f9dff.
A.4. Example 4: Security Blocks with Full Scope
This example shows the addition of a BIB and BCB to a sample bundle.
A BIB is added to provide integrity over the payload block and a BCB
is added for confidentiality over the payload and BIB.
The integrity scope and additional authentication data will bind the
primary block, target header, and the security header.
A.4.1. Original Bundle
The following diagram shows the original bundle before the security
blocks have been added.
Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Payload Block | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 22: Example 4 Original Bundle
A.4.1.1. Primary Block
The primary block used in this example is identical to the primary
block presented in Example 1 Appendix A.1.1.1.
In summary, the CBOR encoding of the primary block is
0x88070000820282010282028202018202820201820018281a000f4240.
A.4.1.2. Payload Block
The payload block used in this example is identical to the payload
block presented in Example 1 Appendix A.1.1.2.
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In summary, the CBOR encoding of the payload block is 0x8501010000582
052656164792047656e657261746520612033322062797465207061796c6f6164.
A.4.1.3. Bundle CBOR Representation
A BPv7 bundle is represented as an indefinite-length array consisting
of the blocks comprising the bundle, with a terminator character at
the end.
The CBOR encoding of the original bundle is 0x9f880700008202820102820
28202018202820201820018281a000f42408501010000582052656164792047656e65
7261746520612033322062797465207061796c6f6164ff.
A.4.2. Security Operation Overview
This example provides:
a BIB with the BIB-HMAC-SHA2 security context to provide an
integrity mechanism over the payload block.
a BCB with the BCB-AES-GCM security context to provide a
confidentiality mechanism over the payload block and BIB.
The following diagram shows the resulting bundle after the security
blocks are added.
Block Block Block
in Bundle Type Number
+========================================+=======+========+
| Primary Block | N/A | 0 |
+----------------------------------------+-------+--------+
| Bundle Integrity Block (Encrypted) | 11 | 3 |
| OP(bib-integrity, target=1) | | |
+----------------------------------------+-------+--------+
| Bundle Confidentiality Block | 12 | 2 |
| OP(bcb-confidentiality, targets=1, 3) | | |
+----------------------------------------+-------+--------+
| Payload Block (Encrypted) | 1 | 1 |
+----------------------------------------+-------+--------+
Figure 23: Example 4 Resulting Bundle
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A.4.3. Bundle Integrity Block
In this example, a BIB is used to carry an integrity signature over
the payload block. The IPPT contains the payload block block-type-
specific data, primary block data, the payload block header, and the
BIB header. That is, all additional headers are included in the
IPPT.
A.4.3.1. Configuration, Parameters, and Results
For this example, the following configuration and security parameters
are used to generate the security results indicated.
This BIB has a single target and includes a single security result:
the calculated signature over the Payload block.
Key: h'1a2b1a2b1a2b1a2b1a2b1a2b1a2b1a2b'
SHA Variant: HMAC 384/384
Scope Flags: 0x07 (all additional headers)
Primary Block Data: h'88070000820282010282028202018202
820201820018281a000f4240
Payload Data: h'52656164792047656e65726174652061
2033322062797465207061796c6f6164'
Payload Header: h'85010100005820'
BIB Header: h'850b0300005845'
Payload Signature: h'07c84d929f83bee4690130729d77a1bd
da9611cd6598e73d0659073ea74e8c27
523b02193cb8ba64be58dbc556887aca
Figure 24: Example 4: Configuration, Parameters, and Results for
the BIB
A.4.3.2. Abstract Security Block
The abstract security block structure of the BIB's block-type-
specific-data field for this application is as follows.
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[1], / Security Target - Payload block /
1, / Security Context ID - BIB-HMAC-SHA2 /
1, / Security Context Flags - Parameters Present /
[2,[2, 1]], / Security Source - ipn:2.1 /
[ / Security Parameters - 2 Parameters /
[1, 6], / SHA Variant - HMAC 384/384 /
[3, 0x07] / Scope Flags - All additional headers in the SHA Hash /
],
[ / Security Results: 1 Result /
[1, h'07c84d929f83bee4690130729d77a1bdda9611cd6598e73d
0659073ea74e8c27523b02193cb8ba64be58dbc556887aca']
]
Figure 25: Example 4: BIB Abstract Security Block (CBOR
Diagnostic Notation)
The CBOR encoding of the BIB block-type-specific-data field (the
abstract security block) is 0x810101018202820201828201068203078182015
83007c84d929f83bee4690130729d77a1bdda9611cd6598e73d0659073ea74e8c2752
3b02193cb8ba64be58dbc556887aca.
A.4.3.3. Representations
The BIB wrapping this abstract security block is as follows.
[
11, / type code /
3, / block number /
0, / flags /
0, / CRC type /
h'81010101820282020182820106820307818201583007c84d929f83bee4690130
729d77a1bdda9611cd6598e73d0659073ea74e8c27523b02193cb8ba64be58db
c556887aca',
]
Figure 26: Example 4: BIB (CBOR Diagnostic Notation)
The CBOR encoding of the BIB block is 0x850b0300005845810101018202820
20182820106820307818201583007c84d929f83bee4690130729d77a1bdda9611cd65
98e73d0659073ea74e8c27523b02193cb8ba64be58dbc556887aca.
A.4.4. Bundle Confidentiality Block
In this example, a BCB is used encrypt the payload block and the BIB
that provides integrity over the payload.
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A.4.4.1. Configuration, Parameters, and Results
For this example, the following configuration and security parameters
are used to generate the security results indicated.
This BCB has two targets: the payload block and BIB. Four security
results are generated: cipher text which replaces the plain text
block-type-specific data of the payload block, cipher text to encrypt
the BIB, and authentication tags for both the payload block and BIB.
Key: h'71776572747975696f70617364666768
71776572747975696f70617364666768'
IV: h'5477656c7665313231323132'
AES Variant: A256GCM
Scope Flags: 0x07 (All additional headers)
Payload Data: h'52656164792047656e65726174652061
2033322062797465207061796c6f6164'
BIB Data: h'81010101820282020182820106820307
818201583007c84d929f83bee4690130
729d77a1bdda9611cd6598e73d065907
3ea74e8c27523b02193cb8ba64be58db
c556887aca
BIB
Authentication Tag: h'c95ed4534769b046d716e1cdfd00830e'
Payload Block
Authentication Tag: h'0e365c700e4bb19c0d991faff5345aff'
Payload Ciphertext: h'90eab64575930498d6aa654107f15e96
319bb227706000abc8fcac3b9bb9c87e'
BIB Ciphertext: h'438ed6208eb1c1ffb94d952175167df0
902a815f221ebc837a134efc13bfa82a
2d5d317747da3eb54acef4ca839bd961
487284404259b60be12b8aed2f3e8a36
2836529f66'
Figure 27: Example 4: Configuration, Parameters, and Results for
the BCB
A.4.4.2. Abstract Security Block
The abstract security block structure of the BCB's block-type-
specific-data field for this application is as follows.
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[3, 1], / Security Targets /
2, / Security Context ID - BCB-AES-GCM /
1, / Security Context Flags - Parameters Present /
[2,[2, 1]], / Security Source - ipn:2.1 /
[ / Security Parameters - 3 Parameters /
[1, h'5477656c7665313231323132'], / Initialization Vector /
[2, 3], / AES Variant - AES 256 /
[4, 0x07] / Scope Flags - All headers in SHA hash /
],
[ / Security Results: 2 Results /
[1, h'c95ed4534769b046d716e1cdfd00830e'], / BIB Auth. Tag /
[1, h'0e365c700e4bb19c0d991faff5345aff'] / Payload Auth. Tag /
]
Figure 28: Example 4: BCB Abstract Security Block (CBOR
Diagnostic Notation)
The CBOR encoding of the BCB block-type-specific-data field (the
abstract security block) is 0x820301020182028202018382014c5477656c766
531323132313282020382040782820150c95ed4534769b046d716e1cdfd00830e8201
500e365c700e4bb19c0d991faff5345aff.
A.4.4.3. Representations
The BCB wrapping this abstract security block is as follows.
[
12, / type code /
2, / block number /
1, / flags - block must be replicated in every fragment /
0, / CRC type /
h'820301020182028202018382014c5477656c7665313231323132820203820407
82820150c95ed4534769b046d716e1cdfd00830e8201500e365c700e4bb19c0d
991faff5345aff',
]
Figure 29: Example 4: BCB (CBOR Diagnostic Notation)
The CBOR encoding of the BCB block is 0x850c0201005847820301020182028
202018382014c5477656c766531323132313282020382040782820150c95ed4534769
b046d716e1cdfd00830e8201500e365c700e4bb19c0d991faff5345aff.
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A.4.5. Final Bundle
The CBOR encoding of the full output bundle, with the security blocks
added and payload block and BIB encrypted is: 0x9f8807000082028201028
2028202018202820201820018281a000f4240850b0300005845438ed6208eb1c1ffb9
4d952175167df0902a815f221ebc837a134efc13bfa82a2d5d317747da3eb54acef4c
a839bd961487284404259b60be12b8aed2f3e8a362836529f66 850c0201005847820
301020182028202018382014c5477656c766531323132313282020382040782820150
c95ed4534769b046d716e1cdfd00830e8201500e365c700e4bb19c0d991faff5345af
f8501010000582090eab64575930498d6aa654107f15e96319bb227706000abc8fcac
3b9bb9c87eff.
Appendix B. CDDL Expression
For informational purposes, Brian Sipos has kindly provided an
expression of the IPPT and AAD structures using the Concise Data
Definition Language (CDDL). That CDDL expression is presented below.
Note that wherever the CDDL expression is in disagreement with the
textual representation of the security block specification presented
in earlier sections of this document, the textual representation
rules.
Note that the structure of BP bundles and BPSec security blocks are
provided by other specifications and this section only provides the
CDDL expression for structures uniquely defined in this
specification. Items related to elements of a bundle, such as
"primary-block", are defined in Appendix B of the Bundle Protocol
Version 7 [I-D.ietf-dtn-bpbis].
Note that the CDDL itself does not have the concept of unadorned CBOR
sequences as a top-level subject of a specification. The current
best practice, as documented in Section 4.1 of [RFC8742], requires
representing the sequence as an array with a comment in the CDDL
noting that the array represents a CBOR sequence.
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start = scope / AAD-list / IPPT-list ; satisfy CDDL decoders
scope = uint .bits scope-flags
scope-flags = &(
has-primary-ctx: 0,
has-target-ctx: 1,
has-security-ctx: 2,
)
; Encoded as a CBOR sequence
AAD-list = [
AAD-structure
]
; Encoded as a CBOR sequence
IPPT-list = [
AAD-structure,
target-btsd: bstr ; block-type-specific-data of the target block.
]
AAD-structure = (
scope,
? primary-block, ; present if has-primary-ctx flag set
? block-metadata, ; present if has-target-ctx flag set
? block-metadata, ; present if has-security-ctx flag set
)
; Selected fields of a canonical block
block-metadata = (
block-type-code: uint,
block-number: uint,
block-control-flags,
)
Figure 30: IPPT and AAD Expressions
Appendix C. Acknowledgements
Amy Alford of the Johns Hopkins University Applied Physics Laboratory
contributed useful review and analysis of these security contexts.
Authors' Addresses
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Edward J. Birrane, III
The Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Rd.
Laurel, MD 20723
United States of America
Phone: +1 443 778 7423
Email: Edward.Birrane@jhuapl.edu
Alex White
The Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Rd.
Laurel, MD 20723
United States of America
Phone: +1 443 778 0845
Email: Alex.White@jhuapl.edu
Sarah Heiner
The Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Rd.
Laurel, MD 20723
United States of America
Phone: +1 240 592 3704
Email: Sarah.Heiner@jhuapl.edu
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