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Delay-Tolerant Networking                                       B. Sipos
Internet-Draft                                           RKF Engineering
Intended status: Standards Track                           June 26, 2020
Expires: December 28, 2020


          DTN Bundle Protocol Security COSE Security Contexts
                     draft-bsipos-dtn-bpsec-cose-01

Abstract

   This document defines an integrity security context and a
   confidentiality security context suitable for using CBOR Object
   Signing and Encryption (COSE) algorithms within Bundle Protocol
   Security (BPSec) blocks.  A profile of COSE is also defined for BPSec
   interoperation.

Status of This Memo

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

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

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

   This Internet-Draft will expire on December 28, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  BPSec Security Contexts . . . . . . . . . . . . . . . . . . .   3
     3.1.  COSE Integrity Context  . . . . . . . . . . . . . . . . .   3
     3.2.  COSE Confidentiality Context  . . . . . . . . . . . . . .   4
   4.  COSE Profile for BPSec  . . . . . . . . . . . . . . . . . . .   5
     4.1.  Interoperability Algorithms . . . . . . . . . . . . . . .   5
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     6.1.  Threat: BPSec Block Replay  . . . . . . . . . . . . . . .   8
     6.2.  Threat: Unidentifiable Key  . . . . . . . . . . . . . . .   8
     6.3.  Threat: Algorithm Vulnerabilities . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  BPSec Security Contexts . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  10
     A.1.  Symmetric Key COSE_Mac0 . . . . . . . . . . . . . . . . .  10
     A.2.  RSA Keypair COSE_Sign1  . . . . . . . . . . . . . . . . .  12
     A.3.  Symmetric Key COSE_Encrypt0 . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The Bundle Protocol Security (BPSec) Specification
   [I-D.ietf-dtn-bpsec] defines structure and encoding for Block
   Integrity Block (BIB) and Block Confidentiality Block (BCB) types but
   does not specify any security contexts to be used by either of the
   security block types.  The CBOR Object Signing and Encryption (COSE)
   specification [RFC8152] defines a structure, encoding, and algorithms
   to use for cryptographic signing and encryption.

   This document describes how to use the algorithms and encodings of
   COSE within BPSec blocks to apply those algorithms to Bundle security
   in Section 3.  A bare minimum of interoperability algorithms and
   algorithm parameters is specified by this document in Section 4.

   This document does not address how those COSE algorithms are intended
   to be used within a larger security context.








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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.  BPSec Security Contexts

   Rather than defining a single security context for both integrity and
   confidentiality blocks, this document specifies two separate security
   contexts which are analogous to the two BPSec block types.  Each
   security context allows a specific set of BPSec Result IDs.

   The existing COSE message-marking tags in Section 2 of [RFC8152]
   SHALL be used as BPSec Result ID values for all COSE security
   contexts (see Table 1 and Table 2).  This avoids the need for value-
   mapping between code points of the two registries.

   When embedding COSE messages, the CBOR-tagged form SHALL NOT be used.
   The Result ID values already provide the same information as the COSE
   tags.

3.1.  COSE Integrity Context

   The COSE Integrity Context has a Security Context ID of TBD-CI.

   The integrity context SHALL allow only the Result IDs from Table 1.
   Each integrity context result value SHALL consist of the COSE message
   indicated by Table 1 in its decoded form.

                      +-----------+----------------+
                      | Result ID | Result Message |
                      +-----------+----------------+
                      | 97        | COSE_Mac       |
                      |           |                |
                      | 17        | COSE_Mac0      |
                      |           |                |
                      | 98        | COSE_Sign      |
                      |           |                |
                      | 18        | COSE_Sign1     |
                      +-----------+----------------+

                      Table 1: COSE Integrity Results

   Each integrity result SHALL use the "detached" payload form with nil
   payload value.  The integrity result for COSE_Mac and COSE_Mac0



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   messages are computed by the procedure in Section 6.3 of [RFC8152].
   The integrity result for COSE_Sign and COSE_Sign1 messages are
   computed by the procedure in Section 4.4 of [RFC8152].

   [NOTE: This differs from base BPSec in that the entire block and the
   bundle primary is signed] The COSE "payload" used to generate a
   signature or MAC result SHALL be the canonically serialized target
   block, including the canonical block array structure.  The COSE
   "protected attributes from the application" used to generate a
   signature or MAC result SHALL be either:

   For a primary block target:  An empty byte string.

   For a canonical block target:  The canonically serialized primary
      block of the bundle.

3.2.  COSE Confidentiality Context

   The COSE Confidentiality Context has a Security Context ID of TBD-CC.

   The confidentiality context SHALL allow only the Result IDs from
   Table 2.  Each confidentiality context result value SHALL consist of
   the COSE message indicated by Table 2 in its decoded form.

                      +-----------+----------------+
                      | Result ID | Result Message |
                      +-----------+----------------+
                      | 96        | COSE_Encrypt   |
                      |           |                |
                      | 16        | COSE_Encrypt0  |
                      +-----------+----------------+

                   Table 2: COSE Confidentiality Results

   Only algorithms which support Authenticated Encryption with
   Authenticated Data (AEAD) SHALL be usable in the first (content)
   layer of a confidentiality result.  Because COSE encryption with AEAD
   appends the authentication tag with the ciphertext, the size of the
   block-type-specific-data will grow after an encryption operation.

   Each confidentiality result SHALL use the "detached" payload form
   with nil payload value.  The COSE plaintext and ciphertext correspond
   exactly with the target block-type-specific-data.  The
   confidentiality result for COSE_Encrypt and COSE_Encrypt0 messages
   are computed by the procedure in Section 5.3 of [RFC8152].

   [NOTE: This differs from base BPSec in that AAD from the block and
   the bundle primary is used] The COSE "plaintext" used to generate an



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   encrypt result SHALL be the block-type-specific-data of the target
   block, the decoded byte string itself (not including the encoded CBOR
   item header).  The COSE "protected attributes from the application"
   used to generate an encrypt result SHALL be the concatenation of the
   following:

   1.  The canonically serialized primary block of the bundle.

   2.  The canonically serialized augmented target block, which has its
       block-type-specific-data substituted with an empty byte string.

4.  COSE Profile for BPSec

   This section contains requirements which apply to the use of COSE
   within BPSec across any security context use.

   When used in a BPSec result, each COSE message SHALL contain an
   explicit algorithm identifier in the lower (content) layers.  A BPSec
   security operation always occurs within the context of the immutable
   primary block and its parameters.  When available and not implied by
   the bundle source, a COSE message SHOULD contain a key identifier in
   the highest layer.  When a key identifier is not available, BPSec
   acceptors SHOULD use the Security Source (if available) and the
   Bundle Source to imply which keys can be used for security
   operations.

   The algorithms required by this profile focuses on networks using
   shared symmetric-keys, with recommended algorithms for Elliptic Curve
   (EC) keypairs and RSA keypairs.  The focus of this profile is to
   enable interoperation between security sources and acceptors on an
   open network, where more explicit COSE parameters make it easier for
   BPSec acceptors to avoid assumptions and avoid out-of-band
   parameters.  The requirements of this profile still allow the use of
   potentially not-easily-interoperable algorithms and message/recipient
   configurations for use by private networks, where message size is
   more important than explicit COSE parameters.

4.1.  Interoperability Algorithms

   [NOTE: The required list is identical to the
   [I-D.ietf-dtn-bpsec-interop-sc] list.]  The set of integrity
   algorithms needed for interoperability is listed here.  The full set
   of COSE algorithms available is managed at [IANA-COSE].

   Implementations conforming to this specification SHALL support the
   symmetric keyed algorithms of Table 3.  Implementations capable of
   doing so SHOULD support the asymmetric keyed and key-encryption
   algorithms of Table 3.



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   +------------------+--------+-------------+------+------------------+
   | BPSec Block      | COSE   | Name        | Code | Implementation   |
   |                  | Layer  |             |      | Requirements     |
   +------------------+--------+-------------+------+------------------+
   | Integrity        | 1      | HMAC        | 5    | Required         |
   |                  |        | 256/256     |      |                  |
   |                  |        |             |      |                  |
   | Integrity        | 1      | ES256       | -7   | Recommended      |
   |                  |        |             |      |                  |
   | Integrity        | 1      | PS256       | -37  | Recommended      |
   |                  |        |             |      |                  |
   | Confidentiality  | 1      | A256GCM     | 3    | Required         |
   |                  |        |             |      |                  |
   | Confidentiality  | 2      | A256KW      | -5   | Recommended      |
   |                  |        |             |      |                  |
   | Integrity or     | 2      | ECDH-ES +   | -31  | Recommended      |
   | Confidentiality  |        | A256KW      |      |                  |
   |                  |        |             |      |                  |
   | Integrity or     | 2      | RSAES-OAEP  | -41  | Recommended      |
   | Confidentiality  |        | w/ SHA-256  |      |                  |
   +------------------+--------+-------------+------+------------------+

                   Table 3: Interoperability Algorithms

   The following are recommended key and recipient uses within COSE/
   BPSec:

   Symmetric Key Integrity:  When generating a BIB result from a
      symmetric key, implementations SHOULD use either a COSE_Mac0 or a
      COSE_Mac using the private key directly.  When a COSE_Mac is used
      with a direct key, the recipient layer SHOULD include a key
      identifier.

   EC Keypair Integrity:  When generating a BIB result from an EC
      keypair, implementations SHOULD use either a COSE_Sign1 or a
      COSE_Sign using the private key directly or a COSE_Mac from a
      symmetric key with a layer-2 encryption of the symmetric key.
      When a COSE_Sign or COSE_Mac is used with EC keypair, the
      recipient layer SHOULD include a public key identifier.

   RSA Keypair Integrity:  When generating a BIB result from an RSA
      keypair, implementations SHOULD use either a COSE_Sign1 or a
      COSE_Sign using the private key directly or a COSE_Mac from a
      symmetric key with a layer-2 key-wrap of the symmetric key.  When
      a COSE_Sign or COSE_Mac is used with RSA keypair, the recipient
      layer SHOULD include a public key identifier.  When a COSE_Sign or
      COSE_Sign1 is used with RSA keypair, the signature uses a maximum-
      length PSS salt in accordance with [RFC8230].



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   Symmetric Key Confidentiality:  When generating a BCB result from an
      symmetric key, implementations SHOULD use a COSE_Encrypt message
      with a recipient containing a key-wrapped CEK.  When generating a
      BCB result from a symmetric key, implementations SHOULD NOT use
      COSE_Encrypt0 or COSE_Encrypt with direct content encryption key
      (CEK).  Doing so risks key overuse and the vulnerabilities
      associated with large amount of ciphertext from the same key.

   EC Keypair Confidentiality:  When generating a BCB result from an EC
      keypair, implementations SHOULD use a COSE_Encrypt message with a
      recipient containing a key-wrapped CEK.

   RSA Keypair Confidentiality:  When generating a BCB result from an
      RSA keypair, implementations SHOULD use a COSE_Encrypt message
      with a recipient containing a key-wrapped CEK.

5.  Implementation Status

   [NOTE to the RFC Editor: please remove this section before
   publication, as well as the reference to [RFC7942] and
   [github-dtn-bpsec-cose].]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations can
   exist.

   An example implementation of COSE over Blocks has been created as a
   GitHub project [github-dtn-bpsec-cose] and is intended to use as a
   proof-of-concept and as a possible source of interoperability
   testing.  This example implementation only handles CBOR encoding/
   decoding and cryptographic functions, it does not construct actual
   BIB or BCB and does not integrate with a BP Agent.

6.  Security Considerations

   This section separates security considerations into threat categories
   based on guidance of BCP 72 [RFC3552].





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   All of the security considerations of the underlying BPSec
   [I-D.ietf-dtn-bpsec] apply to these new security contexts.

6.1.  Threat: BPSec Block Replay

   The bundle's primary block contains fields which uniquely identify a
   bundle: the Source Node ID, Creation Timestamp, and fragment
   parameters (see Section 4.2.2 of [I-D.ietf-dtn-bpbis]).  These same
   fields are used to correlate Administrative Records with the bundles
   for which the records were generated.  Including the primary block in
   the AAD for BPSec integrity and confidentiality binds the
   verification of the secured block to its parent bundle and disallows
   replay of any block with its BIB or BCB.

   This profile of COSE limits the encryption algorithms to only AEAD in
   order to include the context of the encrypted data as AAD.  If an
   agent mistakenly allows the use of non-AEAD encryption when
   decrypting and verifying a BCB, the possibility of block replay
   attack is present.

6.2.  Threat: Unidentifiable Key

   The profile in Section 4.1 recommends key identifiers when possible.
   If the application using a COSE Integrity or COSE Confidentiality
   context leaves out key identification data (in a COSE recipient
   structure), the security acceptor for those BPSec blocks only has the
   primary block available to use when verifying or decrypting the
   target block.  This leads to a situation, identified in BPSec
   Security Considerations, where a signature is verified to be valid
   but not from the expected Security Source.

6.3.  Threat: Algorithm Vulnerabilities

   Because this use of COSE leaves the specific algorithms chosen for
   BIB and BCB use up to the applications securing bundle data, it is
   important to use only COSE algorithms which are marked as recommended
   in the IANA registry [IANA-COSE].

7.  IANA Considerations

   Registration procedures referred to in this section are defined in
   [RFC8126].

7.1.  BPSec Security Contexts

   Within the "Bundle Protocol" registry [IANA-BUNDLE], the following
   entry has been added to the "BPSec Security Context Identifiers" sub-
   registry.



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          +--------+----------------------+---------------------+
          | Value  | Description          | Reference           |
          +--------+----------------------+---------------------+
          | TBD-CI | COSE Integrity       | This specification. |
          |        |                      |                     |
          | TBD-CC | COSE Confidentiality | This specification. |
          +--------+----------------------+---------------------+

8.  Acknowledgments

   The interoperability minimum algorithms and parameters are based on
   the draft [I-D.ietf-dtn-bpsec-interop-sc].

9.  References

9.1.  Normative References

   [I-D.ietf-dtn-bpsec]
              Birrane, E. and K. McKeever, "Bundle Protocol Security
              Specification", draft-ietf-dtn-bpsec-22 (work in
              progress), March 2020.

   [IANA-BUNDLE]
              IANA, "Bundle Protocol",
              <https://www.iana.org/assignments/bundle/>.

   [IANA-COSE]
              IANA, "CBOR Object Signing and Encryption (COSE)",
              <https://www.iana.org/assignments/cose/>.

   [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>.

   [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>.




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   [RFC8230]  Jones, M., "Using RSA Algorithms with CBOR Object Signing
              and Encryption (COSE) Messages", RFC 8230,
              DOI 10.17487/RFC8230, September 2017,
              <https://www.rfc-editor.org/info/rfc8230>.

9.2.  Informative References

   [github-dtn-bpsec-cose]
              Sipos, B., "DTN Bundle Protocol Security COSE Security
              Contexts",
              <https://github.com/BSipos-RKF/dtn-bpsec-cose/>.

   [I-D.ietf-dtn-bpbis]
              Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol
              Version 7", draft-ietf-dtn-bpbis-25 (work in progress),
              May 2020.

   [I-D.ietf-dtn-bpsec-interop-sc]
              Birrane, E., "BPSec Interoperability Security Contexts",
              draft-ietf-dtn-bpsec-interop-sc-01 (work in progress),
              February 2020.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,
              <https://www.rfc-editor.org/info/rfc3552>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

Appendix A.  Examples

A.1.  Symmetric Key COSE_Mac0

   This is an example of a MAC with implied recipient (and its key
   material).  The two provided figures are CBOR diagnostic notation
   [RFC7049] of the target block being signed and the Abstract Security
   Block (which will itself be enveloped within a BIB).

   The 256-bit key used is shown below.





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   / signing key /
   h'13bf9cead057c0aca2c9e52471ca4b19ddfaf4c0784e3f3e8e3999dbae4ce45c'

                               Symmetric Key

   [
     7, / BP version /
     0, / flags /
     0, / CRC type /
     [1, '//dst/'], / destination /
     [1, '//src/'], / source /
     [1, '//src/'], / report-to /
     [0, 40], / timestamp /
     1000000 / lifetime /
   ]

                  Figure 1: Primary block CBOR diagnostic

   [
     7, / type code - bundle age /
     2, / block num /
     0, / flags /
     0, / CRC type /
     h'19012c' / type-specific-data:
       300 \ age \
     /
   ]

                  Figure 2: Target block CBOR diagnostic

   The external_aad is the encoded primary block.  The payload is the
   encoded target block.

[
  'MAC0', / context /
  h'a10105', / protected /
  h'880700008201462f2f6473742f8201462f2f7372632f8201462f2f7372632f820018
    281a000f4240', / external_aad /
  h'85070200004319012c' / payload /
]

                  Figure 3: MAC_structure CBOR diagnostic









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[
  [2], / targets /
  0, / security context TBD /
  0, / flags /
  [
    [ / target block #2 /
      [ / result /
        17, / COSE_Mac0 tag /
        [
          h'a10105' / protected {
             \ alg \ 1:5 \ HMAC 256//256 \
           } / ,
          { / unprotected /
            / kid / 4:'mykey'
          },
          null, / payload /
          h'd98308918d36dc4190a93f84c8d857015b75b78edea3360282555257c3be
            f847' / tag /
        ]
      ]
    ]
  ]
]

             Figure 4: Abstract Security Block CBOR diagnostic

A.2.  RSA Keypair COSE_Sign1

   This is an example of a signature with implied recipient (and its key
   material).  The two provided figures are CBOR diagnostic notation
   [RFC7049] of the target block being signed and the Abstract Security
   Block (which will itself be enveloped within a BIB).

   The 512-bit private key used is below.  It is not supposed to be a
   secure configuration, only intended to explain the procedure.  This
   signature uses zero-length salt for deterministic output, which
   differs from the parameter specified by [RFC8230] and is not
   recommended for normal use.

   -----BEGIN RSA PRIVATE KEY-----
   MIIBOwIBAAJBAN21GdS0faAYgacepRmbr7TAT0wEuahjrBfAO0Dg1M5d37O9Tx9H
   vZw2OEcLq2WTvf0Kja1JWpqdoJm17LghhPkCAwEAAQJBAMgkJo9n6EhQFyrgdTZq
   3vES8gKz+U3TvJUsSdFFpZYsZhUaLKP9oxyIxl3IvK5iS0oAsW0nqI7aMcBoPmxZ
   pQECIQDuyd5uzvS0wnrsDWoDhiTm6O+PJoMQix9yH99HBUhWKQIhAO2wDP7e/Nnr
   A7rDSgM6+REGmt8I00NglFwShBUi4HJRAiAiJrLuTCEJXSsxaXW5DU1nzPa+FXb3
   Pb6Alvha8vF2iQIgbC7WK2dJBNKv9uCOHlxIItSzxtIYfjFGNYYD8i7Wo5ECIQDp
   5++fp04AMVAnE0uqNEnITkTWb91hAS8IjaYCqLGyEA==
   -----END RSA PRIVATE KEY-----



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   [
     7, / BP version /
     0, / flags /
     0, / CRC type /
     [1, '//dst/'], / destination /
     [1, '//src/'], / source /
     [1, '//src/'], / report-to /
     [0, 40], / timestamp /
     1000000 / lifetime /
   ]

                  Figure 5: Primary block CBOR diagnostic

   [
     7, / type code - bundle age /
     2, / block num /
     0, / flags /
     0, / CRC type /
     h'19012c' / type-specific-data:
       300 \ age \
     /
   ]

                  Figure 6: Target block CBOR diagnostic

   The external_aad is the encoded primary block.  The payload is the
   encoded target block.

[
  'Signature1', / context /
  h'a1013824', / protected /
  h'880700008201462f2f6473742f8201462f2f7372632f8201462f2f7372632f820018
    281a000f4240', / external_aad /
  h'85070200004319012c' / payload /
]

                  Figure 7: Sig_structure CBOR diagnostic














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[
  [2], / targets /
  0, / security context TBD /
  0, / flags /
  [
    [ / target block #2 /
      [ / result /
        18, / COSE_Sign1 tag /
        [
          h'a1013824' / protected {
             \ alg \ 1:-37 \ PS256 \
           } / ,
          { / unprotected /
            / kid / 4:'mykey'
          },
          null, / payload /
          h'1a35746072396c74275fd7b443a0d7391a0f92012a53e0accc543daa51ae
            6faae551a4843a0bc7c3bf808e3638ddc381355b54cc60f4ca9dea15923b
            5986e758' / signature /
        ]
      ]
    ]
  ]
]

             Figure 8: Abstract Security Block CBOR diagnostic

A.3.  Symmetric Key COSE_Encrypt0

   This is an example of an encryption with implied recipient (and its
   direct content encryption key).  The provided figures are CBOR
   diagnostic notation [RFC7049] of the target block being encrypted,
   the Abstract Security Block (which will itself be enveloped within a
   BCB), and the resulting target block.

   This example uses a single shared content encryption key, which is
   not recommended for normal use.  The 256-bit key used is shown below.
   A random IV is generated for this operation and is indicated in a
   standard way in the unprotected header.

   / content encryption key /
   h'13bf9cead057c0aca2c9e52471ca4b19ddfaf4c0784e3f3e8e3999dbae4ce45c'

                              Symmetric Keys







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   [
     7, / BP version /
     0, / flags /
     0, / CRC type /
     [1, '//dst/'], / destination /
     [1, '//src/'], / source /
     [1, '//src/'], / report-to /
     [0, 40], / timestamp /
     1000000 / lifetime /
   ]

                  Figure 9: Primary block CBOR diagnostic

   [
     7, / type code - bundle age /
     2, / block num /
     0, / flags /
     0, / CRC type /
     h'19012c' / type-specific-data:
       300 \ age \
     /
   ]

              Figure 10: Initial Target block CBOR diagnostic

   The external_aad is a concatenation of the encoded primary block and
   the encoded augmented target block (its block data removed).

[
  'Encrypt0', / context /
  h'a10103', / protected /
  h'880700008201662f2f6473742f8201662f2f7372632f8201662f2f7372632f820018
    281a000f4240850702000040' / external_aad /
]

                 Figure 11: Enc_structure CBOR diagnostic















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   [
     [2], / targets /
     0, / security context TBD /
     0, / flags /
     [
       [ / target block #2 /
         [ / result /
           16, / COSE_Encrypt0 tag /
           [
             h'a10103', / protected {
                \ alg \ 1:3 \ A256GCM \
              } /
             { / unprotected /
               / kid / 4:'mykey',
               / iv / 5: h'6f3093eba5d85143c3dc484a'
             },
             null / payload /
           ]
         ]
       ]
     ]
   ]

            Figure 12: Abstract Security Block CBOR diagnostic

   [
     7, / type code - bundle age /
     2, / block num /
     0, / flags /
     0, / CRC type /
     h'63bb16685ef432a0e6f1d404da71959081a715' / ciphertext /
   ]

             Figure 13: Encrypted Target block CBOR diagnostic

Author's Address

   Brian Sipos
   RKF Engineering Solutions, LLC
   7500 Old Georgetown Road
   Suite 1275
   Bethesda, MD  20814-6198
   United States of America

   Email: BSipos@rkf-eng.com






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