Delay-Tolerant Networking                                       B. Sipos
Internet-Draft                                           RKF Engineering
Intended status: Standards Track                        22 December 2020
Expires: 25 June 2021


          DTN Bundle Protocol Security COSE Security Contexts
                     draft-bsipos-dtn-bpsec-cose-04

Abstract

   This document defines a security context suitable for using CBOR
   Object Signing and Encryption (COSE) algorithms within Bundle
   Protocol Security (BPSec) integrity and confidentiality 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.

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   This Internet-Draft will expire on 25 June 2021.

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   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
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   provided without warranty as described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  PKIX Environments and CA Policy . . . . . . . . . . . . .   4
     1.3.  Use of CDDL . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  BPSec Security Context  . . . . . . . . . . . . . . . . . . .   4
     3.1.  Security Scope  . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Key Containers  . . . . . . . . . . . . . . . . . . .   6
       3.2.2.  AAD Scope . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Results . . . . . . . . . . . . . . . . . . . . . . . . .   7
       3.3.1.  Integrity Messages  . . . . . . . . . . . . . . . . .   8
       3.3.2.  Confidentiality Messages  . . . . . . . . . . . . . .   9
     3.4.  Key Considerations  . . . . . . . . . . . . . . . . . . .  10
     3.5.  Canonicalization Algorithms . . . . . . . . . . . . . . .  10
       3.5.1.  Generating AAD  . . . . . . . . . . . . . . . . . . .  10
       3.5.2.  Payload Data  . . . . . . . . . . . . . . . . . . . .  11
     3.6.  Processing  . . . . . . . . . . . . . . . . . . . . . . .  11
       3.6.1.  Security Source Authentication  . . . . . . . . . . .  11
       3.6.2.  Policy Recommendations  . . . . . . . . . . . . . . .  12
   4.  COSE Profile for BPSec  . . . . . . . . . . . . . . . . . . .  12
     4.1.  COSE Messages . . . . . . . . . . . . . . . . . . . . . .  13
     4.2.  Interoperability Algorithms . . . . . . . . . . . . . . .  13
     4.3.  Asymmetric Key Types and Identifiers  . . . . . . . . . .  15
       4.3.1.  PKIX Certificates . . . . . . . . . . . . . . . . . .  16
   5.  PKIX Certificate Profile  . . . . . . . . . . . . . . . . . .  16
     5.1.  Multiple-Certificate Uses . . . . . . . . . . . . . . . .  17
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  18
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
     7.1.  Threat: BPSec Block Replay  . . . . . . . . . . . . . . .  18
     7.2.  Threat: Untrusted End-Entity Certificate  . . . . . . . .  19
     7.3.  Threat: Certificate Validation Vulnerabilities  . . . . .  19
     7.4.  Threat: BP Node Impersonation . . . . . . . . . . . . . .  19
     7.5.  Threat: Unidentifiable Key  . . . . . . . . . . . . . . .  20
     7.6.  Threat: Non-Trusted Public Key  . . . . . . . . . . . . .  20
     7.7.  Threat: Passive Leak of Key Material  . . . . . . . . . .  20
     7.8.  Threat: Algorithm Vulnerabilities . . . . . . . . . . . .  21
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
     8.1.  BPSec Security Contexts . . . . . . . . . . . . . . . . .  21
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  21
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     10.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  24
     A.1.  Symmetric Key COSE_Mac0 . . . . . . . . . . . . . . . . .  25
     A.2.  EC Keypair COSE_Sign1 . . . . . . . . . . . . . . . . . .  26



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     A.3.  RSA Keypair COSE_Sign1  . . . . . . . . . . . . . . . . .  29
     A.4.  Symmetric KEK COSE_Encrypt  . . . . . . . . . . . . . . .  32
     A.5.  EC Keypair COSE_Encrypt . . . . . . . . . . . . . . . . .  34
     A.6.  RSA Keypair COSE_Encrypt  . . . . . . . . . . . . . . . .  36
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  39

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.  The
   focus of the recommended algorithms is to allow BPSec to be used in a
   Public Key Infrastructure (PKI) as described in Section 1.2.

   Examples of specific uses are provided in Appendix A to aid in
   implementation support of the interoperability algorithms.

1.1.  Scope

   This document describes a profile of COSE which is tailored for use
   in BPSec and a method of including full COSE messages within BPSec
   security blocks.  This document does not address:

   *  Policies or mechanisms for issuing Public Key Infrastructure Using
      X.509 (PKIX) certificates; provisioning, deploying, or accessing
      certificates and private keys; deploying or accessing certificate
      revocation lists (CRLs); or configuring security parameters on an
      individual entity or across a network.

   *  Uses of COSE beyond the profile defined in this document.

   *  How those COSE algorithms are intended to be used within a larger
      security context.  Many header parameters used by COSE (e.g., key
      identifiers) depend on the network environment and security policy
      related to that environment.







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1.2.  PKIX Environments and CA Policy

   This specification gives requirements about how to use PKIX
   certificates issued by a Certificate Authority (CA), but does not
   define any mechanisms for how those certificates come to be.

   To support the PKIX uses defined in this document, the CA(s) issuing
   certificates for BP nodes are aware of the end use of the
   certificate, have a mechanism for verifying ownership of a Node ID,
   and are issuing certificates directly for that Node ID.  BPSec
   security acceptors authenticate the Node ID of security sources when
   verifying integrity (see Section 3.6.1) using a public key provided
   by a PKIX certificate (see Section 4.3.1) following the certificate
   profile of Section 5.

1.3.  Use of CDDL

   This document defines CBOR structure using the Concise Data
   Definition Language (CDDL) of [RFC8610].  The entire CDDL structure
   can be extracted from the XML version of this document using the
   XPath expression:

   '//sourcecode[@type="cddl"]'

   The following initial fragment defines the top-level symbols of this
   document's CDDL, including the ASB data structure with its parameter/
   result sockets.

   start = AAD-value / ext-data-asb

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 Context

   This document specifies a single security context for use in both
   BPSec integrity and confidentiality blocks.  This is done to save
   code points allocated to this specification and to simplify the
   encoding of COSE-in-BPSec; the BPSec block type uniquely defines the
   acceptable parameters and COSE messages which can be present.

   The COSE security context SHALL have the Security Context ID
   specified in Section 8.1.



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   Both types of security block can use the same parameters, defined in
   Section 3.2, to carry public key-related information and each type of
   security block allows specific COSE message results, defined in
   Section 3.3.

3.1.  Security Scope

   The scope here refers to the set of information used by the security
   context to cryptographically bind with the plaintext data being
   integrity-protected or confididentiality-protected.  This information
   is generically referred to as additional authenticated data (AAD),
   which is also the term used by COSE to describe the same data.

   The sources for AAD within the COSE context are described below,
   controlled by the AAD Scope Flags parameter of Section 3.2.2, and
   implemented as defined in Section 3.5.1.

   Bundle 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 target is no longer in its original bundle.  Including this
      data as part of AAD ensures that security target appears in the
      same bundle that the security source intended.

   Target Block Metadata  When the target block is a canonical block
      (i.e., not the primary block) it contains its block-type-specific
      data, which is the subject of the security operation, but also
      metadata identifying the block.  This metadata explicitly excludes
      the CRC type and value fields because the CRC is derived from the
      block-type-specific data.  Including this data as part of AAD
      ensures that the target data appears in the same block that the
      security source intended.

   Security Block Metadata  The BPSec block containing the security
      result for which the AAD is assembled also has metadata
      identifying the block.  Including this data as part of AAD ensures
      that the security result appears in the same block that the
      security source intended.

3.2.  Parameters

   Each COSE context parameter value SHALL consist of the COSE structure
   indicated by Table 1 in its decoded (CBOR item) form.  Each security
   block MAY contain any number of each parameter type.  When a
   parameter is not present, the security acceptor SHALL use the Default
   Value of Table 1.





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     +==============+=============+======================+===========+
     | Parameter ID | Parameter   | Reference            | Default   |
     |              | Structure   |                      | Value     |
     +==============+=============+======================+===========+
     | 1            | COSE_Key    | [RFC8152]            | none      |
     +--------------+-------------+----------------------+-----------+
     | 2            | COSE_KeySet | [RFC8152]            | none      |
     +--------------+-------------+----------------------+-----------+
     | 3            | COSE_X509   | [I-D.ietf-cose-x509] | none      |
     |              | as x5chain  |                      |           |
     +--------------+-------------+----------------------+-----------+
     | 4            | COSE_X509   | [I-D.ietf-cose-x509] | none      |
     |              | as x5bag    |                      |           |
     +--------------+-------------+----------------------+-----------+
     | 5            | AAD_Scope   | Section 3.2.2 of     | 0x7 (all  |
     |              |             | this RFC             | contexts) |
     +--------------+-------------+----------------------+-----------+

                     Table 1: COSE Security Parameters

   $bpsec-param-pair /= [1, COSE_Key]
   $bpsec-param-pair /= [2, COSE_KeySet]
   $bpsec-param-pair /= [3, x5chain: COSE_X509]
   $bpsec-param-pair /= [4, x5bag: COSE_X509]
   $bpsec-param-pair /= [5, AAD-scope]

                   Figure 1: COSE context parameters CDDL

3.2.1.  Key Containers

   Implementations capable of handling asymmetric-keyed algorithms
   SHOULD support the public key handling parameters of Table 1.  See
   Section 4.3 for a definition of how the aggregate of all public keys
   and certificates in security parameters apply to each security
   result.

   COSE security parameters SHALL NOT contain any private key material.
   The security parameters are all stored in the bundle as plaintext and
   are visible to any bundle handlers.

3.2.2.  AAD Scope

   The AAD Scope parameter controls what data is included in the AAD for
   both integrity and confidentiality operations.  The AAD Scope
   parameter SHALL be encoded as a unit value with bit flags defined in
   Table 2.  The default value for this parameter has all flags set
   which has the AAD include all available context.




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   A CDDL representation of this definition is included in Figure 2 for
   reference.

       +==================+========+===============================+
       | Name             | Code   | Description                   |
       +==================+========+===============================+
       | has-primary-ctx  | 0x01   | If bit is set, indicates that |
       |                  |        | the primary block is included |
       |                  |        | in AAD scope.                 |
       +------------------+--------+-------------------------------+
       | has-target-ctx   | 0x02   | If bit is set, indicates that |
       |                  |        | the target block metadata is  |
       |                  |        | included in AAD scope.        |
       +------------------+--------+-------------------------------+
       | has-security-ctx | 0x04   | If bit is set, indicates that |
       |                  |        | the security block metadata   |
       |                  |        | is included in AAD scope.     |
       +------------------+--------+-------------------------------+
       | Reserved         | others |                               |
       +------------------+--------+-------------------------------+

                          Table 2: AAD Scope Flags

   AAD-scope = uint .bits AAD-scope-flags
   AAD-scope-flags = &(
       has-primary-ctx: 0,
       has-target-ctx: 1,
       has-security-ctx: 2,
   )

                          Figure 2: AAD Scope CDDL

3.3.  Results

   Although each COSE context result is a COSE message, the types of
   message allowed depend upon the security block type in which the
   result is present: only MAC or signature messages are allowed in a
   BIB and only encryption messages are allowed in a BCB.

   The code points for Result ID values are identical to the existing
   COSE message-marking tags in Section 2 of [RFC8152].  This avoids the
   need for value-mapping between code points of the two registries.









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   When embedding COSE messages, the CBOR structure SHALL be directly
   included within the abstract security block (ASB) CBOR structure.
   There is no use of embedded encoded CBOR (e.g.  CBOR encoded as a
   byte string) in this specification.  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 (using the same code
   points).

   These generic requirements are formalized in the CDDL fragment of
   Figure 3.

   $bpsec-result-pair /= [16, COSE_Encrypt0]
   $bpsec-result-pair /= [17, COSE_Mac0]
   $bpsec-result-pair /= [18, COSE_Sign1]
   $bpsec-result-pair /= [96, COSE_Encrypt]
   $bpsec-result-pair /= [97, COSE_Mac]
   $bpsec-result-pair /= [98, COSE_Sign]

                    Figure 3: COSE context results CDDL

3.3.1.  Integrity Messages

   When used within a Block Integrity Block, the COSE context SHALL
   allow only the Result IDs from Table 3.  Each integrity result value
   SHALL consist of the COSE message indicated by Table 3 in its decoded
   form.

               +===========+==================+===========+
               | Result ID | Result Structure | Reference |
               +===========+==================+===========+
               | 97        | COSE_Mac         | [RFC8152] |
               +-----------+------------------+-----------+
               | 17        | COSE_Mac0        | [RFC8152] |
               +-----------+------------------+-----------+
               | 98        | COSE_Sign        | [RFC8152] |
               +-----------+------------------+-----------+
               | 18        | COSE_Sign1       | [RFC8152] |
               +-----------+------------------+-----------+

                     Table 3: 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
   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].





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   The COSE "protected attributes from the application" used for a
   signature or MAC result SHALL be the encoded data defined in
   Section 3.5.1.  The COSE payload used for a signature or MAC result
   SHALL be either the block-type-specific data of the target, if the
   target is not the primary block, or an empty byte string if the
   target is the primary block.

3.3.2.  Confidentiality Messages

   When used within a Block Confidentiality Block, COSE context SHALL
   allow only the Result IDs from Table 4.  Each confidentiality result
   value SHALL consist of the COSE message indicated by Table 4 in its
   decoded form.

               +===========+==================+===========+
               | Result ID | Result Structure | Reference |
               +===========+==================+===========+
               | 96        | COSE_Encrypt     | [RFC8152] |
               +-----------+------------------+-----------+
               | 16        | COSE_Encrypt0    | [RFC8152] |
               +-----------+------------------+-----------+

                  Table 4: 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.
   Security acceptors MUST NOT assume that the size of the plaintext is
   the same as the size of the ciphertext.

   Each confidentiality result SHALL use the "detached" payload form
   with nil payload value.  The confidentiality result for COSE_Encrypt
   and COSE_Encrypt0 messages are computed by the procedure in
   Section 5.3 of [RFC8152].

   The COSE "protected attributes from the application" used for an
   encryption result SHALL be the encoded data defined in Section 3.5.1.
   The COSE payload used for an encryption result SHALL be the block-
   type-specific data of the target.  Because confidentiality of the
   primary block is disallowed by BPSec, there is no logic here for
   handling a BCB with a target on the primary block.








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3.4.  Key Considerations

   This specification does not impose any additional key requirements
   beyond those already specified for each COSE algorithim required in
   Section 4.

3.5.  Canonicalization Algorithms

   Generating or processing COSE messages for the COSE context follows
   the profile defined in Section 4 with the "protected attributes from
   the application" (i.e., the "external_aad" item) generated as defined
   in Section 3.5.1.

3.5.1.  Generating AAD

   The AAD used for both integrity and confidentiality messages SHALL be
   the determistically encoded form of a CBOR array containing the
   following:

   1.  The first item SHALL be either: the CBOR array (unencoded) form
       of the primary block of the bundle if the AAD Scope has the has-
       primary-ctx flag set, otherwise the null value.

   2.  The second item SHALL be either: a CBOR array containing the
       first three fields of the target block (i.e., the block type
       code, block number, and control flags) if the AAD Scope has the
       has-target-ctx flag set, otherwise the null value.

   3.  The third item SHALL be either: a CBOR array containing the first
       three fields of the security block containing the result (i.e.,
       the block type code, block number, and control flags) if the AAD
       Scope has the has-security-ctx flag set, otherwise the null
       value.

   A CDDL representation of this data is shown below in Figure 4.

   AAD-value = bstr .cbor AAD-structure
   AAD-structure = [
       primary-ctx:  null / primary-block,  ; if has-primary-ctx is set
       target-ctx:   null / block-metadata, ; if has-target-ctx is set
       security-ctx: null / block-metadata  ; if has-security-ctx is set
   ]
   ; The first three fields of BP "canonical-block-structure"
   block-metadata = [
       block-type-code: uint,
       block-number: uint,
       block-control-flags,
   ]



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                      Figure 4: COSE context AAD CDDL

3.5.2.  Payload Data

   When correlating between BPSec target block-type-specific-data and
   COSE plaintext or payload, any byte string SHALL be handled in its
   decoded (CBOR item) form.  This means any CBOR header or tag in a
   source encoding are ignored for the purposes of security processing.
   This also means that if the source byte string was encoded in a non-
   conforming way, for example in indefinite-length form or with a non-
   minimum-size lengnth, the security processing always treats it in a
   determistically encoded CBOR form.

3.6.  Processing

   This section describes block-level requirements for handling COSE
   security data.

   Security results generated for BIB or BCB results SHALL conform to
   the COSE profile of Section 4.  Security acceptors SHOULD

3.6.1.  Security Source Authentication

   This section explains how the certificate profile of Section 5 is
   used by a security acceptor to both validate an end-entity
   certificate and to use that certificate to authenticate the security
   source for the COSE security context.

   Because of the standard policy of using separate certificates for
   transport, signing, and encryption (see Section 5.1) a single Node ID
   is likely to be associated with mulitple certificates, and any or all
   of those certificates can be present as security parameters (see
   Section 3.2.1).  When present, a security acceptor SHALL use an "x5t"
   identifier from a COSE recipient to identify an end-entity
   certificate to use for result processing.  Security acceptors SHALL
   NOT assume that a validated certificate containing a NODE-ID matching
   a security source is enough to associate a certificate with a COSE
   message or recipient.

3.6.1.1.  Certificate Path and Purpose Validation

   For each end-entity certificate referenced by a COSE context result,
   the security acceptor SHALL perform the certification path validation
   of [RFC5280] up to one of the acceptor's trusted CA certificates.  If
   enabled by local policy, the entity SHALL perform an OCSP check of
   each certificate providing OCSP authoritiy information in accordance
   with [RFC6960].  If certificate validation fails or if security
   policy disallows a certificate for any reason, the acceptor SHALL



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   treat the associated security result as failed.  Leaving out part of
   the certification chain can cause the entity to fail to validate a
   certificate if the left-out certificates are unknown to the entity
   (see Section 7.2).

   For each end-entity certificate referenced by a COSE context result,
   the security acceptor SHALL apply security policy to the Key Usage
   extension (if present) and Extended Key Usage extension (if present)
   in accordance with Section 4.2.1.12 of [RFC5280] and the profile in
   Section 5.

3.6.1.2.  Node ID Authentication

   If required by security policy, for each end-entity certificate
   referenced by a COSE context result the security acceptor SHALL
   validate the certificate NODE-ID in accordance with Section 6 of
   [RFC6125] using the NODE-ID reference identifier from either the
   Security Source (if present) or the Bundle Source (as the implied
   security source).  If the NODE-ID validation result is Failure or if
   the result is Absent and security policy requires an authenticated
   Node ID, the security acceptor SHALL treat the result as failed.

3.6.2.  Policy Recommendations

   A RECOMMENDED security policy is to enable the use of OCSP checking
   when internet connectivity is present.  A RECOMMENDED security policy
   is that if an Extended Key Usage is present that it needs to contain
   "id-kp-bundleSecurity" to be usable as an end-entity certificate for
   with COSE security results.  A RECOMMENDED security policy is to
   require a validated Node ID (of Section 3.6.1.2) and to ignore any
   other identifiers in the end-entity certificate.

   This policy relies on and informs the certificate requirements in
   Section 4.3.1.  This policy assumes that a DTN-aware CA (see
   Section 1.2) will only issue a certificate for a Node ID when it has
   verified that the private key holder actually controls the DTN node;
   this is needed to avoid the threat identified in Section 7.4.  This
   policy requires that a certificate contain a NODE-ID and allows the
   certificate to also contain network-level identifiers.  A tailored
   policy on a more controlled network could relax the requirement on
   Node ID validation and/or Extended Key Usage presence.

4.  COSE Profile for BPSec

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





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4.1.  COSE Messages

   When generating a BPSec result, security sources SHALL use encode
   COSE labels with a uint value.  When processing a BPSec result,
   security acceptors MAY handle COSE labels with with a tstr value.

   When used in a BPSec result, each COSE message SHALL contain an
   explicit algorithm identifier in the lower (content) layers.  When
   available and not implied by the bundle source, a COSE message SHALL
   contain a key identifier in the highest (recipient) layer.  See
   Section 4.3 for specifics about asymmetric key identifiers.  When a
   key identifier is not available, BPSec acceptors SHALL use the
   Security Source (if available) and the Bundle Source to imply which
   keys can be used for security operations.  Using implied keys has an
   interoperability risk, see Section 7.5 for details.  A BPSec security
   operation always occurs within the context of the immutable primary
   block with its parameters (specifically the Source Node ID) and the
   security block with its optional Security Source.

   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.

4.2.  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 and key-encryption algorithms of Table 5.
   Implementations capable of doing so SHOULD support the asymmetric
   keyed and key-encryption algorithms of Table 5.










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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          | EdDSA      | -8   | Recommended    |
   +-----------------+------------+------------+------+----------------+
   | Integrity       | 1          | PS256      | -37  | Recommended    |
   +-----------------+------------+------------+------+----------------+
   | Confidentiality | 1          | A256GCM    | 3    | Required       |
   +-----------------+------------+------------+------+----------------+
   | Confidentiality | 2          | A256KW     | -5   | Required       |
   +-----------------+------------+------------+------+----------------+
   | Confidentiality | 2          | ECDH-ES +  | -31  | Recommended    |
   |                 |            | A256KW     |      |                |
   +-----------------+------------+------------+------+----------------+
   | Confidentiality | 2          | RSAES-OAEP | -41  | Recommended    |
   |                 |            | w/ SHA-256 |      |                |
   +-----------------+------------+------------+------+----------------+

                    Table 5: 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 SHALL 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.  When a COSE_Sign is
      used with an EC keypair, the recipient layer SHALL include a
      public key identifier (see Section 4.3).

   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.  When a COSE_Sign is
      used with an RSA keypair, the recipient layer SHALL include a
      public key identifier (see Section 4.3).  When a COSE_Sign or
      COSE_Sign1 is used with an RSA keypair, the signature uses a PSS
      salt in accordance with Section 2 of [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.
      When a COSE_Encrypt is used with an overall key-encryption key
      (KEK), the recipient layer SHALL include a key identifier for the
      KEK.

   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.  When a COSE_Encrypt is
      used with an EC keypair, the recipient layer SHALL include a
      public key identifier (see Section 4.3).  When a COSE_Encrypt is
      used with an EC keypair, the security source SHALL generate an
      ephemeral EC keypair for each security operation.  When processing
      a COSE_Encrypt with an EC keypair, the security acceptor SHALL
      process all KDF and HMAC context data from the recipient headers
      in accordance with Section 11.2 of [RFC8152] even though the
      source is not required to provide any of those parameters.

   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.  When a
      COSE_Encrypt is used with an RSA keypair, the recipient layer
      SHALL include a public key identifier (see Section 4.3).

4.3.  Asymmetric Key Types and Identifiers

   This section applies when a BIB uses a public key for verification,
   or when a BCB uses a public key for encryption.  When using
   asymmetric keyed algorithms, the security source SHALL include a
   public key identifier as a recipient header.  The public key
   identifier SHALL be either a "kid" [RFC8152], an "x5t"
   [I-D.ietf-cose-x509], or an equivalent identifier.

   When a BIB result contains a "kid" identifier, the security source
   SHOULD include an appropriate COSE public key in the security
   parameters.  When BIB result contains a "x5t" identifier, the
   security source SHOULD include an appropriate PKIX certificate chain
   in the security parameters.  For a BIB, if all potential security
   acceptors are known to possess related public key and/or certificate
   data then the public key parameters can be omitted.  Risks of not
   including related data are described in Section 7.5 and Section 7.6.





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   When present, public keys and certificates SHOULD be included as ASB
   parameters rather than within ASB results.  This provides size
   efficiency when multiple security results are present because they
   will all be from the same security source and likely share the same
   public key material.  Security acceptors SHALL still process public
   keys or certificates present in a result as applying to that
   individual result.

   Security acceptors SHALL aggregate all public keys from all
   parameters within a single BIB or BCB, independent of encoded type or
   order of parameters.  Because each context contains a single set of
   security parameters which apply to all results in the same context,
   security acceptors SHALL treat all public keys as being related to
   the security source itself and potentially applying to every result.

4.3.1.  PKIX Certificates

   When PKIX certificates are present as parameters, security sources
   SHOULD include the entire certification chain to the root CA.  When
   PKIX certificates are used by security acceptors and the end-entity
   certificate is not explicitly trusted (i.e. pinned), the security
   acceptor SHALL perform the certification path validation of [RFC5280]
   up to one or more trusted CA certificates.  Leaving out part of the
   certification chain can cause the security acceptor to fail to
   validate a BIB if the left-out certificates are unknown to the
   acceptor (see Section 7.6).

   The end entity certificate associated with a BPSec security source
   SHALL adhere to the profile of Section 5.

5.  PKIX Certificate Profile

   All end-entity certificates used for BPSec SHALL conform to
   [RFC5280], or any updates or successors to that profile.

   This profile requires Version 3 certificates due to the extensions
   used by this profile.  Security acceptors SHALL reject as invalid
   Version 1 and Version 2 end-entity certificates.

   Security acceptors SHALL accept certificates that contain an empty
   Subject field or contain a Subject without a Common Name.  Identity
   information in end-entity certificates is contained entirely in the
   subjectAltName extension as a NODE-ID, as defined in
   [I-D.ietf-dtn-tcpclv4].

   All end-entity and CA certificates used for BPSec SHOULD contain both
   a Subject Key Identifier and an Authority Key Identifier extension in
   accordance with [RFC5280].  Security acceptors SHOULD NOT rely on



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   either a Subject Key Identifier and an Authority Key Identifier being
   present in any received certificate.  Including key identifiers
   simplifies the work of an entity needing to assemble a certification
   chain.

   A BPSec end-entity certificate SHALL contain a NODE-ID which
   authenticates the Node ID of the security source.  The identifier
   type NODE-ID is defined in [I-D.ietf-dtn-tcpclv4].

   When allowed by CA policy, a BPSec end-entity certificate SHOULD
   contain a PKIX Extended Key Usage extension in accordance with
   Section 4.2.1.12 of [RFC5280].  When the PKIX Extended Key Usage
   extension is present, it SHALL contain a key purpose "id-kp-
   bundleSecurity" as defined in [I-D.ietf-dtn-tcpclv4].  The "id-kp-
   bundleSecurity" purpose MAY be combined with other purposes in the
   same certificate.

   When allowed by CA policy, a BPSec end-entity certificate SHALL
   contain a PKIX Key Usage extension in accordance with Section 4.2.1.3
   of [RFC5280].  The PKIX Key Usage bits which are consistent with COSE
   security are: digitalSignature, nonRepudiation, keyEncipherment, and
   keyAgreement.  The specific algorithms used by COSE messages in
   security results determine which of those key uses are exercised.
   See Section 5.1 for discussion of key use policies across multiple
   certificates.

   A BPSec end-entity certificate MAY contain an Online Certificate
   Status Protocol (OCSP) URI within an Authority Information Access
   extension in accordance with Section 4.2.2.1 of [RFC5280].  Security
   acceptors are not expected to have continuous internet connectivity
   sufficient to perform OCSP verification.

5.1.  Multiple-Certificate Uses

   A RECOMMENDED security policy is to limit asymmetric keys (and thus
   public key certificates) to single uses among the following:

   Bundle transport:  With key uses as defined in the convergence layer
      specification(s).

   Block signing:  With key use digitalSignature and/or nonRepudiation

   Block encryption:  With key use keyEncipherment and/or keyAgreement








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   This policy is the same one recommended by Section 6 of [RFC8551] for
   email security and by Section 5.2 of [NIST-SP800-57] more generally.
   Effectively this means that a BP node uses separate certificates for
   transport (e.g., as a TCPCL entity), BIB signing (as a security
   source), and BCB encryption (as a security acceptor).

6.  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.

7.  Security Considerations

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

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

7.1.  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



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   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.

7.2.  Threat: Untrusted End-Entity Certificate

   The profile in Section 3.6.1 uses end-entity certificates chained up
   to a trusted root CA.  A security source can include a certificate
   set which does not contain the full chain, possibly excluding
   intermediate or root CAs.  In an environment where security acceptors
   are known to already contain needed root and intermediate CAs there
   is no need to include those CAs, but this has a risk of an acceptor
   not actually having one of the needed CAs.

7.3.  Threat: Certificate Validation Vulnerabilities

   Even when a security acceptor is operating properly an attacker can
   attempt to exploit vulnerabilities within certificate check
   algorithms or configuration to authenticate using an invalid
   certificate.  An invalid certificate exploit could lead to higher-
   level security issues and/or denial of service to the Node ID being
   impersonated.

   There are many reasons, described in [RFC5280] and [RFC6125], why a
   certificate can fail to validate, including using the certificate
   outside of its valid time interval, using purposes for which it was
   not authorized, or using it after it has been revoked by its CA.
   Validating a certificate is a complex task and can require network
   connectivity outside of the primary BP convergence layer network
   path(s) if a mechanism such as OCSP [RFC6960] is used by the CA.  The
   configuration and use of particular certificate validation methods
   are outside of the scope of this document.

7.4.  Threat: BP Node Impersonation

   When certificates are referenced by BIB results it is possible that
   the certificate does not contain a NODE-ID or does contain one but
   has a mismatch with the actual security source (see Section 1.2).
   Having a CA-validated certificate does not alone guarantee the
   identity of the security source from which the certificate is
   provided; additional validation procedures in Section 4.3.1 bind the
   Node ID based on the contents of the certificate.




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7.5.  Threat: Unidentifiable Key

   The profile in Section 4.2 recommends key identifiers when possible
   and the parameters in section Section 3.2 allow encoding public keys
   where available.  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.

   Because the key identifier headers are unprotected (see Section 4.3),
   there is still the possibility that an active attacker removes or
   alters key identifier(s) in the result.  This can cause the security
   acceptor to not be able to properly verify a valid signature or not
   use the correct private key to decrypt valid ciphertext.

7.6.  Threat: Non-Trusted Public Key

   The profile in Section 4.2 allows the use of PKIX which typically
   involves end-entity certificates chained up to a trusted root CA.
   This allows a BIB to contain end-entity certificates not previously
   known to a security acceptor but still trust the certificate by
   verifying it up to a trusted CA.  In an environment where security
   acceptors are known to already contain needed root and intermediate
   CAs there is no need to include those CAs in a proper chain within
   the security parameters, but this has a risk of an acceptor not
   actually having one of the needed CAs.

   Because the security parameters are not included as AAD, there is
   still the possibility that an active attacker removes or alters
   certification chain data in the parameters.  This can cause the
   security acceptor to be able to verify a valid signature but not
   trust the public key used to perform the verification.

7.7.  Threat: Passive Leak of Key Material

   It is important that the key requirements of Section 3.2 apply only
   to public keys and PKIX certificates.  Including non-public key
   material in ASB parameters will expose that material in the bundle
   data and over the bundle convergence layer during transport.









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7.8.  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].

8.  IANA Considerations

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

8.1.  BPSec Security Contexts

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

             +==========+=============+=====================+
             | Value    | Description | Reference           |
             +==========+=============+=====================+
             | TBD-COSE | COSE        | This specification. |
             +----------+-------------+---------------------+

                                 Table 6

9.  Acknowledgments

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

10.  References

10.1.  Normative References

   [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>.




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   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6960]  Santesson, S., Myers, M., Ankney, R., Malpani, A.,
              Galperin, S., and C. Adams, "X.509 Internet Public Key
              Infrastructure Online Certificate Status Protocol - OCSP",
              RFC 6960, DOI 10.17487/RFC6960, June 2013,
              <https://www.rfc-editor.org/info/rfc6960>.

   [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>.

   [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>.

   [RFC8551]  Schaad, J., Ramsdell, B., and S. Turner, "Secure/
              Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
              Message Specification", RFC 8551, DOI 10.17487/RFC8551,
              April 2019, <https://www.rfc-editor.org/info/rfc8551>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.




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   [I-D.ietf-dtn-bpsec]
              Birrane, E. and K. McKeever, "Bundle Protocol Security
              Specification", Work in Progress, Internet-Draft, draft-
              ietf-dtn-bpsec-25, 1 December 2020,
              <https://tools.ietf.org/html/draft-ietf-dtn-bpsec-25>.

   [I-D.ietf-dtn-tcpclv4]
              Sipos, B., Demmer, M., Ott, J., and S. Perreault, "Delay-
              Tolerant Networking TCP Convergence Layer Protocol Version
              4", Work in Progress, Internet-Draft, draft-ietf-dtn-
              tcpclv4-24, 7 December 2020,
              <https://tools.ietf.org/html/draft-ietf-dtn-tcpclv4-24>.

   [I-D.ietf-cose-x509]
              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Header parameters for carrying and referencing X.509
              certificates", Work in Progress, Internet-Draft, draft-
              ietf-cose-x509-08, 14 December 2020,
              <https://tools.ietf.org/html/draft-ietf-cose-x509-08>.

10.2.  Informative References

   [NIST-SP800-57]
              National Institute of Standards and Technology,
              "Recommendation for Key Management - Part 1: General",
              NIST Special Publication 800-57 Revision 4, DOI 10.6028/
              NIST.SP.800-57pt1r5, May 2020,
              <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
              NIST.SP.800-57pt1r5.pdf>.

   [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>.

   [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>.

   [I-D.ietf-dtn-bpbis]
              Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol
              Version 7", Work in Progress, Internet-Draft, draft-ietf-
              dtn-bpbis-30, 10 December 2020,
              <https://tools.ietf.org/html/draft-ietf-dtn-bpbis-30>.






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   [I-D.ietf-dtn-bpsec-interop-sc]
              Birrane, E., "BPSec Default Security Contexts", Work in
              Progress, Internet-Draft, draft-ietf-dtn-bpsec-interop-sc-
              02, 1 November 2020, <https://tools.ietf.org/html/draft-
              ietf-dtn-bpsec-interop-sc-02>.

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

Appendix A.  Examples

   These examples are intended to have the correct structure of COSE
   security blocks but in some cases use simplified algorithm parameters
   or smaller key sizes than are required by the actual COSE profile
   defined in this documents.  Each example indicates how it differs
   from the actual profile if there is a meaningful difference.

   All of these examples operate within the context of the bundle
   primary block of Figure 5 with a security target block of Figure 6.
   All example figures use the extended diagnostic notation [RFC8610].

   [
     7, / BP version /
     0, / flags /
     0, / CRC type /
     [1, "//dst/svc"], / 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 /
     <<300>> / type-specific-data: age /
   ]

                   Figure 6: Target block CBOR diagnostic






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   All of the examples also operate within a security block containing
   the AAD Scope parameter with only "has-primary-ctx" and "has-target-
   ctx" flags set.  This results in a consistent AAD-value as shown in
   Figure 7, which is used as the bytestring for COSE external_aad in
   all of the examples.  Note that the AAD-value is itself a bytestring
   which happens to contain encoded CBOR.

   <<[
     [ 7, 0, 0, [ 1, "//dst/svc" ], [ 1, "//src/" ], [ 1, "//src/" ],
       [ 0, 40 ], 1000000 ], / primary-ctx /
     [ 7, 2, 0 ], / target-ctx /
     null / security-ctx /
   ]>>

             Figure 7: Example scope AAD-value CBOR diagnostic

   The only differences between these examples which use EC or RSA
   keypairs and a use of a PKIX public key certificate are: the
   parameters would have an x5chain parameter instead of a COSE_Key
   type, and the recipient would contain an "x5t" value instead of a
   "kid" value.  Neither of these is a change to a protected header so,
   given the same private key, there would be no change to the signature
   or wrapped-key data.

A.1.  Symmetric Key COSE_Mac0

   This is an example of a MAC with recipient having a 256-bit symmetric
   key identified by a "kid".

   [
     {
       / kty / 1: 4, / symmetric /
       / kid / 2: 'ExampleMAC',
       / k / -1: h'13bf9cead057c0aca2c9e52471ca4b19ddfaf4c0784e3f3e8e39
   99dbae4ce45c'
     }
   ]

                          Figure 8: Symmetric Key

   The external_aad is the encoded data from Figure 7.  The payload is
   the encoded target block-type-specific data from Figure 6.









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   [
     "MAC0", / context /
     h'a10105', / protected /
     h'83880700008201692f2f6473742f7376638201662f2f7372632f8201662f2f73
   72632f820018281a000f424083070200f6', / external_aad /
     h'19012c' / payload /
   ]

                  Figure 9: MAC_structure CBOR diagnostic

   [
     [2], / targets /
     0, / security context TBD /
     1, / flags: params-present /
     [ / parameters /
       [
         5, / AAD-scope /
         0x03 / has-primary-ctx | has-target-ctx /
       ]
     ],
     [
       [ / target block #2 /
         [ / result /
           17, / COSE_Mac0 tag /
           [
             <<{ / protected /
                / alg / 1:5 / HMAC 256//256 /
             }>>,
             { / unprotected /
               / kid / 4:'ExampleMAC'
             },
             null, / payload /
             h'190264a1e6a9734990e552660df3c4641efb88fd6439aba866577c7b
   6d174b87' / tag /
           ]
         ]
       ]
     ]
   ]

             Figure 10: Abstract Security Block CBOR diagnostic

A.2.  EC Keypair COSE_Sign1

   This is an example of a signature with a recipient having a P-256
   curve EC keypair identified by a "kid".  The associated public key is
   included as a security parameter.




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   [
     { / signing private key /
       / kty / 1: 2, / EC2 /
       / kid / 2: 'ExampleEC2',
       / crv / -1: 1, / P-256 /
       / x / -2: h'44c1fa63b84f172b50541339c50beb0e630241ecb4eebbddb8b5
   e4fe0a1787a8',
       / y / -3: h'059451c7630d95d0b550acbd02e979b3f4f74e645b74715fafbc
   1639960a0c7a',
       / d / -4: h'dd6e7d8c4c0e0c0bd3ae1b4a2fa86b9a09b7efee4a233772cf51
   89786ea63842'
     }
   ]

                          Figure 11: Example Keys

   The external_aad is the encoded data from Figure 7.  The payload is
   the encoded target block-type-specific data from Figure 6.

   [
     "Signature1", / context /
     h'a10126', / protected /
     h'83880700008201692f2f6473742f7376638201662f2f7372632f8201662f2f73
   72632f820018281a000f424083070200f6', / external_aad /
     h'19012c' / payload /
   ]

                  Figure 12: Sig_structure CBOR diagnostic























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   [
     [2], / targets /
     0, / security context TBD /
     1, / flags: params-present /
     [ / parameters /
       [
         1, / COSE key /
         { / public key /
           / kty / 1: 2, / EC2 /
           / kid / 2: 'ExampleEC2',
           / crv / -1: 1, / P-256 /
           / x / -2: h'44c1fa63b84f172b50541339c50beb0e630241ecb4eebbdd
   b8b5e4fe0a1787a8',
           / y / -3: h'059451c7630d95d0b550acbd02e979b3f4f74e645b74715f
   afbc1639960a0c7a'
         }
       ],
       [
         5, / AAD-scope /
         0x03 / has-primary-ctx | has-target-ctx /
       ]
     ],
     [
       [ / target block #2 /
         [ / result /
           18, / COSE_Sign1 tag /
           [
             <<{ / protected /
                / alg / 1:-7 / ES256 /
             }>>,
             { / unprotected /
               / kid / 4:'ExampleEC2'
             },
             null, / payload /
             h'eb085c162bac4ec45c974766b897ee227b189fa257a8fb195c830f04
   f6d6a90318b3e915938e4d32c1baace8aa0bf983f52efcbf1b127b296e72673f3d73
   3023' / signature /
           ]
         ]
       ]
     ]
   ]

             Figure 13: Abstract Security Block CBOR diagnostic







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A.3.  RSA Keypair COSE_Sign1

   This is an example of a signature with a recipient having a 1024-bit
   RSA keypair identified by a "kid".  The associated public key is
   included as a security parameter.

   This key strength is not supposed to be a secure configuration, only
   intended to explain the procedure.  This signature uses a random
   salt, so the full signature output is not deterministic.

   [
     { / signing private key /
       / kty / 1: 3, / RSA /
       / kid / 2: 'ExampleRSA',
       / n / -1: h'b0b5fd85f52c91844007443c9f9371980025f76d51fc9c676812
   31da610cb291ba637ce813bffdb2e9c653258607389ec97dad3db295fded67744ed6
   20707db36804e74e56a494030a73608fc8d92f2f0578d2d85cc201ef0ff22d7835d2
   d147d3b90a6884276235a01c2be99dfc597f79554362fc1eb03639cac5ccaddb29
   25',
       / e / -2: h'010001',
       / d / -3: h'9b5d26ad6445ef1aab80b809e4f329684e9912d556c4166f041d
   1b1fb93c04b4037ffd0dbe6f8a8a86e70bab6e0f6344983a9ada27ed9ff7de816fde
   eb5e7be48e607ce5fda4581ca6338a9e019fb3689b28934192b6a190cdda910abb5a
   86a2f7b6f9cd5011049d8de52ddfef73aa06df401c55623ec196720f54920deb4f
   01',
       / p / -4: h'db22d94e7784a27b568cbf985307ea8d6430ff6b88c18a7086fd
   4f57a326572f2250c39e48a6f8e2201661c2dfe12c7386835b649714d050aa36123e
   c3d00e75',
       / q / -5: h'ce7016adc5f326b7520397c5978ee2f50e69279983d54c5d76f0
   5bcd61de0879d7056c923540dff9cbae95dcc0e5e86b52b3c902dc9669c8021c6955
   7effb9f1',
       / dP / -6: h'6a6fcaccea106a3b2e16bf18e57b7ad9a2488a4758ed68a8af6
   86a194f0d585b7477760c738d6665aee0302bcf4237ad0530d83b4b86b887f5a4bdc
   7eea427e1',
       / dQ / -7: h'28a4cae245b1dcb285142e027a1768b9c4af915b59285a93a04
   22c60e05edd9e57663afd023d169bd0ad3bd62da8563d231840802ebbf271ad70b89
   05ba3af91',
       / qInv / -8: h'07b5a61733896270a6bd2bb1654194c54e2bc0e061b543a4e
   d9fa73c4bc79c87148aa92a451c4ab8262b6377a9c7b97f869160ca6f5d853ee4b65
   f4f92865ca3'
     }
   ]

                          Figure 14: Example Keys

   The external_aad is the encoded data from Figure 7.  The payload is
   the encoded target block-type-specific data from Figure 6.




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   [
     "Signature1", / context /
     h'a1013824', / protected /
     h'83880700008201692f2f6473742f7376638201662f2f7372632f8201662f2f73
   72632f820018281a000f424083070200f6', / external_aad /
     h'19012c' / payload /
   ]

                  Figure 15: Sig_structure CBOR diagnostic










































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   [
     [2], / targets /
     0, / security context TBD /
     1, / flags: params-present /
     [ / parameters /
       [
         1, / COSE key /
         { / public key /
           / kty / 1: 3, / RSA /
           / kid / 2: 'ExampleRSA',
           / n / -1: h'b0b5fd85f52c91844007443c9f9371980025f76d51fc9c67
   681231da610cb291ba637ce813bffdb2e9c653258607389ec97dad3db295fded6774
   4ed620707db36804e74e56a494030a73608fc8d92f2f0578d2d85cc201ef0ff22d78
   35d2d147d3b90a6884276235a01c2be99dfc597f79554362fc1eb03639cac5ccaddb
   2925',
           / e / -2: h'010001'
         }
       ],
       [
         5, / AAD-scope /
         0x03 / has-primary-ctx | has-target-ctx /
       ]
     ],
     [
       [ / target block #2 /
         [ / result /
           18, / COSE_Sign1 tag /
           [
             <<{ / protected /
                / alg / 1:-37 / PS256 /
             }>>,
             { / unprotected /
               / kid / 4:'ExampleRSA'
             },
             null, / payload /
             h'2229cec7cd4e77e55b7ef39e0305931527e3075e7cad4969ecf1bdc5
   cb8662435128718c7ba465d2251a770a6c48ddc62f515fca43482ae137fffa67c86b
   c60b3b838875621b276235bdc4269f45fd0c08fdd607650d03ae75b86364f7f5f2cc
   442d60e72bff7939478deba7e3492ea96f8ac1f953583df897138f66c16bc2
   07' / signature /
           ]
         ]
       ]
     ]
   ]

             Figure 16: Abstract Security Block CBOR diagnostic




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A.4.  Symmetric KEK COSE_Encrypt

   This is an example of an encryption with a random CEK and an explicit
   key-encryption key (KEK) identified by a "kid".  The keys used are
   shown in Figure 17.

   [
     {
       / kty / 1: 4, / symmetric /
       / kid / 2: 'ExampleKEK',
       / k / -1: h'0e8a982b921d1086241798032fedc1f883eab72e4e43bb2d11cf
   ae38ad7a972e'
     },
     {
       / kty / 1: 4, / symmetric /
       / kid / 2: 'ExampleCEK',
       / k / -1: h'13bf9cead057c0aca2c9e52471ca4b19ddfaf4c0784e3f3e8e39
   99dbae4ce45c'
     }
   ]

                          Figure 17: Example Keys

   The external_aad is the encoded data from Figure 7.  The payload is
   the encoded target block-type-specific data from Figure 6.

   [
     "Encrypt", / context /
     h'a10103', / protected /
     h'83880700008201692f2f6473742f7376638201662f2f7372632f8201662f2f73
   72632f820018281a000f424083070200f6' / external_aad /
   ]

                  Figure 18: Enc_structure CBOR diagnostic

















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   [
     [2], / targets /
     0, / security context TBD /
     1, / flags: params-present /
     [ / parameters /
       [
         5, / AAD-scope /
         0x03 / has-primary-ctx | has-target-ctx /
       ]
     ],
     [
       [ / target block #2 /
         [ / result /
           96, / COSE_Encrypt tag /
           [
             <<{ / protected /
                / alg / 1:3 / A256GCM /
             }>>,
             { / unprotected /
               / iv / 5: h'6f3093eba5d85143c3dc484a'
             },
             null, / payload /
             [
               [ / recipient /
                 h'', / protected /
                 { / unprotected /
                   / alg / 1:-5, / A256KW /
                   / kid / 4:'ExampleKEK'
                 },
                 h'917f2045e1169502756252bf119a94cdac6a9d8944245b5a9a26
   d403a6331159e3d691a708e9984d' / key-wrapped /
               ]
             ]
           ]
         ]
       ]
     ]
   ]

             Figure 19: Abstract Security Block CBOR diagnostic

   [
     7, / type code - bundle age /
     2, / block num /
     0, / flags /
     0, / CRC type /
     h'63bb162d8ee2e8175cfc340b6df978864907a2' / ciphertext /
   ]



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             Figure 20: Encrypted Target block CBOR diagnostic

A.5.  EC Keypair COSE_Encrypt

   This is an example of an encryption with an P-256 curve ephemeral
   sender keypair and a static recipient keypair identified by a "kid".
   The keys used are shown in Figure 21.

   [
     { / sender ephemeral private key /
       / kty / 1: 2, / EC2 /
       / crv / -1: 1, / P-256 /
       / x / -2: h'fedaba748882050d1bef8ba992911898f554450952070aeb4788
   ca57d1df6bcc',
       / y / -3: h'ceaa8e7ff4751a4f81c70e98f1713378b0bd82a1414a2f493c1c
   9c0670f28d62',
       / d / -4: h'a2e4ed4f2e21842999b0e9ebdaad7465efd5c29bd5761f5c2088
   0f9d9c3b122a'
     },
     { / recipient private key /
       / kty / 1: 2, / EC2 /
       / kid / 2: 'ExampleEC2',
       / crv / -1: 1, / P-256 /
       / x / -2: h'44c1fa63b84f172b50541339c50beb0e630241ecb4eebbddb8b5
   e4fe0a1787a8',
       / y / -3: h'059451c7630d95d0b550acbd02e979b3f4f74e645b74715fafbc
   1639960a0c7a',
       / d / -4: h'dd6e7d8c4c0e0c0bd3ae1b4a2fa86b9a09b7efee4a233772cf51
   89786ea63842'
     },
     {
       / kty / 1: 4, / symmetric /
       / kid / 2: 'ExampleCEK',
       / k / -1: h'13bf9cead057c0aca2c9e52471ca4b19ddfaf4c0784e3f3e8e39
   99dbae4ce45c'
     }
   ]

                          Figure 21: Example Keys

   The external_aad is the encoded data from Figure 7.  The payload is
   the encoded target block-type-specific data from Figure 6.









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   [
     "Encrypt", / context /
     h'a10103', / protected /
     h'83880700008201692f2f6473742f7376638201662f2f7372632f8201662f2f73
   72632f820018281a000f424083070200f6' / external_aad /
   ]

                  Figure 22: Enc_structure CBOR diagnostic

   [
     [2], / targets /
     0, / security context TBD /
     1, / flags: params-present /
     [ / parameters /
       [
         1, / COSE key /
         { / public key /
           / kty / 1: 2, / EC2 /
           / kid / 2: 'ExampleEC2',
           / crv / -1: 1, / P-256 /
           / x / -2: h'44c1fa63b84f172b50541339c50beb0e630241ecb4eebbdd
   b8b5e4fe0a1787a8',
           / y / -3: h'059451c7630d95d0b550acbd02e979b3f4f74e645b74715f
   afbc1639960a0c7a'
         }
       ],
       [
         5, / AAD-scope /
         0x03 / has-primary-ctx | has-target-ctx /
       ]
     ],
     [
       [ / target block #2 /
         [ / result /
           96, / COSE_Encrypt tag /
           [
             <<{ / protected /
                / alg / 1:3 / A256GCM /
             }>>,
             { / unprotected /
               / iv / 5: h'6f3093eba5d85143c3dc484a'
             },
             null, / payload /
             [
               [ / recipient /
                 h'', / protected /
                 { / unprotected /
                   / alg / 1:-31, / ECDH-ES + A256KW /



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                   / kid / 4:'ExampleEC2',
                   / ephemeral key / -1:{
                     1:2,
                     -1:1,
                     -2:h'fedaba748882050d1bef8ba992911898f554450952070
   aeb4788ca57d1df6bcc',
                     -3:h'ceaa8e7ff4751a4f81c70e98f1713378b0bd82a1414a2
   f493c1c9c0670f28d62'
                   },
                   / PartyU nonce / -22:h'e6bd83a5a06841c2ea1dd4eebaaa
   f252'
                 },
                 h'e20b6fd9b46cdaae9e67ccf4893706802a7acb0c3b3a792b3fcb
   a110f2f27d7972934f4e6497ac89' / key-wrapped /
               ]
             ]
           ]
         ]
       ]
     ]
   ]

             Figure 23: Abstract Security Block CBOR diagnostic

   [
     7, / type code - bundle age /
     2, / block num /
     0, / flags /
     0, / CRC type /
     h'63bb162d8ee2e8175cfc340b6df978864907a2' / ciphertext /
   ]

             Figure 24: Encrypted Target block CBOR diagnostic

A.6.  RSA Keypair COSE_Encrypt

   This is an example of an encrypion with a recipient having a 1024-bit
   RSA keypair identified by a "kid".  The associated public key is
   included as a security parameter.

   This key strength is not supposed to be a secure configuration, only
   intended to explain the procedure.  This padding scheme uses a random
   salt, so the full layer-2 ciphertext output is not deterministic.








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   [
     { / recipient private key /
       / kty / 1: 3, / RSA /
       / kid / 2: 'ExampleRSA',
       / n / -1: h'b0b5fd85f52c91844007443c9f9371980025f76d51fc9c676812
   31da610cb291ba637ce813bffdb2e9c653258607389ec97dad3db295fded67744ed6
   20707db36804e74e56a494030a73608fc8d92f2f0578d2d85cc201ef0ff22d7835d2
   d147d3b90a6884276235a01c2be99dfc597f79554362fc1eb03639cac5ccaddb29
   25',
       / e / -2: h'010001',
       / d / -3: h'9b5d26ad6445ef1aab80b809e4f329684e9912d556c4166f041d
   1b1fb93c04b4037ffd0dbe6f8a8a86e70bab6e0f6344983a9ada27ed9ff7de816fde
   eb5e7be48e607ce5fda4581ca6338a9e019fb3689b28934192b6a190cdda910abb5a
   86a2f7b6f9cd5011049d8de52ddfef73aa06df401c55623ec196720f54920deb4f
   01',
       / p / -4: h'db22d94e7784a27b568cbf985307ea8d6430ff6b88c18a7086fd
   4f57a326572f2250c39e48a6f8e2201661c2dfe12c7386835b649714d050aa36123e
   c3d00e75',
       / q / -5: h'ce7016adc5f326b7520397c5978ee2f50e69279983d54c5d76f0
   5bcd61de0879d7056c923540dff9cbae95dcc0e5e86b52b3c902dc9669c8021c6955
   7effb9f1',
       / dP / -6: h'6a6fcaccea106a3b2e16bf18e57b7ad9a2488a4758ed68a8af6
   86a194f0d585b7477760c738d6665aee0302bcf4237ad0530d83b4b86b887f5a4bdc
   7eea427e1',
       / dQ / -7: h'28a4cae245b1dcb285142e027a1768b9c4af915b59285a93a04
   22c60e05edd9e57663afd023d169bd0ad3bd62da8563d231840802ebbf271ad70b89
   05ba3af91',
       / qInv / -8: h'07b5a61733896270a6bd2bb1654194c54e2bc0e061b543a4e
   d9fa73c4bc79c87148aa92a451c4ab8262b6377a9c7b97f869160ca6f5d853ee4b65
   f4f92865ca3'
     },
     {
       / kty / 1: 4, / symmetric /
       / kid / 2: 'ExampleCEK',
       / k / -1: h'13bf9cead057c0aca2c9e52471ca4b19ddfaf4c0784e3f3e8e39
   99dbae4ce45c'
     }
   ]

                          Figure 25: Example Keys

   The external_aad is the encoded data from Figure 7.  The payload is
   the encoded target block-type-specific data from Figure 6.








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   [
     "Encrypt", / context /
     h'a10103', / protected /
     h'83880700008201692f2f6473742f7376638201662f2f7372632f8201662f2f73
   72632f820018281a000f424083070200f6' / external_aad /
   ]

                  Figure 26: Enc_structure CBOR diagnostic

   [
     [2], / targets /
     0, / security context TBD /
     1, / flags: params-present /
     [ / parameters /
       [
         1, / COSE key /
         { / public key /
           / kty / 1: 3, / RSA /
           / kid / 2: 'ExampleRSA',
           / n / -1: h'b0b5fd85f52c91844007443c9f9371980025f76d51fc9c67
   681231da610cb291ba637ce813bffdb2e9c653258607389ec97dad3db295fded6774
   4ed620707db36804e74e56a494030a73608fc8d92f2f0578d2d85cc201ef0ff22d78
   35d2d147d3b90a6884276235a01c2be99dfc597f79554362fc1eb03639cac5ccaddb
   2925',
           / e / -2: h'010001'
         }
       ],
       [
         5, / AAD-scope /
         0x03 / has-primary-ctx | has-target-ctx /
       ]
     ],
     [
       [ / target block #2 /
         [ / result /
           96, / COSE_Encrypt tag /
           [
             <<{ / protected /
                / alg / 1:3 / A256GCM /
             }>>,
             { / unprotected /
               / iv / 5: h'6f3093eba5d85143c3dc484a'
             },
             null, / payload /
             [
               [ / recipient /
                 h'', / protected /
                 { / unprotected /



Sipos                     Expires 25 June 2021                 [Page 38]


Internet-Draft               DTN BPSec COSE                December 2020


                   / alg / 1:-41, / RSAES-OAEP w SHA-256 /
                   / kid / 4:'ExampleRSA'
                 },
                 h'69e76a39b908090f55b1048c95bd1683d9ce702fd9ed4a149650
   72fd411936ade41a36a9f62921635d14406eb0e1fa3c02ca0d957a4a44006aa3c03e
   326867964b166f8731ebcb20d413fd8f26c57c337689dc42235bfd2b928619b0d4f2
   7ec118c608ad9d18c881bc5124833483ded5f5fb079805f3e299fa45f756ecc4c3
   e6' / key-wrapped /
               ]
             ]
           ]
         ]
       ]
     ]
   ]

             Figure 27: Abstract Security Block CBOR diagnostic

   [
     7, / type code - bundle age /
     2, / block num /
     0, / flags /
     0, / CRC type /
     h'63bb162d8ee2e8175cfc340b6df978864907a2' / ciphertext /
   ]

             Figure 28: 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













Sipos                     Expires 25 June 2021                 [Page 39]