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Versions: 00 01

Network Working Group                                          N. Madden
Internet-Draft                                                 ForgeRock
Intended status: Standards Track                            May 10, 2019
Expires: November 11, 2019


         Public Key Authenticated Encryption for JOSE: ECDH-1PU
                     draft-madden-jose-ecdh-1pu-01

Abstract

   This document describes the ECDH-1PU public key authenticated
   encryption algorithm for JWE.  The algorithm is similar to the
   existing ECDH-ES encryption algorithm, but adds an additional ECDH
   key agreement between static keys of the sender and recipient.  This
   additional step allows the recipient to be assured of sender
   authenticity without requiring a nested signed-then-encrypted message
   structure.  The mode is also a useful building block for constructing
   interactive handshake protocols on top of JOSE.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 11, 2019.

Copyright Notice

   Copyright (c) 2019 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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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   3
   2.  Key Agreement with Elliptic Curve Diffie-Hellman One-Pass
       Unified Model (ECDH-1PU)  . . . . . . . . . . . . . . . . . .   3
     2.1.  Header Parameters used for ECDH Key Agreement . . . . . .   4
       2.1.1.  "skid" Header Parameter . . . . . . . . . . . . . . .   5
     2.2.  Key Derivation for ECDH-1PU Key Agreement . . . . . . . .   5
   3.  Two-way interactive handshake . . . . . . . . . . . . . . . .   6
   4.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  JSON Web Signature and Encryption Algorithms Registration   7
       4.1.1.  ECDH-1PU  . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  JSON Web Signature and Encryption Header Parameters
           Registration  . . . . . . . . . . . . . . . . . . . . . .   8
       4.2.1.  skid  . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Example ECDH-1PU Key Agreement Computation with
                A256GCM  . . . . . . . . . . . . . . . . . . . . . .  10
   Appendix B.  Example Interactive Handshake  . . . . . . . . . . .  13
     B.1.  Initial message from Alice to Bob . . . . . . . . . . . .  14
     B.2.  Response message from Bob to Alice  . . . . . . . . . . .  18
   Appendix C.  Document History . . . . . . . . . . . . . . . . . .  21
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   JSON Object Signing and Encryption (JOSE) defines a number of
   encryption (JWE) [RFC7516] and digital signature (JWS) [RFC7515]
   algorithms.  When symmetric cryptography is used, JWE provides
   authenticated encryption that ensures both confidentiality and sender
   authentication.  However, for public key cryptography the existing
   JWE encryption algorithms provide only confidentiality and some level
   of ciphertext integrity.  When sender authentication is required,
   users must resort to nested signed-then-encrypted structures, which
   increases the overhead and size of resulting messages.  This document
   describes an alternative encryption algorithm called ECDH-1PU that
   provides public key authenticated encryption, allowing the benefits
   of authenticated encryption to be enjoyed for public key JWE as it
   currently is for symmetric cryptography.




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   ECDH-1PU is based on the One-Pass Unified Model for Elliptic Curve
   Diffie-Hellman key agreement described in [NIST.800-56A].

   The advantages of public key authenticated encryption with ECDH-1PU
   compared to using nested signed-then-encrypted documents include the
   following:

   o  The resulting message size is more compact as an additional layer
      of headers and base64url-encoding is avoided.  A 500-byte payload
      when encrypted and authenticated with ECDH-1PU (with P-256 keys
      and "A256GCM" Content Encryption Method) results in a 1087-byte
      JWE in Compact Encoding.  An equivalent nested signed-then-
      encrypted JOSE message using the same keys and encryption method
      is 1489 bytes (37% larger).

   o  The same primitives are used for both confidentiality and
      authenticity, providing savings in code size for constrained
      environments.

   o  The generic composition of signatures and public key encryption
      involves a number of subtle details that are essential to security
      [PKAE].  Providing a dedicated algorithm for public key
      authenticated encryption reduces complexity for users of JOSE
      libraries.

   o  ECDH-1PU provides only authenticity and not the stronger security
      properties of non-repudiation or third-party verifiability.  This
      can be an advantage in applications where privacy, anonymity, or
      plausible deniability are goals.

1.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC8174] when, and only when, they appear in all capitals, as
   shown here.

2.  Key Agreement with Elliptic Curve Diffie-Hellman One-Pass Unified
    Model (ECDH-1PU)

   This section defines the specifics of key agreement with Elliptic
   Curve Diffie-Hellman One-Pass Unified Model, in combination with the
   one-step KDF, as defined in Section 5.8.2.1 of [NIST.800-56A] using
   the Concatenation Format of Section 5.8.2.1.1.  This is identical to
   the ConcatKDF function used by the existing JWE ECDH-ES algorithm
   defined in Section 4.6 of [RFC7518].  As for ECDH-ES, the key
   agreement result can be used in one of two ways:



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   1.  directly as the Content Encryption Key (CEK) for the "enc"
       algorithm, in the Direct Key Agreement mode, or

   2.  as a symmetric key used to wrap the CEK with the "A128KW",
       "A192KW", or "A256KW" algorithms, in the Key Agreement with Key
       Wrapping mode.

   A new ephemeral public key value MUST be generated for each key
   agreement operation.

   In Direct Key Agreement mode, the output of the KDF MUST be a key of
   the same length as that used by the "enc" algorithm.  In this case,
   the empty octet sequence is used as the JWE Encrypted Key value.  The
   "alg" (algorithm) Header Parameter value "ECDH-1PU" is used in Direct
   Key Agreement mode.

   In Key Agreement with Key Wrapping mode, the output of the KDF MUST
   be a key of the length needed for the specified key wrapping
   algorithm.  In this case, the JWE Encrypted Key is the CEK wrapped
   with the agreed-upon key.

   The following "alg" (algorithm) Header Parameter values are used to
   indicate the JWE Encrypted Key is the result of encrypting the CEK
   using the result of the key agreement algorithm as the key encryption
   key for the corresponding key wrapping algorithm:

   +-----------------+-------------------------------------------------+
   | "alg" Param     | Key Management Algorithm                        |
   | Value           |                                                 |
   +-----------------+-------------------------------------------------+
   | ECDH-1PU+A128KW | ECDH-1PU using one-pass KDF and CEK wrapped     |
   |                 | with "A128KW"                                   |
   | ECDH-1PU+A192KW | ECDH-1PU using one-pass KDF and CEK wrapped     |
   |                 | with "A192KW"                                   |
   | ECDH-1PU+A256KW | ECDH-1PU using one-pass KDF and CEK wrapped     |
   |                 | with "A256KW"                                   |
   +-----------------+-------------------------------------------------+

2.1.  Header Parameters used for ECDH Key Agreement

   The "epk" (ephemeral public key), "apu" (Agreement PartyUInfo), and
   "apv" (Agreement PartyVInfo) header parameters are used in ECDH-1PU
   exactly as defined in Section 4.6.1 of [RFC7518].

   When no other values are supplied, it is RECOMMENDED that the
   producer software initializes the "apu" header to the base64url-
   encoding of the SHA-256 hash of the concatenation of the sender's
   static public key and the ephemeral public key, and the "apv" header



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   to the base64url-encoding of the SHA-256 hash of the recipient's
   static public key.  This ensures that all keys involved in the key
   agreement are cryptographically bound to the derived keys.

2.1.1.  "skid" Header Parameter

   A new Header Parameter "skid" (Sender Key ID) is registered as a hint
   as to which of the sender's keys was used to authenticate the JWE.
   The structure of the "skid" value is unspecified.  Its value MUST be
   a case-sensitive string.  Use of this Header Parameter is OPTIONAL.
   When used with a JWK, the "skid" value is used to match a JWK "kid"
   parameter value.

2.2.  Key Derivation for ECDH-1PU Key Agreement

   The key derivation process derives the agreed-upon key from the
   shared secret Z established through the ECDH algorithm, per
   Section 6.2.1.2 of [NIST.800-56A].  For the NIST prime order curves
   "P-256", "P-384", and "P-521", the ECC CDH primitive for cofactor
   Diffie-Hellman defined in Section 5.7.1.2 of [NIST.800-56A] is used
   (taking note that the cofactor for all these curves is 1).  For
   curves "X25519" and "X448" the appropriate ECDH primitive from
   Section 5 of [RFC7748] is used.

   Key derivation is performed using the one-step KDF, as defined in
   Section 5.8.1 and Section 5.8.2.1 of [NIST.800-56A] using the
   Concatenation Format of Section 5.8.2.1.1, where the Auxilary
   Function H is SHA-256.  The KDF parameters are set as follows:

   Z  This is set to the representation of the shared secret Z as an
      octet sequence.  As per Section 6.2.1.2 of [NIST.800-56A] Z is the
      concatenation of Ze and Zs, where Ze is the shared secret derived
      from applying the ECDH primitive to the sender's ephemeral private
      key and the recipient's static public key.  Zs is the shared
      secret derived from applying the ECDH primitive to the sender's
      static private key and the recipient's static public key.

   keydatalen  This is set to the number of bits in the desired output
      key.  For "ECDH-1PU", this is the length of the key used by the
      "enc" algorithm.  For "ECDH-1PU+A128KW", "ECDH-1PU+A192KW", and
      "ECDH-1PU+A256KW", this is 128, 192, and 256, respectively.

   AlgorithmID  The AlgorithmID values is of the form Datalen || Data,
      where Data is a variable-length string of zero or more octets, and
      Datalen is a fixed-length, big-endian 32-bit counter that
      indicates the length (in octets) of Data.  In the Direct Key
      Agreement case, Data is set to the octets of the ASCII
      representation of the "enc" Header Parameter value.  In the Key



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      Agreement with Key Wrapping case, Data is set to the octets of the
      ASCII representation of the "alg" (algorithm) Header Parameter
      value.

   PartyUInfo  The PartyUInfo value is of the form Datalen || Data,
      where Data is a variable-length string of zero or more octets, and
      Datalen is a fixed-length, big-endian 32-bit counter that
      indicates the length (in octets) of Data.  If an "apu" (agreement
      PartyUInfo) Header Parameter is present, Data is set to the result
      of base64url decoding the "apu" value and Datalen is set to the
      number of octets in Data.  Otherwise, Datalen is set to 0 and Data
      is set to the empty octet sequence.

   PartyVInfo  The PartyVInfo value is of the form Datalen || Data,
      where Data is a variable-length string of zero or more octets, and
      Datalen is a fixed-length, big-endian 32-bit counter that
      indicates the length (in octets) of Data.  If an "apv" (agreement
      PartyVInfo) Header Parameter is present, Data is set to the result
      of base64url decoding the "apv" value and Datalen is set to the
      number of octets in Data.  Otherwise, Datalen is set to 0 and Data
      is set to the empty octet sequence.

   SuppPubInfo  This is set to the keydatalen represented as a 32-bit
      big-endian integer.

   SuppPrivInfo  This is set to the empty octet sequence.

   Applications need to specifiy how the "apu" and "apv" Header
   Parameters are used for that application.  The "apu" and "apv" values
   MUST be distinct, when used.  Applications wishing to conform to
   [NIST.800-56A] need to provide values that meet the requirements of
   that doucument, e.g., by using values that identify the producer and
   consumer.

   See Appendix A for an example key agreement computation using this
   method.

3.  Two-way interactive handshake

   A party that has received a JWE encrypted with ECDH-1PU MAY reply to
   that message by creating a new JWE using ECDH-1PU, but using the
   ephemeral public key ("epk") from the first message as if it was the
   originating party's static public key.  In this case, key agreement
   proceeds exactly as for Section 2, but with the originator's
   ephemeral public key used as the recipient (Party V) static public
   key.  The "alg" (algorithm) Header Parameter in the response MUST be
   identical to the "alg" Header Parameter of the original message.  The




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   "enc" (encryption method) Header Parameter in the response MUST also
   be identical to the "enc" Header Parameter of the original message.

   The value of the "apu" (Agreement PartyUInfo) Header Parameter value
   from the original message SHOULD be reflected as the "apv" (Agreement
   PartyVInfo) Header Parameter value in the new message.  Applications
   need to specify how the new "apu" Header Parameter should be
   constructed.

   If a "kid" claim was included in the ephemeral public key of the
   original message, then a "kid" Header Parameter with the same value
   MUST be included in the reply JWE.

   See Appendix B for an example handshake using this method.

   After the initial message and a reply have been exchanged, the two
   parties may communicate using the derived key from the second message
   as the encryption key for any number of additional messages.
   Applications MUST specify the algorithm to be used.  The JWE
   algorithm and encryption method used MUST use the same size key as
   the derived key.  For example, if the derived key is 256-bits, then
   appropriate algorithms include alg=dir and enc=A256GCM, or alg=A256KW
   with any JWE content encryption method.

   If Direct encryption is used, the "enc" (encryption method) of all
   subsequent messages MUST be identical to the "enc" Header Parameter
   of the handshake messages.  If the same derived key is to be used for
   messages in both directions between the two parties, the application
   MUST specify how unique nonces/IVs are to be generated by each party
   to avoid collisions.  It is RECOMMENDED that either a Key Wrap
   algorithm is used, or else the derived key is used as input to a key
   derivation function to derive separate keys for each direction.

4.  IANA considerations

   This section registers identifiers under the IANA JSON Web Signature
   and Encryption Algorithms Registry established by [RFC7518] and the
   IANA JSON Web Signature and Encryption Header Parameters registry
   established by [RFC7515].

4.1.  JSON Web Signature and Encryption Algorithms Registration

   This section registers JWE algorithms as per the registry established
   in [RFC7518].







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4.1.1.  ECDH-1PU

      Algorithm Name: "ECDH-1PU"
      Algorithm Description: ECDH One-Pass Unified Model using one-pass
      KDF
      Algorithm Usage Location(s): "alg"
      JOSE Implementation Requirements: Optional
      Change Controller: IESG
      Specification Document(s): Section 2
      Algorithm Analysis Document(s): [NIST.800-56A] (Section 7.3),
      [PKAE]

4.2.  JSON Web Signature and Encryption Header Parameters Registration

   This section registers new Header Parameters as per the registry
   established in [RFC7515].

4.2.1.  skid

      Header Parameter Name: "skid"
      Header Parameter Description: Sender Key ID
      Header Parameter Usage Location(s): JWE
      Change Controller: IESG
      Specification Document(s): Section 2.1.1

5.  Security Considerations

   The security considerations of [RFC7516] and [RFC7518] relevant to
   ECDH-ES also apply to this specification.

   The security considerations of [NIST.800-56A] apply here.

   When performing an ECDH key agreement between a static private key
   and any untrusted public key, care should be taken to ensure that the
   public key is a valid point on the same curve as the private key.
   Failure to do so may result in compromise of the static private key.
   For the NIST curves P-256, P-384, and P-521, appropriate validation
   routines are given in Section 5.6.2.3.3 of [NIST.800-56A].  For the
   curves used by X25519 and X448, consult the security considerations
   of [RFC7748].

   The ECDH-1PU algorithm is vulnerable to Key Compromise Impersonation
   (KCI) attacks.  If the long-term static private key of a party is
   compromised, then the attacker can not only impersonate that party to
   other parties, but also impersonate any other party when
   communicating with the compromised party.  The second and any
   subsequent messages in the two-way interactive handshake described in
   Section 3 are not vulnerable to KCI.  If resistance to KCI is desired



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   in a single message, then it is RECOMMENDED to use a nested JWS
   signature over the content.

   When Key Agreement with Key Wrapping is used, with the same Content
   Encryption Key (CEK) reused for multiple recipients, any of those
   recipients can produce a new message that appears to come from the
   original sender.  The new message will be indistinguishable from a
   genuine message from the original sender to any of the other
   participants.  The sender SHOULD use a unique CEK for each recipient
   of a message.

   The security properties of the one-pass unified model are given in
   Section 7.3 of [NIST.800-56A].  The ECDH-1PU scheme is also related
   (but not identical) to the "K" one-way handshake pattern of the Noise
   Protocol Framework.  The two-way interactive handshake described in
   Section 3 is also related to the "KK" two-way interactive handshake
   pattern.  The security properties of these handshake patterns are
   given in Section 7.7 of [Noise], although it should be stressed that
   many details differ between Noise and the current specification.

6.  References

6.1.  Normative References

   [NIST.800-56A]
              Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
              Davis, "Recommendation for Pair-Wise Key Establishment
              Using Discrete Logarithm Cryptography Revision 3.", NIST
              Special Publication 800-56A, April 2018.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <https://www.rfc-editor.org/info/rfc7748>.






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   [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>.

6.2.  Informative References

   [Noise]    Perrin, T., "The Noise Protocol Framework, Revision 34",
              July 2018.

   [PKAE]     An, J., "Authenticated Encryption in the Public-Key
              Setting: Security Notions and Analyses", IACR ePrint
              2001/079, 2001.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [RFC8037]  Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH)
              and Signatures in JSON Object Signing and Encryption
              (JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017,
              <https://www.rfc-editor.org/info/rfc8037>.

Appendix A.  Example ECDH-1PU Key Agreement Computation with A256GCM

   This example uses ECDH-1PU in Direct Key Agreement mode ("alg" value
   "ECDH-1PU") to produce an agreed-upon key for AES GCM with a 256-bit
   key ("enc" value "A256GCM").  The example re-uses the keys and
   parameters of the example computation in Appendix C of [RFC7518],
   with the addition of an extra static key-pair for Alice.

   When used in this way, ECDH-1PU has similar security properties to
   the "K" one-way handshake pattern of [Noise], although it is quite
   different in details.

   In this example, a producer Alice is encrypting content to a consumer
   Bob. Alice's static key-pair (in JWK format) used for the key
   agreement in this example (including the private part) is:

         {"kty":"EC",
          "crv":"P-256",
          "x":"WKn-ZIGevcwGIyyrzFoZNBdaq9_TsqzGl96oc0CWuis",
          "y":"y77t-RvAHRKTsSGdIYUfweuOvwrvDD-Q3Hv5J0fSKbE",
          "d":"Hndv7ZZjs_ke8o9zXYo3iq-Yr8SewI5vrqd0pAvEPqg"}

   Bob's static key-pair (in JWK format) is:






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         {"kty":"EC",
          "crv":"P-256",
          "x":"weNJy2HscCSM6AEDTDg04biOvhFhyyWvOHQfeF_PxMQ",
          "y":"e8lnCO-AlStT-NJVX-crhB7QRYhiix03illJOVAOyck",
          "d":"VEmDZpDXXK8p8N0Cndsxs924q6nS1RXFASRl6BfUqdw"}

   The producer (Alice) generates an ephemeral key for the key agreement
   computation.  Alice's ephemeral key (in JWK format) is:

         {"kty":"EC",
          "crv":"P-256",
          "x":"gI0GAILBdu7T53akrFmMyGcsF3n5dO7MmwNBHKW5SV0",
          "y":"SLW_xSffzlPWrHEVI30DHM_4egVwt3NQqeUD7nMFpps",
          "d":"0_NxaRPUMQoAJt50Gz8YiTr8gRTwyEaCumd-MToTmIo"}

   Header Parameter values used in this example are as follows.  The
   "apu" (agreement PartyUInfo) Header Parameter value is the base64url
   encoding of the UTF-8 string "Alice" and the "apv" (agreement
   PartyVInfo) Header Parameter value is the base64url encoding of the
   UTF-8 string "Bob".  The "epk" (ephemeral public key) Header
   Parameter is used to communicate the producer's (Alice's) ephemeral
   public key value to the consumer (Bob).

        {"alg":"ECDH-1PU",
         "enc":"A256GCM",
         "apu":"QWxpY2U",
         "apv":"Qm9i",
         "epk":
          {"kty":"EC",
           "crv":"P-256",
           "x":"gI0GAILBdu7T53akrFmMyGcsF3n5dO7MmwNBHKW5SV0",
           "y":"SLW_xSffzlPWrHEVI30DHM_4egVwt3NQqeUD7nMFpps"
          }
        }

   The resulting one-pass KDF [NIST.800-56A] parameter values are:

   Ze This is set to the output of the ECDH key agreement between
      Alice's ephemeral private key and Bob's static public key.  In
      this example, Ze is the following octet sequence (in hexadecimal
      notation):

         9e 56 d9 1d 81 71 35 d3 72 83 42 83 bf 84 26 9c
         fb 31 6e a3 da 80 6a 48 f6 da a7 79 8c fe 90 c4

   Zs This is set to the output of the ECDH key agreement between
      Alice's static private key and Bob's static public key.  In this




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      example, Zs is the following octet sequence (in hexadecimal
      notation):

         e3 ca 34 74 38 4c 9f 62 b3 0b fd 4c 68 8b 3e 7d
         41 10 a1 b4 ba dc 3c c5 4e f7 b8 12 41 ef d5 0d

   Z  This is set to the concatenation of Ze followed by Zs.  In this
      example, Z is the following octet sequence (in hexadecimal
      notation):

         9e 56 d9 1d 81 71 35 d3 72 83 42 83 bf 84 26 9c
         fb 31 6e a3 da 80 6a 48 f6 da a7 79 8c fe 90 c4
         e3 ca 34 74 38 4c 9f 62 b3 0b fd 4c 68 8b 3e 7d
         41 10 a1 b4 ba dc 3c c5 4e f7 b8 12 41 ef d5 0d

   keydatalen  This value is 256 - the number of bits in the desired
      output key (because "A256GCM" uses a 256-bit key).
   AlgorithmID  This is set to the octets representing the 32-bit big-
      endian value 7 - 00 00 00 07 in hexadecimal notation - the number
      of octets in the AlgorithmID content "A256GCM", followed by the
      octets representing the ASCII string "A256GCM" - 41 32 35 36 47 43
      4d (in hex).  The complete value is therefore: 00 00 00 07 41 32
      35 36 47 43 4d
   PartyUInfo  This is set to the octets representing the 32-bit big-
      endian value 5, followed by the octets representing the UTF-8
      string "Alice".  In hexadecimal notation: 00 00 00 05 41 6c 69 63
      65
   PartyVInfo  This is set to the octets representing the 32-bit big-
      endian value 3, followed by the octets representing the UTF-8
      string "Bob".  In hexadecimal notation: 00 00 00 03 42 6f 62
   SuppPubInfo  This is set to the octets representing the 32-bit big-
      endian value 256 - the keydatalen value.  In hexadecimal notation:
      00 00 01 00
   SuppPrivInfo  This is set to the empty octet sequence.

   Concatenating the parameters AlgorithmID through SuppPrivInfo results
   in a FixedInfo value in Concatenation Format (as per
   Section 5.8.2.1.1 of [NIST.800-56A]) of (in hexidecimal notation):

         00 00 00 07 41 32 35 36 47 43 4d 00 00 00 05 41
         6c 69 63 65 00 00 00 03 42 6f 62 00 00 01 00

   Concatenating the round number 1 (00 00 00 01), Z, and the FixedInfo
   value results in a one-pass KDF round 1 hash input of (hexadecimal):







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         00 00 00 01 9e 56 d9 1d 81 71 35 d3 72 83 42 83
         bf 84 26 9c fb 31 6e a3 da 80 6a 48 f6 da a7 79
         8c fe 90 c4 e3 ca 34 74 38 4c 9f 62 b3 0b fd 4c
         68 8b 3e 7d 41 10 a1 b4 ba dc 3c c5 4e f7 b8 12
         41 ef d5 0d 00 00 00 07 41 32 35 36 47 43 4d 00
         00 00 05 41 6c 69 63 65 00 00 00 03 42 6f 62 00
         00 01 00

   The resulting derived key, which is the full 256 bits of the round 1
   hash output is:

         6c af 13 72 3d 14 85 0a d4 b4 2c d6 dd e9 35 bf
         fd 2f ff 00 a9 ba 70 de 05 c2 03 a5 e1 72 2c a7

   The base64url-encoded representation of this derived key is:

         bK8Tcj0UhQrUtCzW3ek1v_0v_wCpunDeBcIDpeFyLKc

Appendix B.  Example Interactive Handshake

   This example use ECDH-1PU in Direct Key Agreement mode using the X448
   curve from [RFC8037] to perform a two-way interactive handshake.
   When used in this way, ECDH-1PU has similar security properties to
   the "KK" interactive handshake pattern of [Noise].  Messages are
   encrypted using the "A256GCM" encryption method ("enc" Header
   Parameter value).

   In this example, a producer Alice is encrypting content to a consumer
   Bob.  Alice's static key-pair (in JWK format) including the private
   key part is (with linebreaks added for display purposes only):

    {"kty":"OKP",
     "kid":"alice-static",
     "crv": "X448",
     "x":"qaggoGo7qFwBrBtxv4hwI09UaiQmCrF1KdHvaXrzjzzInqDD0Cfx9GlGFi2367
     RATs-hBoB2IHw",
     "d":"hJW9knOYfyCIkZnW922U81uDNNfAwcVeNcpbaQIKyh0iW5LSpDLSmBdPSyvOh7
     J4u9hArU2uoX0"}

   Bob's static key-pair (in JWK format) including the private key part
   is (with linebreaks added for display purposes only):










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    {"kty":"OKP",
     "kid":"bob-static",
     "crv":"X448",
     "x":"4jvO2Ef15DErhV5_5OzoaZDQ2tVb_jHB09eNruOkCTETatzOZ2EGgJCkXNElWR
     sLnbns3TtYYSY",
     "d":"HGKc9R7_Zso3BCnrhzA9GzOzHKHOkMYvb_n54aJ1qkO1qYYTEUS0OQmBZTq1NK
     R5_kmiX5e5r-I"}

B.1.  Initial message from Alice to Bob

   Alice generates an ephemeral key-pair for her handshake with Bob.
   Alice's ephemeral key-pair in JWK format is (with linebreaks added
   for display purposes only):

    {"kty":"OKP",
     "kid":"alice-ephemeral",
     "crv":"X448",
     "x":"6DRxSemaGVx1iVEPRyOAcTKS2zJsi0oZ9bR-IhZUJtezxjSXroVoDTf-RVYBjS
     XdwkLOIGKSI74",
     "d":"8epzr7H0N7ZIIOZeNckLL3iAHfSmIDeb-cMSgI8PJzyQfjZB0tHoGFtkQG7cAK
     xP0Fi6Bbfbe7I"}

   The following JWE Protected Header is used for the message (with line
   breaks and whitespace added for display purposes):

    {"typ":"JWT",
     "epk":{
       "kty":"OKP",
       "crv":"X448",
       "x":"6DRxSemaGVx1iVEPRyOAcTKS2zJsi0oZ9bR-IhZUJtezxjSXroVoDTf-RVYB
       jSXdwkLOIGKSI74"},
     "apv":"Qm9i",
     "apu":"QWxpY2U",
     "kid":"bob-static",
     "enc":"A256GCM",
     "alg":"ECDH-1PU"}

   After removing all whitespace, the octets of ASCII(BASE64URL(UTF8(JWE
   Protected Header))) are as follows (in hexadecimal notation):












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       65 79 4a 30 65 58 41 69 4f 69 4a 4b 56 31 51 69
       4c 43 4a 6c 63 47 73 69 4f 6e 73 69 61 33 52 35
       49 6a 6f 69 54 30 74 51 49 69 77 69 59 33 4a 32
       49 6a 6f 69 57 44 51 30 4f 43 49 73 49 6e 67 69
       4f 69 49 32 52 46 4a 34 55 32 56 74 59 55 64 57
       65 44 46 70 56 6b 56 51 55 6e 6c 50 51 57 4e 55
       53 31 4d 79 65 6b 70 7a 61 54 42 76 57 6a 6c 69
       55 69 31 4a 61 46 70 56 53 6e 52 6c 65 6e 68 71
       55 31 68 79 62 31 5a 76 52 46 52 6d 4c 56 4a 57
       57 55 4a 71 55 31 68 6b 64 32 74 4d 54 30 6c 48
       53 31 4e 4a 4e 7a 51 69 66 53 77 69 59 58 42 32
       49 6a 6f 69 55 57 30 35 61 53 49 73 49 6d 46 77
       64 53 49 36 49 6c 46 58 65 48 42 5a 4d 6c 55 69
       4c 43 4a 72 61 57 51 69 4f 69 4a 69 62 32 49 74
       63 33 52 68 64 47 6c 6a 49 69 77 69 5a 57 35 6a
       49 6a 6f 69 51 54 49 31 4e 6b 64 44 54 53 49 73
       49 6d 46 73 5a 79 49 36 49 6b 56 44 52 45 67 74
       4d 56 42 56 49 6e 30

   The resulting one-pass KDF [NIST.800-56A] parameter values are:

   Ze This is set to the output of the X448 key agreement between
      Alice's ephemeral private key and Bob's static public key.  In
      this example, Ze is the following octet sequence (in hexadecimal
      notation):

       4c b2 b9 11 cd 1c 0a 69 d2 89 4f 39 3b 94 34 29
       61 02 40 f4 19 fc 09 2e bc 06 eb a2 c8 27 17 33
       d2 7d ea 64 c8 b6 4d 66 de c1 db ce 6d de a1 b3
       a5 d3 12 c7 9a 0c e1 47

   Zs This is set to the output of the X448 key agreement between
      Alice's static private key and Bob's static public key.  In this
      example, Zs is the following octet sequence (in hexadecimal
      notation):

       d8 8e aa 18 61 a4 8e a4 69 7b e0 99 c6 bc 3b 73
       4f 0e 13 6d ed e7 75 d3 f3 a2 f4 86 b7 47 ba f0
       e0 39 b1 b6 c1 62 84 07 86 52 0c ff 0c 69 58 db
       ff a5 06 0c 08 5e 77 38

   Z  This is set to the concatenation of Ze followed by Zs.  In this
      example, Z is the following octet sequence (in hexadecimal
      notation):







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       4c b2 b9 11 cd 1c 0a 69 d2 89 4f 39 3b 94 34 29
       61 02 40 f4 19 fc 09 2e bc 06 eb a2 c8 27 17 33
       d2 7d ea 64 c8 b6 4d 66 de c1 db ce 6d de a1 b3
       a5 d3 12 c7 9a 0c e1 47 d8 8e aa 18 61 a4 8e a4
       69 7b e0 99 c6 bc 3b 73 4f 0e 13 6d ed e7 75 d3
       f3 a2 f4 86 b7 47 ba f0 e0 39 b1 b6 c1 62 84 07
       86 52 0c ff 0c 69 58 db ff a5 06 0c 08 5e 77 38

   keydatalen  This value is 256, because "A256GCM" uses a 256-bit key.
   AlgorithmID  This is set to the octets representing the 32-bit big-
      endian value 7 followed by the octets representing the ASCII
      string "A256GCM".  In hexadecimal notation: 00 00 00 07 41 32 35
      36 47 43 4d
   PartyUInfo  This is set to the octets representing the 32-bit big-
      endian value 5 followed by the octets representing the UTF-8
      string "Alice".  In hexadecimal notation: 00 00 00 05 41 6c 69 63
      65
   PartyVInfo  This is set to the octets representing the 32-bit big-
      endian value 3 followed by the octets representing the UTF-8
      string "Bob".  In hexadecimal notation: 00 00 00 03 42 6f 62
   SuppPubInfo  This is set to the octets representing the 32-bit big
      endian value 256 - the keydatalen value.  In hexadecimal: 00 00 01
      00
   SuppPrivInfo  This is set to the empty octet sequence.

   Concatenating the parameters AlgorithmID through SuppPubInfo results
   in a FixedInfo value of (in hex):

       00 00 00 07 41 32 35 36 47 43 4d 00 00 00 05 41
       6c 69 63 65 00 00 00 03 42 6f 62 00 00 01 00

   Concatenating the round number 1 (00 00 00 01), Z, and the FixedInfo
   value results in the KDF round 1 hash input of:

       00 00 00 01 4c b2 b9 11 cd 1c 0a 69 d2 89 4f 39
       3b 94 34 29 61 02 40 f4 19 fc 09 2e bc 06 eb a2
       c8 27 17 33 d2 7d ea 64 c8 b6 4d 66 de c1 db ce
       6d de a1 b3 a5 d3 12 c7 9a 0c e1 47 d8 8e aa 18
       61 a4 8e a4 69 7b e0 99 c6 bc 3b 73 4f 0e 13 6d
       ed e7 75 d3 f3 a2 f4 86 b7 47 ba f0 e0 39 b1 b6
       c1 62 84 07 86 52 0c ff 0c 69 58 db ff a5 06 0c
       08 5e 77 38 00 00 00 07 41 32 35 36 47 43 4d 00
       00 00 05 41 6c 69 63 65 00 00 00 03 42 6f 62 00
       00 01 00

   The resulting derived key, which is the full 256-bits of the round 1
   hash output is:




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       3e 22 44 01 ab cf 8b 1a 93 63 bd 2b 6c 8e 85 c4
       e0 c7 b9 8c ad 3b 51 aa 3f 04 a4 9d 0c 29 da 0c

   Alice then generates a random 96-bit Initialization Vector (IV) for
   A256GCM.  In hexadecimal format:

       3b c5 10 62 97 3c 45 8d 5a 6f 2d 8d

   Alice uses the derived key and the IV to encrypt and authenticate the
   following plaintext JWT Claims Set [RFC7519], with the octets of the
   encoded JWE Protected Header as the Additional Authenticated Data.

       {"msg":"Hello Mike","aud":"Bob","iss":"Alice"}

   In hexadecimal notation, the UTF-8 bytes of this plaintext are:

       7b 22 6d 73 67 22 3a 22 48 65 6c 6c 6f 20 4d 69
       6b 65 22 2c 22 61 75 64 22 3a 22 42 6f 62 22 2c
       22 69 73 73 22 3a 22 41 6c 69 63 65 22 7d

   The resulting Authentication Tag value is:

       4b 39 e8 a7 70 ec eb e3 46 f4 af 77 af 22 4f 42

   The JWE Ciphertext is:

       b5 bd c4 83 44 54 be 02 04 f6 b5 d5 cd 9c 0d f6
       95 57 ab d9 4b ba d4 4f f4 70 0e 57 55 a2 c0 fc
       21 ca 63 56 38 93 7b fb 06 3e 60 f4 a4 cb

   Alice assembles the complete message in JWE Compact Serialization
   format and sends it to Bob (with line breaks added for display
   purposes only):

       eyJ0eXAiOiJKV1QiLCJlcGsiOnsia3R5IjoiT0tQIiwiY3J
       2IjoiWDQ0OCIsIngiOiI2RFJ4U2VtYUdWeDFpVkVQUnlPQW
       NUS1MyekpzaTBvWjliUi1JaFpVSnRlenhqU1hyb1ZvRFRmL
       VJWWUJqU1hkd2tMT0lHS1NJNzQifSwiYXB2IjoiUW05aSIs
       ImFwdSI6IlFXeHBZMlUiLCJraWQiOiJib2Itc3RhdGljIiw
       iZW5jIjoiQTI1NkdDTSIsImFsZyI6IkVDREgtMVBVIn0..O
       8UQYpc8RY1aby2N.tb3Eg0RUvgIE9rXVzZwN9pVXq9lLutR
       P9HAOV1WiwPwhymNWOJN7-wY-YPSkyw.Sznop3Ds6-NG9K9
       3ryJPQg

   The message is 383 octets in size.






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B.2.  Response message from Bob to Alice

   Bob receives the message from Alice and decrypts it, using Alice's
   (known) static public key to authenticate that the message did indeed
   come from Alice.  Bob wishes to establish an interactive secure
   channel with Alice, so replies to her message using the ephemeral key
   from her initial message as Alice's public key.

   Bob generates a fresh ephemeral key-pair of his own.  In this
   example, Bob's ephemeral key-pair (in JWK format) is as follows,
   including the private key parts (with linebreaks added for display
   purposes only):

    {"kty":"OKP",
     "kid":"bob-ephemeral",
     "crv":"X448",
     "x":"_a4lG0EVO62pyVyuGjCIzHYII7vjEBqf02CcNMCHUjWvRMKbkZB-XQ0uzhByXl
     jx0bNgpAvmf84",
     "d":"bNy3py2jvaYOnnzkxV3nOYazDEWTeEOEtTGK7eH-Cjp_m4uCOS-AYqmcUDJCyG
     uFj340p3ld0NA"}

   Bob generates the following JWE Protected Header for his reply to
   Alice (with line breaks and whitespace added for display only):

    {"typ":"JWT",
     "epk":{
       "kty":"OKP",
       "crv":"X448",
       "x":"_a4lG0EVO62pyVyuGjCIzHYII7vjEBqf02CcNMCHUjWvRMKbkZB-XQ0uzhBy
       Xljx0bNgpAvmf84"},
     "apv":"QWxpY2U",
     "apu":"Qm9i",
     "kid":"alice-ephemeral",
     "enc":"A256GCM",
     "alg":"ECDH-1PU"}

   After removing all whitespace, the octets of ASCII(BASE64URL(UTF8(JWE
   Protected Header))) are as follows (in hexadecimal notation):













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       65 79 4a 30 65 58 41 69 4f 69 4a 4b 56 31 51 69
       4c 43 4a 6c 63 47 73 69 4f 6e 73 69 61 33 52 35
       49 6a 6f 69 54 30 74 51 49 69 77 69 59 33 4a 32
       49 6a 6f 69 57 44 51 30 4f 43 49 73 49 6e 67 69
       4f 69 4a 66 59 54 52 73 52 7a 42 46 56 6b 38 32
       4d 6e 42 35 56 6e 6c 31 52 32 70 44 53 58 70 49
       57 55 6c 4a 4e 33 5a 71 52 55 4a 78 5a 6a 41 79
       51 32 4e 4f 54 55 4e 49 56 57 70 58 64 6c 4a 4e
       53 32 4a 72 57 6b 49 74 57 46 45 77 64 58 70 6f
       51 6e 6c 59 62 47 70 34 4d 47 4a 4f 5a 33 42 42
       64 6d 31 6d 4f 44 51 69 66 53 77 69 59 58 42 32
       49 6a 6f 69 55 56 64 34 63 46 6b 79 56 53 49 73
       49 6d 46 77 64 53 49 36 49 6c 46 74 4f 57 6b 69
       4c 43 4a 72 61 57 51 69 4f 69 4a 68 62 47 6c 6a
       5a 53 31 6c 63 47 68 6c 62 57 56 79 59 57 77 69
       4c 43 4a 6c 62 6d 4d 69 4f 69 4a 42 4d 6a 55 32
       52 30 4e 4e 49 69 77 69 59 57 78 6e 49 6a 6f 69
       52 55 4e 45 53 43 30 78 55 46 55 69 66 51 3d 3d

   The resulting KDF parameter values are:

   Ze This is set to the output of the X448 key agreement between Bob's
      ephemeral private key and Alice's ephemeral public key (from the
      first message).  Note that this is an ephemeral-ephemeral key
      agreement.  In hexadecimal notation:

       66 83 28 4e 27 bf 2c e9 02 e1 e1 5d 51 de 25 d7
       86 21 c7 ee 68 21 0e 55 3f c9 3e 9f cd c3 7f f1
       92 b9 c5 35 c2 a2 bc ee bd 03 48 79 82 f9 fb f9
       5b d2 c6 88 c8 5c 05 71

   Zs This is set to the output of the X448 key agreement between Bob's
      static private key and Alice's ephemeral public key from the first
      message.  In hexadecimal notation:

       4c b2 b9 11 cd 1c 0a 69 d2 89 4f 39 3b 94 34 29
       61 02 40 f4 19 fc 09 2e bc 06 eb a2 c8 27 17 33
       d2 7d ea 64 c8 b6 4d 66 de c1 db ce 6d de a1 b3
       a5 d3 12 c7 9a 0c e1 47

   Z  Z is the concatenation of Ze and Zs:










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       66 83 28 4e 27 bf 2c e9 02 e1 e1 5d 51 de 25 d7
       86 21 c7 ee 68 21 0e 55 3f c9 3e 9f cd c3 7f f1
       92 b9 c5 35 c2 a2 bc ee bd 03 48 79 82 f9 fb f9
       5b d2 c6 88 c8 5c 05 71 4c b2 b9 11 cd 1c 0a 69
       d2 89 4f 39 3b 94 34 29 61 02 40 f4 19 fc 09 2e
       bc 06 eb a2 c8 27 17 33 d2 7d ea 64 c8 b6 4d 66
       de c1 db ce 6d de a1 b3 a5 d3 12 c7 9a 0c e1 47

   keydatalen  This is the value 256.
   AlgorithmID  This is set to the octets representing the 32-bit big-
      endian value 7 followed by the octets representing the ASCII
      string "A256GCM".  In hexadecimal notation: 00 00 00 07 41 32 35
      36 47 43 4d
   PartyUInfo  This is set to the octets representing the 32-bit big-
      endian value 3 followed by the octets representing the UTF-8
      string "Bob".  In hexadecimal notation: 00 00 00 03 42 6f 62
   PartyVInfo  Bob echoes back Alice's PartyUInfo as the new PartyVInfo:
      00 00 00 05 41 6c 69 63 65
   SuppPubInfo  This is set to the octets representing the 32-bit big
      endian value 256 - the keydatalen value.  In hexadecimal: 00 00 01
      00
   SuppPrivInfo  This is set to the empty octet sequence.

   Concatenating the parameters AlgorithmID through SuppPubInfo results
   in a FixedInfo value of (in hex):

       00 00 00 07 41 32 35 36 47 43 4d 00 00 00 03 42
       6f 62 00 00 00 05 41 6c 69 63 65 00 00 01 00

   Concatenating the round number 1 (00 00 00 01), Z, and the FixedInfo
   value results in the KDF round 1 hash input of:

       00 00 00 01 66 83 28 4e 27 bf 2c e9 02 e1 e1 5d
       51 de 25 d7 86 21 c7 ee 68 21 0e 55 3f c9 3e 9f
       cd c3 7f f1 92 b9 c5 35 c2 a2 bc ee bd 03 48 79
       82 f9 fb f9 5b d2 c6 88 c8 5c 05 71 4c b2 b9 11
       cd 1c 0a 69 d2 89 4f 39 3b 94 34 29 61 02 40 f4
       19 fc 09 2e bc 06 eb a2 c8 27 17 33 d2 7d ea 64
       c8 b6 4d 66 de c1 db ce 6d de a1 b3 a5 d3 12 c7
       9a 0c e1 47 00 00 00 07 41 32 35 36 47 43 4d 00
       00 00 03 42 6f 62 00 00 00 05 41 6c 69 63 65 00
       00 01 00

   The resulting derived key, which is the full 256-bits of the round 1
   hash output is:

       7c 22 e5 61 29 89 74 7f 4e d3 b1 94 30 e1 7d 3c
       98 14 5c 77 15 5c 71 6a 9d 5d f8 5b ea dd 79 02



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   Bob then generates a random 96-bit IV for A256GCM.  In hexadecimal
   format:

       cd 9f b1 e1 48 cc d8 44 2e 5a a7 49

   Bob uses the derived key and the IV to encrypt and authenticate the
   following plaintext JWT Claims Set, with the octets of the encoded
   JWE Protected Header as the Additional Authenticated Data.

       {"msg":"Hello Joe","aud":"Alice","iss":"Bob"}

   In hexadecimal notation, the UTF-8 bytes of this plaintext are:

       7b 22 6d 73 67 22 3a 22 48 65 6c 6c 6f 20 4a 6f
       65 22 2c 22 61 75 64 22 3a 22 41 6c 69 63 65 22
       2c 22 69 73 73 22 3a 22 42 6f 62 22 7d

   The resulting Authentication Tag value is:

       89 4c a4 f1 a7 7a d0 7b f0 d4 7c da 65 8b d3 95

   The JWE Ciphertext is:

       02 0d 16 b0 17 d4 8e 04 d2 f4 04 17 09 17 6a 6c
       15 57 39 57 c8 ad 16 0c b4 b8 f1 c1 50 18 7d a1
       ef cc b2 d1 da 6b 92 b0 32 bb a1 8b 64

   Bob assembles the complete message in JWE Compact Serialization
   format and sends it to Alice (with line breaks added for display
   purposes only):

       eyJ0eXAiOiJKV1QiLCJlcGsiOnsia3R5IjoiT0tQIiwiY3J
       2IjoiWDQ0OCIsIngiOiJfYTRsRzBFVk82MnB5Vnl1R2pDSX
       pIWUlJN3ZqRUJxZjAyQ2NOTUNIVWpXdlJNS2JrWkItWFEwd
       XpoQnlYbGp4MGJOZ3BBdm1mODQifSwiYXB2IjoiUVd4cFky
       VSIsImFwdSI6IlFtOWkiLCJraWQiOiJhbGljZS1lcGhlbWV
       yYWwiLCJlbmMiOiJBMjU2R0NNIiwiYWxnIjoiRUNESC0xUF
       UifQ..zZ-x4UjM2EQuWqdJ.Ag0WsBfUjgTS9AQXCRdqbBVX
       OVfIrRYMtLjxwVAYfaHvzLLR2muSsDK7oYtk.iUyk8ad60H
       vw1HzaZYvTlQ

Appendix C.  Document History

   -01  Added examples in Appendix A and Appendix B.  Added "skid"
      Header Parameter and registration.  Fleshed out Security
      Considerations.





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Author's Address

   Neil Madden
   ForgeRock
   Broad Quay House
   Prince Street
   Bristol  BS1 4DJ
   United Kingdom

   Email: neil.madden@forgerock.com









































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