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Versions: 00 01 02

(No Working Group)                                           G. Amringer
Internet-Draft                                           January 9, 2020
Intended status: Informational
Expires: July 12, 2020


  Chacha derived AEAD algorithms in JSON Object Signing and Encryption
                                 (JOSE)
                     draft-amringer-jose-chacha-02

Abstract

   This document defines how to use the AEAD algorithms
   "AEAD_XCHACHA20_POLY1305" and "AEAD_CHACHA20_POLY1305" from [RFC8439]
   and [I-D.irtf-cfrg-xchacha] in JSON Object Signing and Encryption
   (JOSE).

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 July 12, 2020.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of
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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.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notation and Conventions  . . . . . . . . . . . . . . . .   2
   2.  Key Encryption  . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Algorithms  . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Header Parameters Used for Key Encryption . . . . . . . .   3
       2.2.1.  "iv" (Initialization Vector) Header Parameter . . . .   3
       2.2.2.  "tag" (Authentication Tag) Header Parameter . . . . .   4
   3.  Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral
       Static  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Content Encryption  . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Algorithms  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Appendix A.  Example using XC20PKW  . . . . . . . . . . . . . . .   7
   Appendix B.  Example using ECDH-ES+XC20PKW  . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The Internet Research Task Force (IRTF) Crypto Forum Research Group
   (CFRG) defined the ChaCha20 and Poly1305 algorithms to be used in
   IETF protocols both independantly and as an AEAD construction
   ([RFC8439]).  It has also been presented with a definition of an
   eXtended-nonce variant ([I-D.irtf-cfrg-xchacha]) for use in stateless
   contexts.  This document defines how to use those algorithms in JOSE
   in an interoperable manner.

   This document defines the conventions to use in the context of
   [RFC7516], and [RFC7517].

1.1.  Notation and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The JOSE key format ("JSON Web Key (JWK)") is defined by [RFC7517]
   and thumbprints for it ("JSON Web Key (JWK) Thumbprint") in
   [RFC7638].








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2.  Key Encryption

2.1.  Algorithms

   This section defines the specifics of encrypting a JWE Content
   Encryption Key (CEK) with AEAD_CHACHA20_POLY1305 [RFC8439] and
   AEAD_XCHACHA20_POLY1305 [I-D.irtf-cfrg-xchacha].

   Use of an Initialization Vector (IV) is REQUIRED with this algorithm.
   The IV is represented in base64url-encoded form as the "iv"
   (initialization vector) Header Parameter value.

   The Additional Authenticated Data value used is the empty octet
   string.

   The JWE Encrypted Key value is the ciphertext output.

   The Authentication Tag output is represented in base64url-encoded
   form as the "tag" (authentication tag) Header Parameter value.

   The following "alg" (algorithm) Header Parameter values are used to
   indicate that the JWE Encrypted Key is the result of encrypting the
   CEK using the corresponding algorithm and IV size:

           +-------------------------+----------+-------------+
           |        Algorithm        | IV size  | "alg" value |
           +-------------------------+----------+-------------+
           |  AEAD_CHACHA20_POLY1305 | 96 bits  |    C20PKW   |
           | AEAD_XCHACHA20_POLY1305 | 192 bits |   XC20PKW   |
           +-------------------------+----------+-------------+

2.2.  Header Parameters Used for Key Encryption

   The following Header Parameters are used for both algorithms defined
   for key encryption.

2.2.1.  "iv" (Initialization Vector) Header Parameter

   The "iv" (initialization vector) Header Parameter value is the
   base64url-encoded representation of the 96-bit or 192-bit IV value
   used for the key encryption operation.  This Header Parameter MUST be
   present and MUST be understood and processed by implementations when
   these algorithms are used.








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2.2.2.  "tag" (Authentication Tag) Header Parameter

   The "tag" (authentication tag) Header Parameter value is the
   base64url-encoded representation of the 128-bit Authentication Tag
   value resulting from the key encryption operation.  This Header
   Parameter MUST be present and MUST be understood and processed by
   implementations when these algorithms are used.

3.  Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static

   This section defines the specifics of key agreement with Elliptic
   Curve Diffie-Hellman Ephemeral Static [RFC6090], in combination with
   the Concat KDF, as defined in Section 5.8.2.1 of NIST.800-56A [1] for
   use as a symmetric key to wrap the CEK with the "C20PKW", or
   "XC20PKW" algorithms, in the Key Agreement with Key Wrapping mode.

   This mode is used exactly as defined in Section 4.6 of RFC7518 [2],
   except that the combined key wrapping algorithms are the ones
   indicated in this document.  All headers pertaining to both the ECDH-
   ES and key wrapping components ("iv",' "tag", "epk", "apu", "apv")
   have the same meaning and requirement as in their original
   definitions.

   The following "alg" (algorithm) Header Parameter values are used to
   indicate that the JWE Encrypted Key is the result of encrypting the
   CEK using the corresponding algorithm:

   +-----------------+-------------------------------------------------+
   |   "alg" value   |             Key Management Algorithm            |
   +-----------------+-------------------------------------------------+
   |  ECDH-ES+C20PKW |  ECDH-ES using Concat KDF and CEK wrapped with  |
   |                 |                      C20PKW                     |
   | ECDH-ES+XC20PKW |  ECDH-ES using Concat KDF and CEK wrapped with  |
   |                 |                     XC20PKW                     |
   +-----------------+-------------------------------------------------+

4.  Content Encryption

4.1.  Algorithms

   This section defines the specifics of performing authenticated
   encryption with ChaCha20-Poly1305.

   The CEK is used as the encryption key.

   Use of an IV is REQUIRED with this algorithm.





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   The following "enc" (encryption algorithm) Header Parameter values
   are used to indicate that the JWE Ciphertext and JWE Authentication
   Tag values have been computed using the corresponding algorithm and
   IV size:

           +-------------------------+----------+-------------+
           |        Algorithm        | IV size  | "alg" value |
           +-------------------------+----------+-------------+
           |  AEAD_CHACHA20_POLY1305 | 96 bits  |     C20P    |
           | AEAD_XCHACHA20_POLY1305 | 192 bits |    XC20P    |
           +-------------------------+----------+-------------+

5.  IANA Considerations

   The following is added to the "JSON Web Signature and Encryption
   Algorithms" registry:

   o Algorithm Name: "C20PKW"
   o Algorithm Description: Key wrapping with ChaCha20-Poly1305
   o Algorithm Usage Location(s): "alg"
   o JOSE Implementation Requirements: Optional
   o Change Controller: IESG
   o Specification Document(s): Section 2 of [RFC-THIS]
   o Algorithm Analysis Documents(s): [RFC8439]

   o Algorithm Name: "XC20PKW"
   o Algorithm Description: Key wrapping with XChaCha20-Poly1305
   o Algorithm Usage Location(s): "alg"
   o JOSE Implementation Requirements: Optional
   o Change Controller: IESG
   o Specification Document(s): Section 2 of [RFC-THIS]
   o Algorithm Analysis Documents(s): [I-D.irtf-cfrg-xchacha]

   o Algorithm Name: "ECDH-ES+C20PKW"
   o Algorithm Description: ECDH-ES using Concat KDF and "C20PKW"
   wrapping
   o Algorithm Usage Location(s): "alg"
   o JOSE Implementation Requirements: Optional
   o Change Controller: IESG
   o Specification Document(s): Section 3 of [RFC-THIS]
   o Algorithm Analysis Documents(s): n/a

   o Algorithm Name: "ECDH-ES+XC20PKW"
   o Algorithm Description: ECDH-ES using Concat KDF and "XC20PKW"
   wrapping
   o Algorithm Usage Location(s): "alg"
   o JOSE Implementation Requirements: Optional
   o Change Controller: IESG



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   o Specification Document(s): Section 3 of [RFC-THIS]
   o Algorithm Analysis Documents(s): n/a

   o Algorithm Name: "C20P"
   o Algorithm Description: ChaCha20-Poly1305
   o Algorithm Usage Location(s): "enc"
   o JOSE Implementation Requirements: Optional
   o Change Controller: IESG
   o Specification Document(s): Section 4 of [RFC-THIS]
   o Algorithm Analysis Documents(s): [RFC8439]

   o Algorithm Name: "XC20P"
   o Algorithm Description: ChaCha20-Poly1305
   o Algorithm Usage Location(s): "enc"
   o JOSE Implementation Requirements: Optional
   o Change Controller: IESG
   o Specification Document(s): Section 4 of [RFC-THIS]
   o Algorithm Analysis Documents(s): [I-D.irtf-cfrg-xchacha]

6.  References

6.1.  Normative References

   [I-D.irtf-cfrg-xchacha]
              Arciszewski, S., "XChaCha: eXtended-nonce ChaCha and
              AEAD_XChaCha20_Poly1305", draft-irtf-cfrg-xchacha-01 (work
              in progress), July 2019.

   [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>.

   [RFC6090]  McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
              Curve Cryptography Algorithms", RFC 6090,
              DOI 10.17487/RFC6090, February 2011,
              <https://www.rfc-editor.org/info/rfc6090>.

   [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>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/info/rfc7517>.






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   [RFC7638]  Jones, M. and N. Sakimura, "JSON Web Key (JWK)
              Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
              2015, <https://www.rfc-editor.org/info/rfc7638>.

   [RFC8439]  Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
              Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018,
              <https://www.rfc-editor.org/info/rfc8439>.

6.2.  URIs

   [1] https://csrc.nist.gov/publications/detail/sp/800-56a/rev-3/final

   [2] https://tools.ietf.org/html/rfc7518#section-4.6

Appendix A.  Example using XC20PKW

   *Considering the payload of "Hello World!"  (Base64URL):*

                             SGVsbG8gV29ybGQh

   *We begin by generating the XChacha20-Poly1309 content encryption key
   (Base64URL):*

                la2knCeFPAvUE2IVPm-RNrwj4UrHffLU6Y1tx3d5T1Q

   *We follow by encrypting the CEK using XChacha20-Poly1309 itself.  We
   generate a new key and a nonce:*

   KEK (Base64URL)

                Rpv7sxPJYeNjKr-L8gPrKtQLHX-1dDuqtJuriVQ0eUY

   Nonce (Base64URL)

                     LuNNS5RAagkOQVewQOLRp9noXET_YsPX

   *Using those parameters, we end up with the following output from
   XChacha20-Poly1309:*

   Ciphertext (Base64URL)

                             K-kXEFjmSsjKzU91

   Tag (Base64URL)

                          VT2Z9a93JFe2om2gboUz4g

   *We then construct the following JWE header:*



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     {"alg":"XC20PKW","enc":"XC20P","iv":"LuNNS5RAagkOQVewQOLRp9noXET
     _YsPX","tag":"VT2Z9a93JFe2om2gboUz4g"}

   *The next step is to prepare the content encryption:*

   AAD (Base64URL)

     eyJhbGciOiJYQzIwUEtXIiwiZW5jIjoiWEMyMFAiLCJpdiI6Ikx1Tk5TNVJBYWdr
     T1FWZXdRT0xScDlub1hFVF9Zc1BYIiwidGFnIjoiVlQyWjlhOTNKRmUyb20yZ2Jv
     VXo0ZyJ9

   Key (generated earlier):

                la2knCeFPAvUE2IVPm-RNrwj4UrHffLU6Y1tx3d5T1Q

   Nonce (Base64URL)

                     LHs6vru3ggyuAzgT2UJkWyqJuZSv0Gae

   *We then encrypt the payload with XChacha20-Poly1309 using the
   previous parameters, which results in the following output:*

   Ciphertext (Base64URL)

                             QgxRd4qQrkQNaEK3

   Tag (Base64URL)

                          aQDs_RkdWabvzmxYEnoShg

   *Lastly, we combine all the previous outputs to form the following
   JWE:*

     eyJhbGciOiJYQzIwUEtXIiwiZW5jIjoiWEMyMFAiLCJpdiI6Ikx1Tk5TNVJBYWdr
     T1FWZXdRT0xScDlub1hFVF9Zc1BYIiwidGFnIjoiVlQyWjlhOTNKRmUyb20yZ2Jv
     VXo0ZyJ9.K-kXEFjmSsjKzU91.LHs6vru3ggyuAzgT2UJkWyqJuZSv0Gae.QgxRd
     4qQrkQNaEK3.aQDs_RkdWabvzmxYEnoShg

Appendix B.  Example using ECDH-ES+XC20PKW

   *Considering the payload of "Hello World!"  (Base64URL):*

                             SGVsbG8gV29ybGQh

   *We begin by generating the XChacha20-Poly1309 content encryption key
   (Base64URL):*

                O2-TuP5Qz_ab6N61LhVS6asFdN_X5zF0YhJ6Df0vtoE



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   *We follow by encrypting the CEK using XChacha20-Poly1309 itself
   following a key agreement.  We generate a new key pair:*

   Private X (Base64URL)

                OtbkdOjp6SIgQ-TMXlqg48Ds8ycsSCxadJrjCurCcSM

   Public X (Base64URL)

                xxXXpDLvS0z-Zlx5J6dsVPPVonYufe9zTKfat0dEryM

   *Using the recipient public key, we generate a shared secret*

   Recipient PK (Base64URL)

                8llBJmFOkoFO8TYhFyDFm90Z8c6ytiD18wUgM5alCHY

   Shared Secret (Base64URL)

                llX-1dAQU6BiuTDUq4DgRy9Ob-1zoLp-1hvmKa8baGk

   *We can now derive a KEK:*

   APU (Base64URL)

     Q2tkNDNqSkZNb2FHeGVJZW9FUHgtNF9SYlNmLWd1T19MRHpvbDhrLWFnM2NELXhm
     dzdWX1IzM0lXVHRDZ0NqVmhmWTVQa29aT3AyTGwxZTR5ZWZ4d2c

   KEK (Base64URL)

                jPC4ybPvJ-FF4qz7hYiHDxr7XGQdQCMDjWaQ-y_MJfQ

   *We can now perform XChacha20-Poly1309 on the CEK using a new random
   nonce:*

   Nonce (Base64URL)

                     1Ef_Hs3NdFIujh9-uZEYLz4N_b1K1CJl

   Ciphertext (Base64URL)

                             mzHMc5XlqW-jkGP4

   Tag (Base64URL)

                          G8A4JnNmsG2wgvQh6Q5A8g

   *We then construct the following JWE header:*



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     {"alg":"ECDH-ES+XC20PKW","enc":"XC20P","iv":"1Ef_Hs3NdFIujh9-uZE
     YLz4N_b1K1CJl","tag":"G8A4JnNmsG2wgvQh6Q5A8g","apu":"Q2tkNDNqSkZ
     Nb2FHeGVJZW9FUHgtNF9SYlNmLWd1T19MRHpvbDhrLWFnM2NELXhmdzdWX1IzM0l
     XVHRDZ0NqVmhmWTVQa29aT3AyTGwxZTR5ZWZ4d2c","epk":{"typ":"OKP","cr
     v":"X25519","x":"xxXXpDLvS0z-Zlx5J6dsVPPVonYufe9zTKfat0dEryM"}}

   *The next step is to prepare the content encryption:*

   AAD (Base64URL)

     eyJhbGciOiJFQ0RILUVTK1hDMjBQS1ciLCJlbmMiOiJYQzIwUCIsIml2IjoiMUVm
     X0hzM05kRkl1amg5LXVaRVlMejROX2IxSzFDSmwiLCJ0YWciOiJHOEE0Sm5ObXNH
     MndndlFoNlE1QThnIiwiYXB1IjoiUTJ0a05ETnFTa1pOYjJGSGVHVkpaVzlGVUhn
     dE5GOVNZbE5tTFdkMVQxOU1SSHB2YkRockxXRm5NMk5FTFhobWR6ZFdYMUl6TTBs
     WFZIUkRaME5xVm1obVdUVlFhMjlhVDNBeVRHd3haVFI1WldaNGQyYyIsImVwayI6
     eyJ0eXAiOiJPS1AiLCJjcnYiOiJYMjU1MTkiLCJ4IjoieHhYWHBETHZTMHotWmx4
     NUo2ZHNWUFBWb25ZdWZlOXpUS2ZhdDBkRXJ5TSJ9fQ

   Key (generated earlier):

                O2-TuP5Qz_ab6N61LhVS6asFdN_X5zF0YhJ6Df0vtoE

   Nonce (Base64URL)

                     okZz0AJz-PfUL4OGjioPLsg6-siwyq2I

   *We then encrypt the payload with XChacha20-Poly1309 using the
   previous parameters, which results in the following output:*

   Ciphertext (Base64URL)

                             yxpuuXB7DcXBlyVE

   Tag (Base64URL)

                          IwvDEC8hxltfzidjmUKeMg

   *Lastly, we combine all the previous outputs to form the following
   JWE:*












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     eyJhbGciOiJFQ0RILUVTK1hDMjBQS1ciLCJlbmMiOiJYQzIwUCIsIml2IjoiMUVm
     X0hzM05kRkl1amg5LXVaRVlMejROX2IxSzFDSmwiLCJ0YWciOiJHOEE0Sm5ObXNH
     MndndlFoNlE1QThnIiwiYXB1IjoiUTJ0a05ETnFTa1pOYjJGSGVHVkpaVzlGVUhn
     dE5GOVNZbE5tTFdkMVQxOU1SSHB2YkRockxXRm5NMk5FTFhobWR6ZFdYMUl6TTBs
     WFZIUkRaME5xVm1obVdUVlFhMjlhVDNBeVRHd3haVFI1WldaNGQyYyIsImVwayI6
     eyJ0eXAiOiJPS1AiLCJjcnYiOiJYMjU1MTkiLCJ4IjoieHhYWHBETHZTMHotWmx4
     NUo2ZHNWUFBWb25ZdWZlOXpUS2ZhdDBkRXJ5TSJ9fQ.mzHMc5XlqW-jkGP4.okZz
     0AJz-PfUL4OGjioPLsg6-siwyq2I.yxpuuXB7DcXBlyVE.IwvDEC8hxltfzidjmU
     KeMg

Author's Address

   Guillaume Amringer
   Canada

   Email: g.amringer@gmail.com



































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