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Network Working Group                                    P. Hallam-Baker
Internet-Draft                                         Comodo Group Inc.
Intended status: Informational                            April 11, 2018
Expires: October 13, 2018


                           JSON Key Exchange
                 draft-hallambaker-json-key-exchange-03

Abstract

   The JSON Key Exchange

   This document is also available online at
   http://mathmesh.com/Documents/draft-hallambaker-json-key-
   exchange.html [1] .

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 October 13, 2018.

Copyright Notice

   Copyright (c) 2018 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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Defined Terms . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Related Specifications  . . . . . . . . . . . . . . . . .   4
     2.4.  Implementation Status . . . . . . . . . . . . . . . . . .   4
   3.  Key Exchange Protocol . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Roles . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Keys  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.5.  Derived Keys  . . . . . . . . . . . . . . . . . . . . . .   5
     3.6.  Initial Keying Request  . . . . . . . . . . . . . . . . .   6
       3.6.1.  Initial Request Message . . . . . . . . . . . . . . .   6
       3.6.2.  Initial Response Message  . . . . . . . . . . . . . .   6
     3.7.  Rekeying. . . . . . . . . . . . . . . . . . . . . . . . .   6
       3.7.1.  Rekeying Request Message  . . . . . . . . . . . . . .   7
       3.7.2.  Rekeying Response Message . . . . . . . . . . . . . .   7
     3.8.  Initial Key Exchange Example  . . . . . . . . . . . . . .   7
     3.9.  Rekey Example . . . . . . . . . . . . . . . . . . . . . .  10
   4.  Key Exchange Service  . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Shared classes  . . . . . . . . . . . . . . . . . . . . .  10
       4.1.1.  Structure: Algorithms . . . . . . . . . . . . . . . .  10
     4.2.  Utility Transactions  . . . . . . . . . . . . . . . . . .  10
     4.3.  Transaction: Exchange . . . . . . . . . . . . . . . . . .  10
       4.3.1.  Message: ExchangeRequest  . . . . . . . . . . . . . .  10
       4.3.2.  Message: ExchangeResponse . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
     7.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   This document describes a lightweight key agreement mechanism using
   between 2 and four Diffe-Hellman or Elliptic Curve Diffie-Hallman
   keys.  The mechanism may be used establish a shared session key with
   authentication of any or none of the initiator and the responder.

   The approach described is similar to that adopted in the X3DH Key
   agreement [X3DH] used in Signal.





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   The objective of the key exchange is limited to establishing a shared
   secret between two mutually authenticated parties that cannot be
   derived by any other parties and cannot be reconstructed by either of
   the parties after the ephemeral contributions have been deleted.

   The key exchange is intended for use as one component in a multi-
   layer security approach in which comprehensive security is provided
   through use of encryption and authentication at multiple layers in
   the protocol stack.

   [[This figure is not viewable in this format.  The figure is
   available at http://mathmesh.com/Documents/draft-hallambaker-json-
   key-exchange.html [2].]]


   Multi-layer security

   Specifically, this key exchange is intended for use at the
   presentation layer (e.g. authenticate and encrypt HTTP message
   bodies) to establish keys for authentication and optional encryption
   of messages in Web Service transactions.

   Data Layer  Encryption of cryptographic keys, protocol configuration
      profiles.

   Presentation Layer  Authentication of parties to a Web Service
      transaction.

   Transport Layer  Protect metadata against interception at single
      point on the message path (link or node)

   Link Layer  Protect messages against traffic analysis by means of
      interception at multiple points on the message path

2.  Definitions

   This section presents the related specifications and standard, the
   terms that are used as terms of art within the documents and the
   terms used as requirements language.

2.1.  Requirements Language

   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].






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2.2.  Defined Terms

   No terms of art are defined.

2.3.  Related Specifications

   JSON Key Exchange is used extensively in the Mathematical Mesh and
   related protocols [draft-hallambaker-mesh-architecture] .

2.4.  Implementation Status

   The implementation status of the reference code base is described in
   the companion document [draft-hallambaker-mesh-developer] .

3.  Key Exchange Protocol

3.1.  Parameters

   The following parameters are defined

   Algorithm  The key exchange protocol.  Diffie Hellman in discrete
      log, EdECDH25519 or EdECDH448.[RFC8032]

   Key Derivation Function  The key derivation function.  This is always
      HKDF [RFC5869]

   Key Wrap Function  The Key Wrap function.  This is always RFC3394
      [RFC3394]

   It should be noted that the algorithm described makes use of the
   Edwards form of the curve and not the Montgomery form described in
   [RFC7748] . While these curves are isomorphic, implementations of the
   Montgomery ladder do not lend themselves easily to the approach
   shown.

3.2.  Notation

   The notation adopted in [X3DH] is applied with minor modifications.

   X ||Y  The concatenation of the byte sequence X followed by the byte
      sequence Y.

   KE (PK1, PK2)  The result of performing the key exchange (Diffie-
      Hellman or Elliptic Curve Diffie Hellman) with the public
      parameters of PK1 and the private parameters of PK2.

   PK1+PK2  The public, private key pair formed by combining the public,
      private parameters of PK1 and PK2.



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   Expand (PRK, info, L)  The KDF expansion function that derives a key
      of length L bits from the Pre Random Key PRK using the string info
      as the salt.

   Extract (IKM, salt)  The KDF extraction function that derives a Pre-
      Random Key from the Initial Keying Material IKM and the salt value
      salt.  If the salt value is specified as 0, the default salt of a
      string of zero bits the same length as the Pre-Random Key to be
      extracted is used.

3.3.  Roles

   Client  The party that initiates the key exchange

   Service  The party that responds to the key exchange

3.4.  Keys

   IKC  The identification key of the client.  The encoding of this key
      MAY include one or more credentials such as a Mesh personal
      profile or an X.509 certificate binding the key to an identity.

   IKS   The identification key of the service.  The encoding of
      this key MAY include one or more credentials such as a Mesh
      personal profile or an X.509 certificate binding the key to an
      identity.

   EKC   The ephemeral key of the client.

   EKS   The ephemeral key of the service.

3.5.  Derived Keys

   The key derivation function is used to derive separate keys for
   different purposes as shown below.  The value L is the number of bits
   requires to key the algorithm specified.  The salt value used to
   derive the PRK from the IKM is either the default salt value (all
   zeros) or the previous Rekey value as described below.

   AK (PRK)  Authentication Key = Expand (PRK, "authentication", L)

   EK (PRK)  Encryption Key = Expand (PRK, "encryption", L)

   RA (PRK)  Rekey Key = Expand (PRK, "rekey", L)

   W (PRK)  Witness value= Expand (PRK, "witness", L)





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3.6.  Initial Keying Request

   A key exchange request is either an initial key exchange request or a
   rekeying request.  An initial key exchange request MAY be issued at
   any time but a rekeying request cannot be sent until at least one
   initial keying request has been completed.

   Rekey messages are authenticated under a Rekey shared secret
   established in a previous session.  This may be the immediately
   preceding session or any prior session whose rekey token has not
   expired.

3.6.1.  Initial Request Message

   The client sends their identity and ephemeral key to the service. {
   IKC, EKC }

   If the request message is an initial keying request, a credential
   associated with the identity key MAY be provided.  The request MAY be
   authenticated by means of a digital signature.

3.6.2.  Initial Response Message

   The service calculates the IKM value as follows:

   IKM = KE (IKC + EKC, IKS + EKS)

   PRK = Extract (IKM, 0)

   The service returns the values { IKS, EKS, W(IKM) } in a message
   authenticated under AK(IKM)

3.7.  Rekeying.

   Unless the key agreement is performed to a device of restricted
   capability, rekeying imposes minimal load on client or server and can
   be performed often, particularly if the Ed25519 curve is used for
   rekeying.

   The state required for rekeying is separate from the keys used to
   encrypt and/or authenticate messages.  This allows an application to
   store the rekeying key between communication sessions without risk of
   compromising the confidentiality or integrity of messages.

   The use of the chaining salt ensures that rekeying cannot compromise
   the security of an already established key, even if a weaker key
   exchange algorithm is used.  Thus a client MAY use an Ed488 key to




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   perform an initial key exchange and then preform rekey operations
   using a

3.7.1.  Rekeying Request Message

   The client sends a new ephemeral key to the service. { CEK }

   The request message MUST be authenticated under the rekeying key of
   the shared secret of any unexpired session previously agreed.  This
   allows the credentials of the parties to be omitted while providing
   the advantage of establishing a fresh forward secrecy session.

3.7.2.  Rekeying Response Message

   The service calculates the IKM value as follows:

   IKM = KE (EKC, EKS)

   The service returns the values { EKS, W(IKM) } in a message
   authenticated under AK(IKM)

   PRK = Extract (IKM, RA')

   Where RA' is the previous rekeying key output.

3.8.  Initial Key Exchange Example

   Alice requests access to a service using her account identifier
   alice@example.com.  She has already registered her Mesh personal
   profile with the service where it is bound to her account identifier
   as the corresponding credential.

   The Key exchange request is:


















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   POST /.well-known/jwcexchange/HTTP/1.1
   Host: example.com
   Content-Length: 1068

   {
     "ExchangeRequest": {
       "ClientCredential": {
         "PublicKeyDH": {
           "kid": "MB5OU-335BC-AUKOZ-E62ZE-4ME2J-IYUVJ",
           "Domain": "
   YE6bnq1MlX5ojaJto6PLP_PEwA",
           "Public": "
   5PxAR4YJvsf7XS1m25OnhkSh_F5yopwHCClxQZO4I2w5uc-twDYhRhFPazUBBKkT
   G7ruS1qFJC-vuzcI6UL9Ee0QeJ9plnWoJA5CsoTFg_dHQVKEkdW5D227NT5OnvCe
   AH1yinKSoIcRh4CXSG3MMC9oBOIj7YF4oWSgJ-T4ruMLXONac-o6T_2h-00dD9OP
   Mpkj8_OdX3TdNwKnkSNJRrGj5F8UunJU9C85Tr1eh-U7wzW753RaqwN3R-B3LVjl
   t4d1qiKbqGEzSjknSrjtUIReuAYtCI0fqOTap-6XcvdB_SHs4vPZ8oErIU0aTB65
   VTtje5fm16tp-3o8P7x6WQ"}},
       "ClientNonce": {
         "PublicKeyDH": {
           "kid": "MB6Z6-GUF3J-RQRD3-IHIPS-UNOCI-HZDDR",
           "Domain": "
   YE6bnq1MlX5ojaJto6PLP_PEwA",
           "Public": "
   rVQmfx5-bSS6pTLwARcg_SyCBlNjZzWJ0yu9F7SE_2FuOJneQSqXOg1Gefz5UB2T
   dD3W8wyKHJHAPyvX05vhQcicGNKLB9MO5x4Pzn2Klwm0-W4jJNZ1qHjuy_l81six
   VqdGlRT44q9LTG326BJMmZMv_bij_lz3qTa8vOb9WTXfk458OV0ELphXmGSghi5t
   x_rrS9z9gpKR5a22qTraHpdQJvIpXO0HPGddn_sQ3K2DWCtfVTi7aiwr7kwsO3p6
   -NIHuAG4zRo86NE0UM_e6B4b7zX5cLt2n1_rqVNzwJOER1pRxgiFRtdJ43HyBVzv
   uW1BMrZzT0JCR9g5kGG_OA"}}}}

                                 Figure 1

   The Keyu Exchange response is

















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   HTTP/1.1 200 OK
   Date: Wed 11 Apr 2018 09:01:08
   Content-Length: 1360

   {
     "ExchangeResponse": {
       "Status": 201,
       "StatusDescription": "Operation completed successfully",
       "Ticket": "
   T3BhcXVlIHZhbHVlIG91dHNpZGUgc2NvcGUgb2Ygc3BlY2lmaWNhdGlvbg",
       "Witness": "
   tKE46P84C0qjGur7cbZNLxhfrU7NSEj98AKEIVh_zzg",
       "ServerCredential": {
         "PublicKeyDH": {
           "kid": "MDD5A-RFNE7-JNUOS-23LTY-O4NIJ-PAYKM",
           "Domain": "
   YE6bnq1MlX5ojaJto6PLP_PEwA",
           "Public": "
   W-SCGVPSf1zgtgj_hwlLLt_CQnYttpxn4Ze4r18B5UO-a8G1XxeQEUjjUUvRqDMX
   6KIWbrctjKOx2pIxAbMM3k9EzIk1lyvdhaXnSs-bBEHJpuqWzaz46JEt_49Nwppb
   _Qr0j4gFvqrr0Fr7uXIuoihF8byL7b4M69dvRT9wE1KQSw0hTdcnmWgN0x0IcWcY
   v3DTqGImtMibFkbgozj7csH-4UsMYDfqQx-DgGXLd0OkvN5CFqS030GRD9iDT9R4
   98TQgLK8YD6J08_i2ADAGiP_GwHvDHZHkq0jFkgris5JJvEbfXgS7h8yYEnzgUPL
   7xKt1vGcYs5ZQzHu8X6RGg"}},
       "ServerNonce": {
         "PublicKeyDH": {
           "kid": "MBD52-J4WFR-XKDUI-5BGL7-VHCQK-ZEHI7",
           "Domain": "
   YE6bnq1MlX5ojaJto6PLP_PEwA",
           "Public": "
   FkxMhJ64ZzdWI9QoBAeFEnB-9BupOu-B0FLmGMB9kkusumORQI-qiYQiGkEH93hH
   qSelOLGuM83VzC-SS3UQKmlDVb1rbRSCqZXbkLCnc8KHeiBp0r8rmVIH8XicYLhP
   _k9N5EjGmfcowGzOxZkO1d7g4sXEIv_Djr5hFf57F41zAvB34-ny2ZsD2jMyG4r5
   26bMr69ceLEwfqXx5_rDc3CljfC1cAdBMsZSslFokurzq9X0nF2maPeYRpN3Ytbn
   opzWmSyQZkoFg8Is9vnk6Dzy0mRHALpY0L6cMEEyYwNEhV7uGLMZsRtRLVDHvkAN
   q2vUlh-CxthTdIWYFLjw4wA"}},
       "Encryption": ["A256CBC-HS512"],
       "Authentication": ["HS512"]}}

                                 Figure 2

   Note that the example has the witness value but does not authenticate
   the signed result at present.  Perhaps it would be better to create
   the witness value from the ticket data which eliminates the need for
   authenticating the response??






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3.9.  Rekey Example

   (TBS)

4.  Key Exchange Service

   Supports key exchange to establish a shared secret and bound ticket
   between a client and a service

   HTTP Well Known Service Prefix: /.well-known/jwcexchange

   Every Recrypt Service transaction consists of exactly one request
   followed by exactly one response.

4.1.  Shared classes

4.1.1.  Structure: Algorithms

   Describes an algorithm suite.  Each suite consists of sets of
   authentication and encryption algorithms which are mutually
   compatible. i.e. the counterparty MAY select any one of the
   encryption algorithms and use it with any one of the authentication
   algorithms.

   Encryption: String [0..Many]  Algorithm identifiers of encryption and
      authenticated encryption algorithms offered

   Authentication: String [0..Many]  Authentication algorithm offer

4.2.  Utility Transactions

4.3.  Transaction: Exchange

   Request: ExchangeRequest

   Request: ExchangeRequest

   Response: ExchangeResponse

   Perform Key Exchange to establish shared key bound to a ticket.

4.3.1.  Message: ExchangeRequest

   Initiate the key exchange request.

   Offer: Algorithms [0..Many]  Set of message authentication and
      encryption algorithms offered by the client




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4.3.2.  Message: ExchangeResponse

   Returns the server parameters.

   Ticket: Binary (Optional)  Opaque session identifier.

   Witness: Binary (Optional)  Opaque witness value used to prove
      binding to the ticket.

   Encryption: String [0..Many]  Algorithm identifiers of encryption or
      authenticated encryption algorithm chosen

   Authentication: String [0..Many]  Algorithm identifiers of
      authentication algorithm chosen

5.  Security Considerations

6.  IANA Considerations

   The following registrations are required:

   HTTP Content Coding Registry  jose-jwb

   Well-Known URIs  /.well-known/srv/

      [Or change registry to FCFS]



7.  References

7.1.  Normative References

   [draft-hallambaker-mesh-architecture]
              Hallam-Baker, P., "Mathematical Mesh: Architecture",
              draft-hallambaker-mesh-architecture-04 (work in progress),
              September 2017.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
              September 2002.

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869,
              DOI 10.17487/RFC5869, May 2010.






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   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017.

7.2.  Informative References

   [draft-hallambaker-mesh-developer]
              Hallam-Baker, P., "Mathematical Mesh: Reference
              Implementation", draft-hallambaker-mesh-developer-06 (work
              in progress), April 2018.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016.

   [X3DH]     Marlinspike, M. and T. Perrin, "The X3DH Key Agreement
              Protocol", November 2011.

7.3.  URIs

   [1] http://mathmesh.com/Documents/draft-hallambaker-json-key-
       exchange.html

   [2] http://mathmesh.com/Documents/draft-hallambaker-json-key-
       exchange.html

Author's Address

   Phillip Hallam-Baker
   Comodo Group Inc.

   Email: philliph@comodo.com



















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