Re: [jose] CFRG ECC in JOSE - thumbprint

[Ilari Liusvaara <[e-mail]>]

On Wed, Nov 18, 2015 at 12:27:12AM +0000, Mike Jones wrote:
> I would strongly argue for using "crv" and "x" to characterize these
> algorithms.  Developers will be unpleasantly surprised if we don't
> and more than likely unnecessarily confused as well.

Well, I changed the text to use "crv" and "x" instead of "kag" and "p"
(and also changed "key algorithm group" to "key subtype", now from
EC registry, instead of algorithm registry).

As to confusion potential, I would say this is more confusing as it
uses the same parameter name for two quite different uses. 

> I'm on the fence about whether to use "kty":"EC" or a new key type
> value, such as "EC1" (Elliptic Curve with one coordinate).  I'll
> note that "EC" is already designed to allow curves whose
> representations use "x" but not "y", so there's strictly speaking no
> need for a new key type.  But I understand the argument that since
> "x" isn't represented in SEC1 format for these curves, that a
> different "kty" value may be appropriate.

Well, I kept the "OKP" name as I think it better describes what these
things are about than "EC1".

As for "EC", there is no guarantee these work for various ECC
algorithms one would expect to work for every curve (e.g. X25519 won't
work for signing, Ed25519 won't work for anything that presently
exists).

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Network Working Group                                       I. Liusvaara
Internet-Draft                                               Independent
Intended status: Standards Track                       November 18, 2015
Expires: May 21, 2016


                   CFRG curves and signatures in JOSE
                    draft-liusvaara-jose-cfrg-curves

Abstract

   This document defines how to use curves and algorithms from IRTF CFRG
   elliptic curves work (Diffie-Hellman and signatures) in 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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 21, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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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.  Requirements Terminology  . . . . . . . . . . . . . . . .   2
     1.2.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Key type 'OKP'  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Algorithms  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Signatures  . . . . . . . . . . . . . . . . . . . . . . .   3
       3.1.1.  Algorithms  . . . . . . . . . . . . . . . . . . . . .   3
       3.1.2.  Signing . . . . . . . . . . . . . . . . . . . . . . .   4
       3.1.3.  Verification  . . . . . . . . . . . . . . . . . . . .   4
     3.2.  ECDH-ES . . . . . . . . . . . . . . . . . . . . . . . . .   4
       3.2.1.  Performing the ECDH operation . . . . . . . . . . . .   4
   4.  Security considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   8
     A.1.  Ed25519 private key . . . . . . . . . . . . . . . . . . .   8
     A.2.  Ed25519 public key  . . . . . . . . . . . . . . . . . . .   9
     A.3.  JWK thumbprint canonicalization . . . . . . . . . . . . .   9
     A.4.  Ed25519 Signing . . . . . . . . . . . . . . . . . . . . .   9
     A.5.  Ed25519 Validation  . . . . . . . . . . . . . . . . . . .  10
     A.6.  ECDH-ES with X25519 . . . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Internet Research Task Force (IRTF) Crypto Forum Research Group
   (CFRG) selected new elliptic curves and signature algorithms for
   asymmetric key cryptography.  This document defines how those curves
   and algorithms are to be used in JOSE in interoperable manner.

   This extends [RFC7517] and [RFC7518]

1.1.  Requirements Terminology

   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].

1.2.  Notation

   All inputs to and outputs from the the ECDH and signature functions
   are defined to be octet strings, with the exception of output of
   verfication function, which is a boolean.



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2.  Key type 'OKP'

   A new key type (kty) value "OKP" (Octet Key Pair) is defined for
   public key algorithms that use octet strings as private and public
   keys.  It has the following parameters:

   o  The parameter "kty" MUST be "OKP".

   o  The parameter "crv" MUST be present, and contain the subtype of
      the key (from "JSON Web Elliptic curve" registry).

   o  The parameter "x" MUST be present, and contain the public key
      encoded using base64url [RFC4648] encoding.

   o  The parameter "d" MUST be present for private keys, and contain
      the private key encoded using base64url encoding.  This parameter
      MUST NOT be present for public keys.

   Note: Do not assume that there is an underlying elliptic curve,
   despite the existence of the "crv" and "x" parameters.

   When calculating thumbprints [RFC7638], the three public key fields
   are included in the hash.  That is, in lexographic order: "crv",
   "kty" and "x".

3.  Algorithms

3.1.  Signatures

3.1.1.  Algorithms

   The following signature algorithms are defined here (to be applied as
   values of "alg" parameter).  All these have keys with subtype of the
   same name:

     alg value:  subtype:     The algorithm:
     Ed25519     Ed25519      Ed25519
     Ed25519ph   Ed25519ph    Ed25519ph
     Ed448       Ed448        Ed448
     Ed448ph     Ed448ph      Ed448ph

   The key type for these keys is "OKP" and key subtype for these
   algorithms MUST be the same as the algorithm name.

   The keys of these subtypes MUST NOT be used for ECDH-ES.






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3.1.2.  Signing

   Signing for these is preformed by applying the signing algorithm
   defined in [I-D.irtf-cfrg-eddsa] to the private key (as private key),
   public key (as public key) and the JWS Signing Input (as message).
   The resulting signature is the JWS Signature value.  All inputs and
   outputs are octet strings.

3.1.3.  Verification

   Verification is performed by applying the verification algorithm
   defined in [I-D.irtf-cfrg-eddsa] to the public key (as public key),
   the JWS Signing Input (as message) and the JWS Signature value (as
   signature).  All inputs are octet strings.  If the algorithm accepts,
   the signature is valid, otherwise it is invalid.

3.2.  ECDH-ES

   The following key subtypes defined here for purpose of ECDH-ES:

      subtype:          ECDH Function:
      X25519            X25519
      X448              X448

   The key type used with these keys is "OKP".  These subtypes MUST NOT
   be used for signing.

3.2.1.  Performing the ECDH operation

   The "x" parameter of "epk" field is set as follows:

   Apply the appropriate ECDH function to the ephemeral private key (as
   scalar input) and the standard basepoint (as u-coordinate input).
   The output is the value for "x" parameter of "epk" field.  All inputs
   and outputs are octet strings.

   The Z value (raw key agreement output) for key agreement is
   determined as follows:

   Apply the appropriate ECDH function to the ephemeral private key (as
   scalar input) and receiver public key (as u-coordinate input).  The
   output is the Z value.  All inputs and outputs are octet strings.

4.  Security considerations

   Security considerations from [I-D.irtf-cfrg-curves] and
   [I-D.irtf-cfrg-eddsa] apply here.




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   Some algorithms interact in bad ways (e.g.  "Ed25519" and
   "Ed25519ph").  For this reason, those algorithms have different
   subtypes, so keys for each are not mixed up.

   Do not separate key material from information what key algorithm
   group it is for.  When using keys, check that the algorithm is
   compatible with the key algorithm group for the key.  To do otherwise
   opens system up to attacks via mixing up algorithms.  It is
   practicularly dangerous to mix up signature and MAC algorithms.

   Do not assume that signature also binds the key used for signing, it
   does not (there are also other widespread signature algorithms where
   this binding fails, as such binding is not part of the definition of
   secure signature primitive).  As an example of such failure, the
   Ed25519ph signature of X under key (Ed25519ph,Y) is identical to
   Ed25519 signature of SHA512(X) under key (Ed25519,Y).  And often it
   takes only setting a few bits of message (easy to do by brute force)
   to make the message valid enough to be processed in some very
   surprising way.

   If key generation or batch signature verification is performed, a
   well-seed cryptographical random number generator is REQUIRED.
   Signing and non-batch signature verification are deterministic
   operations and do not need random numbers of any kind.

5.  Acknowledgements

   Mike Jones for comments on initial pre-draft.

6.  IANA considerations

   The following is added to JSON Web Key Types Registry:

   o  "kty" Parameter Value: "OKP"
   o  Key Type Description: Octet string key pairs
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [RFC-THIS]


   The following is added to JSON Web Key Parameters Registry:

   o  Parameter Name: "crv"
   o  Parameter Description: The algorithm group of keypair
   o  Parameter Information Class: Public
   o  Used with "kty" Value(s): "OKP"
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [RFC-THIS]



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   o  Parameter Name: "d"
   o  Parameter Description: The private key
   o  Parameter Information Class: Private
   o  Used with "kty" Value(s): "OKP"
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [RFC-THIS]

   o  Parameter Name: "x"
   o  Parameter Description: The public key
   o  Parameter Information Class: Public
   o  Used with "kty" Value(s): "OKP"
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [RFC-THIS]


   The following is added to JSON Web Signature and Encryption
   Algorithms Registry:

   o  Algorithm Name: "Ed25519"
   o  Algorithm Description: Ed25519 signature algorithm
   o  Algorithm Usage Location(s): "alg"
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]
   o  Algorithm Analysis Documents(s): [I-D.irtf-cfrg-eddsa]

   o  Algorithm Name: "Ed25519ph"
   o  Algorithm Description: Ed25519 signature algorithm with prehash
   o  Algorithm Usage Location(s): "alg"
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]
   o  Algorithm Analysis Documents(s): [I-D.irtf-cfrg-eddsa]

   o  Algorithm Name: "Ed448"
   o  Algorithm Description: Ed448 signature algorithm
   o  Algorithm Usage Location(s): "alg"
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]
   o  Algorithm Analysis Documents(s): [I-D.irtf-cfrg-eddsa]

   o  Algorithm Name: "Ed448ph"
   o  Algorithm Description: Ed448 signature algorithm with prehash
   o  Algorithm Usage Location(s): "alg"
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]



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   o  Algorithm Analysis Documents(s): [I-D.irtf-cfrg-eddsa]


   The following is added to JSON Web Key Elliptic Curve Registry:

   o  Curve Name: "Ed25519"
   o  Curve Description: Ed25519 signature algorithm keypairs
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]

   o  Curve Name: "Ed25519ph"
   o  Curve Description: Ed25519 signature algorithm with prehash
      keypairs
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]

   o  Curve Name: "Ed448"
   o  Curve Description: Ed448 signature algorithm keypairs
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]

   o  Curve Name: "Ed448ph"
   o  Curve Description: Ed448 signature algorithm with prehash keypairs
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1 of [RFC-THIS]

   o  Curve name: "X25519"
   o  Curve Description: X25519 function keypairs
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.2 of [RFC-THIS]
   o  Analysis Documents(s): [I-D.irtf-cfrg-curves]

   o  Curve Name: "X448"
   o  Curve Description: X448 function keypairs
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.2 of [RFC-THIS]
   o  Analysis Documents(s): [I-D.irtf-cfrg-curves]








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7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <http://www.rfc-editor.org/info/rfc4648>.

   [I-D.irtf-cfrg-curves]
              Langley, A. and M. Hamburg, "Elliptic Curves for
              Security", draft-irtf-cfrg-curves-09 (work in progress),
              September 2015.

   [I-D.irtf-cfrg-eddsa]
              Josefsson, S. and I. Liusvaara, "Edwards-curve Digital
              Signature Algorithm (EdDSA)", draft-irtf-cfrg-eddsa-00
              (work in progress), October 2015.

7.2.  Informative References

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

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

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

Appendix A.  Examples

   To the extent possible, the examples use material lifted from test
   vectors of [I-D.irtf-cfrg-curves] and [I-D.irtf-cfrg-eddsa]

A.1.  Ed25519 private key

   {"kty":"OKP","crv":"Ed25519",
   "d":"nWGxne_9WmC6hEr0kuwsxERJxWl7MmkZcDusAxyuf2A"
   "x":"11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwIaaPcHURo"}




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   The hexadecimal dump of private key is:

   9d 61 b1 9d ef fd 5a 60 ba 84 4a f4 92 ec 2c c4
   44 49 c5 69 7b 32 69 19 70 3b ac 03 1c ae 7f 60

   And of the public key:

   d7 5a 98 01 82 b1 0a b7 d5 4b fe d3 c9 64 07 3a
   0e e1 72 f3 da a6 23 25 af 02 1a 68 f7 07 51 1a

A.2.  Ed25519 public key

   This is the public parts of the previous private key (just omits
   "d"):

   {"kty":"OKP","crv":"Ed25519",
   "x":"11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwIaaPcHURo"}

A.3.  JWK thumbprint canonicalization

   The JWK thumbprint canonicalization of the two above examples is
   (linebreak inserted for formatting reasons)

   {"crv":"Ed25519","kty":"OKP","x":"11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwI
   aaPcHURo"}

   Which has the SHA-256 hash of:
   90facafea9b1556698540f70c0117a22ea37bd5cf3ed3c47093c1707282b4b89

A.4.  Ed25519 Signing

   The JWS protected header is:

   {"alg":"Ed25519"}

   This has base64url encoding of:

   eyJhbGciOiJFZDI1NTE5In0

   The payload is (text):

   Example of Ed25519 signing

   This has base64url encoding of:

   RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc





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   The JWS signing input is (concatenation of base64url encoding of the
   (protected) header, a dot and base64url encoding of the payload) is:

   eyJhbGciOiJFZDI1NTE5In0.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc

   Applying Ed25519 signing algorithm to the private key, public key and
   the JWS signing input yields signature (hex):

   53 18 48 60 b1 c6 83 7f 4d 54 22 e9 40 05 43 fd
   47 1f 3a 69 c6 48 2c cb 15 9a 17 62 42 e2 21 b1
   5c 72 63 9b fe a3 9b b2 08 f3 2c ab 1f 27 0f b8
   36 57 1c 52 0b d8 ac 41 eb 45 b3 55 d0 77 19 01

   Converting this to base64url yields:

   UxhIYLHGg39NVCLpQAVD_UcfOmnGSCzLFZoXYkLiIbFccmOb_qObsgjzLKsfJw-4NlccU
   gvYrEHrRbNV0HcZAQ

   So the compact serialization of JWS is (concatenation of signing
   input, a dot and base64url encoding of the signature:

   eyJhbGciOiJFZDI1NTE5In0.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc.UxhIYLHGg
   39NVCLpQAVD_UcfOmnGSCzLFZoXYkLiIbFccmOb_qObsgjzLKsfJw-4NlccUgvYrEHrRb
   NV0HcZAQ

A.5.  Ed25519 Validation

   The JWS from above example is:

   eyJhbGciOiJFZDI1NTE5In0.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc.UxhIYLHGg
   39NVCLpQAVD_UcfOmnGSCzLFZoXYkLiIbFccmOb_qObsgjzLKsfJw-4NlccUgvYrEHrRb
   NV0HcZAQ

   This has 2 dots in it, so it might be valid JWS.  Base64url decoding
   the protected header yields:

   {"alg":"Ed25519"}

   So this is Ed25519 signature.  Now the key has: "kty":"OKP" and
   "crv":"Ed25519", so the key is valid for the algorithm (if it had
   other values, the validation would have failed).

   The signing input is the part before second dot:

   eyJhbGciOiJFZDI1NTE5In0.RXhhbXBsZSBvZiBFZDI1NTE5IHNpZ25pbmc






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   Applying Ed25519 verification algorithm to the public key, JWS
   signing input and the signature yields true.  So the signature is
   valid.  The message is base64 decoding of the part between the dots:

   Example of Ed25519 signing

A.6.  ECDH-ES with X25519

   The public key to encrypt to is:

   {"kty":"OKP","crv":"X25519","kid":"Bob"
   "x":"3p7bfXt9wbTTW2HC7OQ1Nz-DQ8hbeGdNrfx-FG-IK08"}

   The public key from target key is (hex):

   de 9e db 7d 7b 7d c1 b4 d3 5b 61 c2 ec e4 35 37
   3f 83 43 c8 5b 78 67 4d ad fc 7e 14 6f 88 2b 4f

   The ephemeral secret happens to be (hex):

   77 07 6d 0a 73 18 a5 7d 3c 16 c1 72 51 b2 66 45
   df 4c 2f 87 eb c0 99 2a b1 77 fb a5 1d b9 2c 2a

   So the ephemeral public key is X25519(ephkey,G) (hex):

   85 20 f0 09 89 30 a7 54 74 8b 7d dc b4 3e f7 5a
   0d bf 3a 0d 26 38 1a f4 eb a4 a9 8e aa 9b 4e 6a

   This is packed into ephemeral public key value:

   {"kty":"OKP","crv":"X25519",
   "x":"hSDwCYkwp1R0i33ctD73Wg2_Og0mOBr066SpjqqbTmo"}

   So the protected header could for example be:

   {"alg":"ECDH-ES+A128KW","epk":{"kty":"OKP","crv":"X25519",
   "x":"hSDwCYkwp1R0i33ctD73Wg2_Og0mOBr066SpjqqbTmo"},
   "enc":"A128GCM","kid":"Bob"}

   And sender computes as the DH Z value as X25519(ephkey,recv_pub)
   (hex):

   4a 5d 9d 5b a4 ce 2d e1 72 8e 3b f4 80 35 0f 25
   e0 7e 21 c9 47 d1 9e 33 76 f0 9b 3c 1e 16 17 42

   The receiver computes as the DH Z value as X25519(seckey,ephkey_pub)
   (hex):




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   4a 5d 9d 5b a4 ce 2d e1 72 8e 3b f4 80 35 0f 25
   e0 7e 21 c9 47 d1 9e 33 76 f0 9b 3c 1e 16 17 42

   Which is the same as sender's value (the both sides run this through
   KDF before using as AES128-KW key).

Author's Address

   Ilari Liusvaara
   Independent

   Email: [e-mail]







































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-Ilari