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Network Working Group                                       S. Josefsson
Internet-Draft                                                    SJD AB
Intended status: Informational                              June 8, 2015
Expires: December 10, 2015


  Using EdDSA/Ed25519 in the Internet X.509 Public Key Infrastructure
                     draft-josefsson-pkix-eddsa-00

Abstract

   This document specify algorithm identifiers and ASN.1 encoding
   formats for EdDSA/Ed25519 digital signatures and subject public keys
   used in the Internet X.509 Public Key Infrastructure (PKIX) for
   Certificates and CRLs.

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 December 10, 2015.

Copyright Notice

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

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1.  Introduction

   In [Ed25519], an elliptic curve signature system EdDSA was
   introduced, and a recommended choice of curve Ed25519 is chosen.
   Ed25519 was designed with performance and security in mind.  EdDSA
   and Ed25519 is also described in [I-D.josefsson-eddsa-ed25519].

   This RFC defines ASN.1 object identifiers for EdDSA and Ed25519 for
   use in the Internet X.509 PKI [RFC5280].  This document serves a
   similar role as [RFC3279] does for RSA (and more), [RFC4055] for RSA-
   OAEP/PSS, and [RFC5758] for SHA2-based (EC)DSA.

2.  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].

3.  EdDSA ASN.1 Object Identifier Tree

   The root of the tree for the object identifiers defined in this
   specification is given by:

       id-EdDSA OBJECT IDENTIFIER ::= { 1.3.6.1.4.1.11591.4.12 }

4.  Subject Public Key Information Fields

   In the X.509 certificate, the subjectPublicKeyInfo field has the
   SubjectPublicKeyInfo type, which has the following ASN.1 syntax:

        SubjectPublicKeyInfo  ::=  SEQUENCE  {
          algorithm         AlgorithmIdentifier,
          subjectPublicKey  BIT STRING
        }

   The fields in SubjectPublicKeyInfo have the following meanings:

   o  algorithm is the algorithm identifier and parameters for the
      public key (see below).

   o  subjectPublicKey is the EdDSA public key.

   The AlgorithmIdentifier type, which is included for convenience, is
   defined as follows:







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         AlgorithmIdentifier  ::=  SEQUENCE  {
           algorithm   OBJECT IDENTIFIER,
           parameters  ANY DEFINED BY algorithm OPTIONAL
         }

   The fields in AlgorithmIdentifier have the following meanings:

   o  algorithm identifies the cryptographic algorithm with an object
      identifier.  This is the EdDSA OID defined below.

   o  parameters, which are optional, are the associated parameters for
      the algorithm identifier in the algorithm field.

5.  EdDSA Public Keys

   Certificates conforming to [RFC5280] may convey a public key for any
   public key algorithm.  The certificate indicates the algorithm
   through an algorithm identifier.  This algorithm identifier is an OID
   and optionally associated parameters.

   This section identify the OID and parameters for the EdDSA algorithm.
   Conforming CAs MUST use the identified OIDs when issuing certificates
   containing EdDSA public keys.  Conforming applications supporting
   EdDSA MUST, at a minimum, recognize the OID identified in this
   section.

   The id-EdDSAPublicKey OID is used for identifying EdDSA public keys.

          id-EdDSAPublicKey OBJECT IDENTIFIER ::= { id-EdDSA 1 }

   The id-EdDSAPublicKey OID is intended to be used in the algorithm
   field of a value of type AlgorithmIdentifier.  The parameters field
   MUST have ASN.1 type NULL for this algorithm identifier.

   [[TODO: We need to clarify the curve choice.  I see two options: 1)
   Let the OID defined here mean Ed25519 directly.  2) Let the OID
   defined here mean EdDSA, and specify a parameters structure (maybe
   reusing RFC 3279's EcpkParameters) and another NamedCurve OID to
   refer to Ed25519.  The second is only useful if EdDSA will ever be
   used with other curves.]]

   The EdDSA public key MUST be encoded using the ASN.1 type
   EdDSAPublicKey:

          EdDSAPublicKey ::= OCTET STRING -- LE edwards point






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   where the value is the little-endian encoded edwards point.  The DER
   encoded EdDSAPublicKey is the value of the BIT STRING
   subjectPublicKey.

6.  Key Usage Bits

   The intended application for the key MAY be indicated in the keyUsage
   certificate extension.

   If the keyUsage extension is present in an end-entity certificate
   that conveys an EdDSA public key with the id-EdDSAPublicKey object
   identifier, then the keyUsage extension MUST contain one or both of
   the following values:

          nonRepudiation; and
          digitalSignature.

   If the keyUsage extension is present in a certification authority
   certificate that conveys an EdDSA public key with the id-
   EdDSAPublicKey object identifier, then the keyUsage extension MUST
   contain one or more of the following values:

          nonRepudiation;
          digitalSignature;
          keyCertSign; and
          cRLSign.

7.  EdDSA Signatures

   Certificates and CRLs conforming to [RFC5280] may be signed with any
   public key signature algorithm.  The certificate or CRL indicates the
   algorithm through an algorithm identifier which appears in the
   signatureAlgorithm field within the Certificate or CertificateList.
   This algorithm identifier is an OID and has optionally associated
   parameters.  For illustration the Certificate structure is reproduced
   here:

      Certificate  ::=  SEQUENCE  {
           tbsCertificate       TBSCertificate,
           signatureAlgorithm   AlgorithmIdentifier,
           signatureValue       BIT STRING  }

   Also recall the definition of the AlgorithmIdentifier type:

         AlgorithmIdentifier  ::=  SEQUENCE  {
           algorithm   OBJECT IDENTIFIER,
           parameters  ANY DEFINED BY algorithm OPTIONAL
         }



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   This document identify an AlgorithmIdentifier OID for EdDSA
   signatures.  No parameters are defined.

   The data to be signed is prepared for EdDSA.  Then, a private key
   operation is performed to generate the signature value.  This
   signature value is then ASN.1 encoded as a BIT STRING and included in
   the Certificate or CertificateList in the signature field.

   The id-EdDSASignature OID is used for identifying EdDSA signatures.

          id-EdDSASignature OBJECT IDENTIFIER ::= { id-EdDSA 2 }

   The id-EdDSASignature OID is intended to be used in the algorithm
   field of a value of type AlgorithmIdentifier.  The parameters field
   MUST have ASN.1 type NULL for this algorithm identifier.

8.  Acknowledgements

   Text and/or inspiration were drawn from [RFC5280], [RFC3279],
   [RFC4055], [RFC5480], and [RFC5639].

   Thanks to Ilari Liusvaara for ideas and discussion.

9.  IANA Considerations

   None.

10.  Security Considerations

   The security considerations of [RFC5280] and
   [I-D.josefsson-eddsa-ed25519] apply accordingly.

11.  References

11.1.  Normative References

   [I-D.josefsson-eddsa-ed25519]
              Josefsson, S. and N. Moller, "EdDSA and Ed25519", draft-
              josefsson-eddsa-ed25519-02 (work in progress), February
              2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.



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11.2.  Informative References

   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, April 2002.

   [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
              Algorithms and Identifiers for RSA Cryptography for use in
              the Internet X.509 Public Key Infrastructure Certificate
              and Certificate Revocation List (CRL) Profile", RFC 4055,
              June 2005.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, March 2009.

   [RFC5639]  Lochter, M. and J. Merkle, "Elliptic Curve Cryptography
              (ECC) Brainpool Standard Curves and Curve Generation", RFC
              5639, March 2010.

   [RFC5758]  Dang, Q., Santesson, S., Moriarty, K., Brown, D., and T.
              Polk, "Internet X.509 Public Key Infrastructure:
              Additional Algorithms and Identifiers for DSA and ECDSA",
              RFC 5758, January 2010.

   [Ed25519]  Bernstein, J., Duif, , Lange, , Schwabe, , and Yang,
              "Ed25519: High-speed high-security signatures", WWW
              http://ed25519.cr.yp.to/ed25519-20110926.pdf, September
              2011.

Author's Address

   Simon Josefsson
   SJD AB

   Email: simon@josefsson.org














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