Use of EdDSA Signatures in the Cryptographic Message Syntax (CMS)

Document Type Active Internet-Draft (individual)
Author Russ Housley 
Last updated 2016-04-18
Replaced by RFC 8419, RFC 8419
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Internet-Draft                                                R. Housley
Intended status: Standards Track                          Vigil Security
Expires: 20 October 2016                                   18 April 2016

   Use of EdDSA Signatures in the Cryptographic Message Syntax (CMS)



   This document describes the conventions for using Edwards-curve
   Digital Signature Algorithm (EdDSA) in the Cryptographic Message
   Syntax (CMS).  The conventions for Ed25519, Ed25519ph, Ed448, and
   Ed448ph are described.

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1.  Introduction

   This document specifies the conventions for using the Edwards-curve
   Digital Signature Algorithm (EdDSA) [EDDSA] with the Cryptographic
   Message Syntax [CMS] signed-data content type.  The conventions for
   two recommended elliptic curves are specified, Ed25519 and Ed448.
   For each curve, two modes are defined, the PureEdDSA mode without
   pre-hashing (Ed25519 and Ed448), and the HashEdDSA mode with pre-
   hashing (Ed25519ph and Ed448ph).

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [STDWORDS].

1.2.  ASN.1

   CMS values are generated using ASN.1 [X680], which uses the Basic
   Encoding Rules (BER) and the Distinguished Encoding Rules (DER)

2.  EdDSA Signature Algorithm

   The Edwards-curve Digital Signature Algorithm (EdDSA) {EDDSA] is a
   variant of Schnorr's signature system with (possibly twisted) Edwards
   curves.  Ed25519 is intended to operate at around the 128-bit
   security level, and Ed448 at around the 224-bit security level.

   A message digest is computed over the data to be signed using EdDSA,
   and then a private key operation is performed to generate the
   signature value.  As described in Section 3.3 of [EDDSA], the
   signature value is the opaque value ENC(R) || ENC(S).  As described
   in Section 5.3 of [CMS], the signature value is ASN.1 encoded as an
   OCTET STRING and included in the signature field of SignerInfo.

2.1.  Certificate Identifiers

   The EdDSA signature algorithm is defined in [EDDSA], and the
   conventions for encoding the public key are defined in [PKIXEDDSA].

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

      id-EdDSAPublicKey OBJECT IDENTIFIER ::= { 1 3 101 100 }

   When the id-EdDSAPublicKey onject identifier is used, the
   AlgorithmIdentifier parameters field MUST contain EdDSAParameters to
   specify a particular set of EdDSA parameters:

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      EdDSAParameters ::= ENUMERATED {
        ed25519   (1),    -- PureEdDSA
        ed25519ph (2),    -- HashEdDSA
        ed448     (3),    -- PureEdDSA
        ed448ph   (4) }   -- HashEdDSA

2.2.  Signature Identifiers

   The algorithm identifier for EdDSA signatures is:

      id-EdDSASignature OBJECT IDENTIFIER ::= { 1 3 101 101 }

   When the id-EdDSASignature object identifier is used for a signature,
   the AlgorithmIdentifier parameters field MUST be absent.

3.  Signed-data Conventions

   digestAlgorithms SHOULD contain the one-way hash function used to
   compute the message digest on the eContent value.

   The same one-way hash function SHOULD be used for computing the
   message digest on both the eContent and the signedAttributes value if
   signedAttributes are present.

   signatureAlgorithm MUST contain id-EdDSASignature.  The algorithm
   parameters field MUST be absent.

   signature contains the single value resulting from the EdDSA signing

4.  Security Considerations

   Implementations must protect the EdDSA private key.  Compromise of
   the EdDSA private key may result in the ability to forge signatures.

   The generation of EdDSA private key relies on random numbers.  The
   use of inadequate pseudo-random number generators (PRNGs) to generate
   these values can result in little or no security.  An attacker may
   find it much easier to reproduce the PRNG environment that produced
   the keys, searching the resulting small set of possibilities, rather
   than brute force searching the whole key space.  The generation of
   quality random numbers is difficult.  RFC 4086 [RANDOM] offers
   important guidance in this area.

   Using the same private key for different algorithms has the potential
   of allowing an attacker to get extra information about the key.  It
   is strongly suggested that the same key not be used with more than
   one EdDSA set of parameters.

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   When computing signatures, the same hash function should be used for
   all operations.  This reduces the number of failure points in the
   signature process.

5.  Normative References

   [CMS]      Housley, R., "Cryptographic Message Syntax (CMS)", RFC
              5652, September 2009.

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

              Josefsson, S., "Using Curve25519 and Curve448 in PKIX",
              draft-ietf-curdle-pkix-eddsa-00, (work in progress),
              October 2015.

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

   [X680]     ITU-T, "Information technology -- Abstract Syntax Notation
              One (ASN.1): Specification of basic notation", ITU-T
              Recommendation X.680, 2002.

   [X690]     ITU-T, "Information technology -- ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)", ITU-T Recommendation X.690, 2002.

6.  Informative References

   [RANDOM]   Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", RFC 4086, June 2005.

Author Address

   Russ Housley
   918 Spring Knoll Drive
   Herndon, VA 20170

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