Use of EdDSA Signatures in the Cryptographic Message Syntax (CMS)
draft-ietf-curdle-cms-eddsa-signatures-08

Document Type Active Internet-Draft (curdle WG)
Last updated 2017-10-16 (latest revision 2017-10-12)
Replaces draft-housley-cms-eddsa-signatures
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Internet-Draft                                                R. Housley
Intended status: Standards Track                          Vigil Security
Expires: 11 April 2018                                   11 October 2017

   Use of EdDSA Signatures in the Cryptographic Message Syntax (CMS)
            <draft-ietf-curdle-cms-eddsa-signatures-08.txt>

Abstract

   This document specifies the conventions for using Edwards-curve
   Digital Signature Algorithm (EdDSA) for curve25519 and curve448 in
   the Cryptographic Message Syntax (CMS).  For each curve, EdDSA
   defines the PureEdDSA and HashEdDSA modes.  However, the HashEdDSA
   mode is not used with the CMS.  In addition, no context string is
   used with the CMS.

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Housley              Using EdDSA Signatures with CMS            [Page 1]
Internet-Draft                                              October 2017

1.  Introduction

   This document specifies the conventions for using the Edwards-curve
   Digital Signature Algorithm (EdDSA) [RFC8032] for curve25519
   [CURVE25519] and curve448 [CURVE448] with the Cryptographic Message
   Syntax (CMS) [RFC5652] signed-data content type.  For each curve,
   [RFC8032] defines the PureEdDSA and HashEdDSA modes; however, the
   HashEdDSA mode is not used with the CMS.  In addition, no context
   string is used with CMS.  EdDSA with curve25519 is referred to as
   Ed25519, and EdDSA with curve448 is referred to as Ed448.  The CMS
   conventions for PureEdDSA with Ed25519 and Ed448 are described in
   this document.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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)
   [X690].

2.  EdDSA Signature Algorithm

   The Edwards-curve Digital Signature Algorithm (EdDSA) [RFC8032] 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.

   One of the parameters of the EdDSA algorithm is the "prehash"
   function.  This may be the identity function, resulting in an
   algorithm called PureEdDSA, or a collision-resistant hash function,
   resulting in an algorithm called HashEdDSA.  In most situations the
   CMS SignedData includes signed attributes, including the message
   digest of the content.  Since HashEdDSA offers no benefit when signed
   attributes are present, only PureEdDSA is used with the CMS.

2.1.  Algorithm Identifiers

   Each algorithm is identified by an object identifier, and the
   algorithm identifier may contain parameters if needed.

Housley              Using EdDSA Signatures with CMS            [Page 2]
Internet-Draft                                              October 2017

   The ALGORITHM definition is repeated here for convenience:
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