Internet DRAFT - draft-housley-cms-eddsa-signatures
draft-housley-cms-eddsa-signatures
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)
<draft-housley-cms-eddsa-signatures-00.txt>
Abstract
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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)
[X690].
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
operation.
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.
[PKIXEDDSA]
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
USA
housley@vigilsec.com
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