Network Working Group S. Josefsson
Internet-Draft SJD AB
Intended status: Standards Track May 20, 2015
Expires: November 21, 2015
EdDSA and Ed25519 for Transport Layer Security (TLS)
draft-josefsson-tls-eddsa-00
Abstract
This document introduce the public-key signature algorithm EdDSA for
use in Transport Layer Security (TLS). With the previous NamedCurve
and ECPointFormat assignments for the Curve25519 ECDHE key exchange
mechanism, this enables use of Ed25519 in TLS. New Cipher Suites for
EdDSA together with AES-GCM and ChaCha20-Poly1305 are introduced
here. This is intended to work with any version of TLS and Datagram
TLS.
Status of This Memo
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This Internet-Draft will expire on November 21, 2015.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
TLS [RFC5246] and DTLS [RFC6347] support different key exchange
algorithms and authentication mechanisms. In ECC in TLS [RFC4492],
key exchange and authentication using ECC is specified, where the
NamedCurve and ECPointFormat registries and associated TLS extensions
are introduced. In [I-D.josefsson-tls-curve25519] support for ECDHE
key exchange with the Curve25519 curve is added. That document
introduce a new NamedCurve value for Curve25519, and a new
ECPointFormat value to correspond to the public-key encoding. This
document describe how to use EdDSA and Ed25519
[I-D.josefsson-eddsa-ed25519] as a new authentication mechanism in
TLS, reusing the NamedCurve and ECPointFormat values already
introduced for Curve25519, and finally specifying new Cipher Suites
for Ed25519 with AES-GCM [RFC5288] and ChaCha20-Poly1305
[I-D.mavrogiannopoulos-chacha-tls].
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].
2. The ECDHE_EDDSA Key Exchange Algorithm
Negotiation of the authentication mechanism is signalled by sending a
SignatureAlgorithm value. Here we extend this structure for EdDSA.
enum {
eddsa(4)
} SignatureAlgorithm;
EdDSA is suitable for use with DTLS [RFC6347].
The new key exchange mechanism ECDHE_EDDSA provide forward secrecy.
The key exchange mechanism work the same way ECDHE_ECDSA but with
ECDSA replaced with EDDSA. Currently the only applicable curve is
Curve25519.
3. Cipher Suites
The following Cipher Suite values are registered, using the ChaCha20/
Poly1305 AEAD cipher described in [I-D.mavrogiannopoulos-chacha-tls]
and the AES Galois Counter Mode (GCM) cipher. The AES-GCM cipher
suites use authenticated encryption with additional data algorithms
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AEAD_AES_128_GCM and AEAD_AES_256_GCM described in [RFC5116]. GCM is
used as described in [RFC5288], but see also [RFC5289].
CipherSuite TLS_ECDHE_EDDSA_WITH_CHACHA20_POLY1305 = { 0xCC, 0xB0 }
CipherSuite TLS_ECDHE_EDDSA_WITH_AES_128_GCM_SHA256 = { 0xCC, 0xB1 }
CipherSuite TLS_ECDHE_EDDSA_WITH_AES_256_GCM_SHA256 = { 0xCC, 0xB2 }
The cipher suites are suitable for DTLS [RFC6347].
4. IANA Considerations
EdDSA should be registered in the Transport Layer Security (TLS)
Parameters [IANA-TLS] registry under "SignatureAlgorithm" as follows.
+-------+-------------+---------+-----------+
| Value | Description | DTLS-OK | Reference |
+-------+-------------+---------+-----------+
| 4 | eddsa | Y | This doc |
+-------+-------------+---------+-----------+
The follow cipher suites should be registered in the TLS Parameters
registry under "TLS Cipher Suite Registry" as follows. They should
all be marked as DTLS-OK.
CipherSuite TLS_ECDHE_EDDSA_WITH_CHACHA20_POLY1305 = { 0xCC, 0xB0 }
CipherSuite TLS_ECDHE_EDDSA_WITH_AES_128_GCM_SHA256 = { 0xCC, 0xB1 }
CipherSuite TLS_ECDHE_EDDSA_WITH_AES_256_GCM_SHA256 = { 0xCC, 0xB2 }
5. Security Considerations
The security considerations of TLS [RFC5246], DTLS [RFC6347], ECC in
TLS [RFC4492] Curve25519 in TLS [I-D.josefsson-tls-curve25519], EdDSA
and Ed25519 [I-D.josefsson-eddsa-ed25519], ChaCha20-Poly1305
[I-D.mavrogiannopoulos-chacha-tls], AES-GCM [RFC5116] an AES-GCM in
TLS [RFC5288] are inherited.
As with all cryptographic algorithms, the reader should stay informed
about new research insights into the security of the algorithms
involved.
While discussed in the EdDSA/Ed25519 specification and papers, we
would like to stress the significant of secure implementation of
EdDSA/Ed25519. For example, implementations ought to be constant-
time to avoid certain attacks.
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6. Acknowledgements
TBA.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[I-D.josefsson-tls-curve25519]
Josefsson, S. and M. Pegourie-Gonnard, "Curve25519 for
ephemeral key exchange in Transport Layer Security (TLS)",
draft-josefsson-tls-curve25519-06 (work in progress),
September 2014.
[I-D.josefsson-eddsa-ed25519]
Josefsson, S. and N. Moller, "EdDSA and Ed25519", draft-
josefsson-eddsa-ed25519-03 (work in progress), May 2015.
[I-D.mavrogiannopoulos-chacha-tls]
Langley, A., Chang, W., Mavrogiannopoulos, N.,
Strombergson, J., and S. Josefsson, "The ChaCha Stream
Cipher for Transport Layer Security", draft-
mavrogiannopoulos-chacha-tls-05 (work in progress), April
2015.
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7.2. Informative References
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
August 2008.
[IANA-TLS]
Internet Assigned Numbers Authority, "Transport Layer
Security (TLS) Parameters",
<http://www.iana.org/assignments/tls-parameters/
tls-parameters.xml>.
Author's Address
Simon Josefsson
SJD AB
Email: simon@josefsson.org
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