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Versions: 00 01                                                         
Network Working Group                                       S. Josefsson
Internet-Draft                                                    SJD AB
Intended status: Standards Track                            June 8, 2015
Expires: December 10, 2015

          EdDSA and Ed25519 for Transport Layer Security (TLS)


   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

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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   material or to cite them other than as "work in progress."

   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.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of

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Internet-Draft          EdDSA and Ed25519 for TLS              June 2015

   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 introduces a new
   NamedCurve value for Curve25519, and a new ECPointFormat value to
   correspond to the public-key encoding.

   This document describes 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

   This document is a self-contained alternative to draft-josefsson-tls-
   eddsa2.  This document specify new cipher suites for EdDSA, whereas
   draft-josefsson-tls-eddsa2 reuse the ECDSA cipher suites for EdDSA.
   It is an open issue which approach is to be prefered.

1.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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 enumeration for EdDSA.

      enum {
      } SignatureAlgorithm;

   EdDSA is suitable for use with TLS [RFC5246] and DTLS [RFC6347].

   The new key exchange mechanism ECDHE_EDDSA provides forward secrecy.
   The key exchange mechanism works just like ECDHE_ECDSA but with ECDSA

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Internet-Draft          EdDSA and Ed25519 for TLS              June 2015

   replaced with EDDSA.  Currently the only applicable curve is

   The HashAlgorithm value to specify for EdDSA MUST be "none" as the
   EdDSA signature algorithm does not hash the input before signing.

3.  Cipher Suites

   The following Cipher Suite values are registered, using the ChaCha20/
   Poly1305 authenticated encryption with additional data (AEAD) cipher
   described in [I-D.mavrogiannopoulos-chacha-tls] and the AES Galois
   Counter Mode (GCM) cipher.  The AES-GCM cipher suites use the AEAD
   algorithms AEAD_AES_128_GCM and AEAD_AES_256_GCM described in
   [RFC5116].  GCM is used as described in [RFC5288], but see also

   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_SHA384 = { 0xCC, 0xB2 }

   The cipher suites are suitable for TLS [RFC5246] and 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_SHA384 = { 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

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   [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

   While discussed in the EdDSA/Ed25519 specification and papers, we
   would like to stress the significance of secure implementation of
   EdDSA/Ed25519.  For example, implementations ought to be constant-
   time to avoid certain attacks.

6.  Acknowledgements

   Thanks to Klaus Hartke and Nicolas Williams for fixes to the

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]  Badra, M. and I. Hajjeh, "ECDHE_PSK Cipher Suites for
              Transport Layer Security (TLS)", RFC 5288, March 2009.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

              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.

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

              Langley, A., Chang, W., Mavrogiannopoulos, N.,
              Strombergson, J., and S. Josefsson, "The ChaCha Stream
              Cipher for Transport Layer Security", draft-
              mavrogiannopoulos-chacha-tls-04 (work in progress),
              December 2014.

7.2.  Informative References

   [RFC5289]  Badra, M. and I. Hajjeh, "ECDHE_PSK Cipher Suites for
              Transport Layer Security (TLS)", RFC 5289, March 2009.

              Internet Assigned Numbers Authority, "Transport Layer
              Security (TLS) Parameters",

Author's Address

   Simon Josefsson

   Email: simon@josefsson.org

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