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Network Working Group                                       S. Josefsson
Internet-Draft                                                    SJD AB
Updates: 4492 (if approved)                          M. Pegourie-Gonnard
Intended status: Informational                    Independant / PolarSSL
Expires: March 15, 2015                               September 11, 2014


   Additional Elliptic Curves for Transport Layer Security (TLS) Key
                               Agreement
                draft-josefsson-tls-additional-curves-01

Abstract

   This document specifies the use of additional elliptic curves (M-221,
   E-222, Curve1174, E-382, M-383, Curve383187, Curve41417,
   Ed448-Goldilocks, M-511, and E-521) for key exchange in the Transport
   Layer Security (TLS) protocol.  As such it updates RFC 4492.

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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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 15, 2015.

Copyright Notice

   Copyright (c) 2014 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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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Introduction

   In [SafeCurves] and [I-D.ladd-safecurves] additional elliptic curves
   are described that have performance and security advantages, of
   different strengths, for uses that may include key agreement.  The
   complete list of curves is M-221 (aka Curve2213), E-222, Curve1174,
   E-382, M-383, Curve383187, Curve41417 (aka Curve3617),
   Ed448-Goldilocks, M-511 (aka Curve511187), and E-521.  In this
   document we refer to that list of curves informally as "additional
   safe curves" or simply "additional curves".

   Note that Curve25519 is excluded from this document since it is
   covered in [I-D.josefsson-tls-curve25519].  These two drafts may
   eventually be merged.  Currently the Curve25519 draft is more mature
   and ready for implementation, whereas this draft is more food for
   discussion.

   [RFC4492] defines the usage of elliptic curves for authentication and
   key agreement in TLS 1.0 and TLS 1.1, and these mechanisms are also
   applicable to TLS 1.2 [RFC5246].  The use of ECC curves for key
   exchange requires the definition and assignment of additional
   NamedCurve IDs.  This document specify that value for the additional
   curves, as well as the minor changes in key selection and
   representation that are required to accommodate for the curves
   slightly different nature.

   This document only describes usage of additional curves for ephemeral
   key exchange (ECDHE), not for use with long-term keys embedded in
   PKIX certificates (ECDH_RSA and ECDH_ECDSA).  This is because the
   additional curves are not directly suitable for authentication with
   ECDSA, and thus not applicable for signing of e.g.  PKIX
   certificates.

2.  New NamedCurve type

   Curve negotiation is the same for the additional curves as for other
   curves, but is restricted to using the named_curve type in the
   ServerKeyEchange message: the explicit_prime type is only suited to
   curves in short Weierstrass form.  This document adds a new
   NamedCurve value for the additional curves as follows.








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         enum {
           M221(TBD1),
           E222(TBD2),
           Curve1174(TBD3),
           E382(TBD4),
           M383(TBD5),
           Curve383187(TBD6),
           Curve41417(TBD7),
           Ed448-Goldilocks(TBD8),
           M511(TBD9),
           E521(TBD10)
         } NamedCurve;

   The curves are suitable for use with DTLS [RFC6347].

   Since these curves are not designed to be used in signatures, clients
   who offer ECDHE_ECDSA ciphersuites and advertise support for any of
   these curves in the elliptic_curves ClientHello extension SHOULD also
   advertise support for at least one other curve, suitable for ECDSA.
   Servers MUST NOT select an ECDHE_ECDSA ciphersuite if the only common
   curve is one of these curves.

3.  Acknowledgement

   This document was inspired by the content and structure of [RFC7027].

4.  IANA Considerations

   IANA is requested to assign numbers for the additional curves listed
   in Section 2 to the Transport Layer Security (TLS) Parameters
   registry EC Named Curve [IANA-TLS] as follows.




















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            +-------+------------------+---------+-----------+
            | Value |   Description    | DTLS-OK | Reference |
            +-------+------------------+---------+-----------+
            |  TBD1 |       M221       |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD2 |       E222       |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD3 |    Curve1174     |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD4 |       E382       |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD5 |       M383       |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD6 |   Curve383187    |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD7 |    Curve41417    |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD8 | Ed448-Goldilocks |    Y    |  This doc |
            |       |                  |         |           |
            |  TBD9 |       M511       |    Y    |  This doc |
            |       |                  |         |           |
            | TBD10 |       E521       |    Y    |  This doc |
            +-------+------------------+---------+-----------+

                                  Table 1

5.  Security Considerations

   The security considerations of [RFC5246] and most of the security
   considerations of [RFC4492] apply accordingly.

   See also [SafeCurves] and [I-D.ladd-safecurves] for more security
   discussions.

6.  References

6.1.  Normative References

   [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.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

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




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   [I-D.ladd-safecurves]
              Ladd, W., "Additional Elliptic Curves for IETF protocols",
              draft-ladd-safecurves-04 (work in progress), March 2014.

6.2.  Informative References

   [RFC7027]  Merkle, J. and M. Lochter, "Elliptic Curve Cryptography
              (ECC) Brainpool Curves for Transport Layer Security
              (TLS)", RFC 7027, October 2013.

   [I-D.josefsson-tls-curve25519]
              Josefsson, S. and M. Pegourie-Gonnard, "Curve25519 for
              ephemeral key exchange in Transport Layer Security (TLS)",
              draft-josefsson-tls-curve25519-05 (work in progress),
              April 2014.

   [IANA-TLS]
              Internet Assigned Numbers Authority, "Transport Layer
              Security (TLS) Parameters",
              <http://www.iana.org/assignments/tls-parameters/
              tls-parameters.xml>.

   [SafeCurves]
              Bernstein, D. and T. Lange, "SafeCurves: choosing safe
              curves for elliptic-curve cryptography.", January 2014,
              <http://safecurves.cr.yp.to/>.

Authors' Addresses

   Simon Josefsson
   SJD AB

   Email: simon@josefsson.org


   Manuel Pegourie-Gonnard
   Independant / PolarSSL

   Email: mpg@elzevir.fr












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