Internet DRAFT - draft-josefsson-tls-additional-curves
draft-josefsson-tls-additional-curves
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
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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.
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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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