TLS Working Group M. Badra
Internet-Draft LIMOS Laboratory
Intended status: Informational
Expires: June 2008 November 2007
ECDHE_PSK Ciphersuites for TLS
<draft-badra-ecdhe-tls-psk-01.txt>
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document updates RFC 4785 and RFC 4279 and specifies a set of
ciphersuites that use an Elliptic Curve Diffie-Hellman exchange
authenticated with a pre-shared key. These ciphersuites provides
Perfect Forward Secrecy. It specifies as well one authentication-
only ciphersuites (with no encryption). This ciphersuite is useful
when authentication and integrity protection is desired, but
confidentiality is not needed or not permitted.
The reader is expected to become familiar with RFC 4785 and RFC 4279
prior to studying this document.
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1. Introduction
RFC 4279 specifies ciphersuites for supporting TLS using pre-shared
symmetric keys and they (a) use only symmetric key operations for
authentication, (b) use a Diffie-Hellman exchange authenticated with
a pre-shared key, or (c) combines public key authentication of the
server with pre-shared key authentication of the client.
RFC 4785 specifies authentication-only ciphersuites (with no
encryption).
This document specifies a set of ciphersuites that use an Elliptic
Curve Diffie-Hellman exchange authenticated with a pre-shared key.
These ciphersuites provides Perfect Forward Secrecy. It specifies as
well one authentication-only ciphersuites (with no encryption). This
ciphersuite is useful when authentication and integrity protection
is desired, but confidentiality is not needed or not permitted.
2. Updating RFC4279
The new ciphersuites proposed here match the ciphersuites defined in
[RFC4279], except that they use an Elliptic Curve Diffie-Hellman
exchange [RFC4492] authenticated with a pre-shared key. They are
defined as follow:
CipherSuite Key Exchange Cipher Hash
TLS_ECDHE_PSK_WITH_RC4_128_SHA ECDHE_PSK RC4_128 SHA
TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA ECDHE_PSK 3DES_EDE_CBC SHA
TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA ECDHE_PSK AES_128_CBC SHA
TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA ECDHE_PSK AES_256_CBC SHA
When these ciphersuites are used, the ServerKeyExchange and
ClientKeyExchange messages also include the Diffie-Hellman
parameters. The PSK identity and identity hint fields have the same
meaning as in the previous section (note that the ServerKeyExchange
message is always sent, even if no PSK identity hint is provided).
The format of the ServerKeyExchange and ClientKeyExchange messages
is shown below.
struct {
select (KeyExchangeAlgorithm) {
/* other cases for rsa, diffie_hellman, etc. */
case ec_diffie_hellman_psk: /* NEW */
opaque psk_identity_hint<0..2^16-1>;
ServerECDHParams params;
};
} ServerKeyExchange;
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struct {
select (KeyExchangeAlgorithm) {
/* other cases for rsa, diffie_hellman, etc. */
case ec_diffie_hellman_psk: /* NEW */
opaque psk_identity<0..2^16-1>;
ClientECDiffieHellmanPublic public;
} exchange_keys;
} ClientKeyExchange;
The premaster secret is formed as follows. First, perform the
Elliptic Curve Diffie-Hellman computation in the same way as for
other Diffie-Hellman-based ciphersuites in [TLS1.0] or [TLS1.1]. Let
Z be the value produced by this computation. Concatenate a uint16
containing the length of Z (in octets), Z itself, a uint16
containing the length of the PSK (in octets), and the PSK itself.
This corresponds to the general structure for the premaster secrets
(see Note 1 in Section 2 in RFC 4279) in [RFC4279], with
"other_secret" containing Z:
struct {
opaque other_secret<0..2^16-1>;
opaque psk<0..2^16-1>;
};
Here "other_secret" comes from the Elliptic Curve Diffie-Hellman
exchange (ECDHE_PSK).
3. Updating RFC4785
The new ciphersuite proposed here match the ciphersuites defined in
[RFC4785], except that it uses an Elliptic Curve Diffie-Hellman
exchange authenticated with a pre-shared key
CipherSuite Key Exchange Cipher Hash
TLS_ECDHE_PSK_WITH_NULL_SHA ECDHE_PSK NULL SHA
4. Security Considerations
The security considerations described throughout [TLS1.0],
[TLSv1.1], RFC 4785 and RFC 4279 apply here as well.
5. IANA Considerations
This document defines the following new ciphersuites, whose values
are to be assigned from the TLS Cipher Suite registry defined in
[TLS1.1].
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CipherSuite TLS_ECDHE_PSK_WITH_RC4_128_SHA = { 0xXX, 0xXX };
CipherSuite TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA = { 0xXX, 0xXX };
CipherSuite TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA = { 0xXX, 0xXX };
CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA = { 0xXX, 0xXX };
CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA = { 0xXX, 0xXX };
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[TLS1.0] T., Dierks, C., Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[TLS1.1] Dierks, T., Rescorla, E., "The TLS Protocol Version 1.1",
RFC 4346, April 200P.
[RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
for Transport Layer Security (TLS)", RFC 4279, December
2005.
[RFC4785] Blumenthal, U., Goel, P., "Pre-Shared Key (PSK)
Ciphersuites with NULL Encryption for Transport Layer
Security (TLS)", RFC 4785, January 2007.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C.,
Moeller, B., "Elliptic Curve Cryptography (ECC) Cipher
Suites for Transport Layer Security (TLS)", RFC 4492, May
2006.
Acknowledgements
The authors would like to thank Bodo Moeller for comments on the
document.
Author's Addresses
Mohamad Badra
LIMOS Laboratory - UMR (6158), CNRS
France Email: badra@isima.fr
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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