TLS Working Group P. Gutmann
Internet-Draft University of Auckland
Intended status: Standards Track April 24, 2011
Expires: October 26, 2011
Standardised ECC Cipher Suites for TLS
draft-gutmann-tls-eccsuites-00.txt
Abstract
This document describes a set of standard ECC cipher suites for TLS
that simplify the complex selection procedure described in the
existing ECC RFC, simplifying implementation and easing
interoperability problems.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . . 3
2. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
5. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
[TLS-ECC] provides an extremely flexible, and by extension extremely
complex means of specifying a large number of options involving the
use of ECC algorithms for [TLS]. As such the "cipher suites" in
[TLS-ECC] aren't suites in the conventional TLS sense but more an
indication of intent to negotiate a Chinese menu, with details to be
decided on later via various TLS extensions and parameter settings.
This makes deciding on a particular suite nondeterministic, since
later parameter choices and settings can negate the initial "cipher
suite" choice, requiring returning to the suite list to try with
another Chinese-menu suite in the hope that later parameter choices
allow it to be used.
In practice no deployed implementation actually does this, either
dropping the connection or aborting the handshake with a handshake-
failure if the expected parameters aren't present throughout the
various locations in the TLS handshake in which ECC parameters can be
specified. This means that establishing a TLS connection using ECC
often requires trial-and-error probing to ascertain what the other
side is expecting to see before a connection can be established.
Experience with deployed implementations indicates that all of them
appear to implement a common subset of fixed ECC parameters that work
in all cases (alongside the more obscure options), representing a de
facto profile of standard cipher suites rather than Chinese-menu
selection options. This document standardises this de facto usage by
defining a small number of standard ECC cipher suites with
unambiguous parameters and settings.
1.1. Conventions Used in This Document
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].
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2. Cipher Suites
The table below defines standard ECC cipher suites with fixed,
unambiguous parameters, based on the de facto profiles of suites seen
in use in practice. Since the form of these suites match the
existing non-ECC suites, they follow the existing suites in the {
0x00, 0xXX } range rather than being placed with the Chinese-menu-
selection suites at { 0xC0, 0xXX }.
CipherSuite TLS_ECDHE_ECDSA_P256_WITH_AES_128_CBC_SHA = { 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P256_WITH_AES_256_CBC_SHA = { 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P384_WITH_AES_128_CBC_SHA = { 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P384_WITH_AES_256_CBC_SHA = { 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P256_WITH_AES_128_CBC_SHA256 =
{ 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P256_WITH_AES_256_CBC_SHA256 =
{ 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P384_WITH_AES_128_CBC_SHA384 =
{ 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P384_WITH_AES_256_CBC_SHA384 =
{ 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P256_WITH_AES_128_GCM_SHA256 =
{ 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P256_WITH_AES_256_GCM_SHA256 =
{ 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P384_WITH_AES_128_GCM_SHA384 =
{ 0x00, 0xXX }
CipherSuite TLS_ECDHE_ECDSA_P384_WITH_AES_256_GCM_SHA384 =
{ 0x00, 0xXX }
[[[At least one major implementation, Microsoft's SChannel, already
does this, see
<http://msdn.microsoft.com/en-us/library/aa374757%28v=vs.85%29.aspx>.
For example it lists 'suites' like
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256_P256 and
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256_P256. The above choices
happen to coincide with the Microsoft ones not because of any
explicit attempt to copy the Microsoft options but because they
represent the obvious, logical choices]]].
For each cipher suite with their ECC parameters denoted 'P256' or
'P384', the ECC parameters are:
o ECDH key agreement in Server Key Exchange/Client Key Exchange
message: NIST P-256/X9.62 p256r1/SECG p256r1 or NIST P-384/SECG
p384r1 curve with uncompressed points as indicated in the suite
name.
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o ECDSA signature in Server Key Exchange message: P256 or P384 curve
as for ECDH with uncompressed points and SHA1, SHA256 or SHA384 as
indicated in the suite name.
o Client authentication in Certificate Request/Certificate Verify
messages: SHA1, SHA256, or SHA384 as indicated in the suite name.
If no additional Chinese-menu ECC suites are used, implementations
SHOULD NOT send the Supported Elliptic Curves or Supported Point
Formats extensions since these parameters are fully specified by the
suite choice. If additional Chinese-menu suites are used,
implementations MUST send the Supported Elliptic Curves and Supported
Point Formats extensions as per [TLS-ECC]. The parameters specified
in these extensions apply only to the Chinese-menu suites, not the
fixed suites defined above.
Note that the suites defined in this document augment, rather than
supplant, the existing Chinese-menu suites options. Anyone requiring
the use of more unusual ECC parameters and options can use the
Chinese-menu capability to specify and select any parameters that
they require.
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3. Security Considerations
This document is a profile of, and simplifcation of, [TLS-ECC]. No
further security considerations are introduced beyond those present
in [TLS-ECC] .
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4. IANA Considerations
This document defines new ciphers suites for TLS [to be allocated in
the currently unallocated range { 0x00, 0xC6 } - { 0x00, 0xD1 }].
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5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[TLS-ECC] Blake-Wilson, S., Bolyard, N., Gupta, V., and C. Hawk,
"Elliptic Curve Cryptography (ECC) Cipher Suites for
Transport Layer Security (TLS)", RFC 4492, May 2006.
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Author's Address
Peter Gutmann
University of Auckland
Department of Computer Science
New Zealand
Email: pgut001@cs.auckland.ac.nz
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