Network Working Group M. Salter
Internet-Draft National Security Agency
Intended status: Informational E. Rescorla
Expires: December 4, 2007 Network Resonance
June 2, 2007
Suite B Cipher Suites for TLS
draft-rescorla-tls-suiteb-01.txt
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Copyright (C) The IETF Trust (2007).
Abstract
The United States Government has published guidelines for "NSA Suite
B Cryptography" dated July, 2005, which defines cryptographic
algorithm polcy for national security applications. This document
defines a profile of TLS which is conformant with Suite B.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used In This Document . . . . . . . . . . . . . . . 3
3. Suite B Requirements . . . . . . . . . . . . . . . . . . . . . 3
4. Suite B Compliance Requirements . . . . . . . . . . . . . . . . 4
4.1. Security Levels . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Acceptable Curves . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Introduction
In July, 2005 the National Security Agency posted "Fact Sheet, NSA
Suite B Cryptography" which stated:
To complement the existing policy for the use of the Advanced
Encryption Standard (AES) to protect national security systems
and information as specified in The National Policy on the use of
the Advanced Encryption Standard (AES) to Protect National
Security Systems and National Security Information (CNSSP-15),
the National Security Agency (NSA) announced Suite B Cryptography
at the 2005 RSA Conference. In addition to the AES, Suite B
includes cryptographic algorithms for hashing, digital
signatures, and key exchange.
Suite B only specifies the cryptographic algorithms to be
used. Many other factors need to be addressed in determining
whether a particular device implementing a particular set of
cryptographic algorithms should be used to satisfy a particular
requirement.
Among those factors are "requirements for interoperability both
domestically and internationally".
This document is a profile of of TLS 1.2 [I-D.ietf-tls-rfc4346-bis]
and of the cipher suites defined in [I-D.ietf-tls-ecc-new-mac], but
does not itself define any new cipher suites. This profile requires
TLS 1.2.
2. 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].
3. Suite B Requirements
The "Suite B Fact Sheet" requires that key establishment and
authentication algorithms be based on Elliptic Curve Cryptography,
that the encryption algorithm be AES [AES], and that the function
used for key derivation and data integrity be SHA [SHS]. It defines
two security levels, of 128 and 192 bits.
In particular it states:
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SUITE B includes:
Encryption: Advanced Encryption Standard (AES) -
FIPS 197 (with keys sizes of 128 and 256
bits)
Digital Signature: Elliptic Curve Digital Signature Algorithm -
FIPS 186-2 (using the curves with 256 and
384-bit prime moduli)
Key Exchange: Elliptic Curve Diffie-Hellman or Elliptic
Curve MQV Draft NIST Special Publication
800-56 (using the curves with 256 and
384-bit prime moduli)
Hashing: Secure Hash Algorithm - FIPS 180-2
(using SHA-256 and SHA-384)
All implementations of Suite B must, at a minimum, include AES
with 128-bit keys, the 256-bit prime modulus elliptic curve and
SHA-256 as a common mode for widespread interoperability.
The 128-bit security level corresponds to an elliptic curve size of
256 bits, AES-128, and SHA-256. The 192-bit security level
corresponds to an elliptic curve size of 384 bits, AES-256, and SHA-
384.
4. Suite B Compliance Requirements
To be considered "Suite B compatible" at least one of the Galois
Counter Mode (GCM) CipherSuites defined in [I-D.ietf-tls-ecc-new-mac]
MUST be negotiated. In compliance with the guidance in the Suite B
Fact Sheet every TLS implementation of Suite B SHOULD implement
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256.
4.1. Security Levels
As described in Section 1, Suite B specifies two security levels, 128
and 192 bit. The following table lists the security levels for each
cipher suite:
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+-----------------------------------------+----------------+
| Cipher Suite | Security Level |
+-----------------------------------------+----------------+
| TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 | 128 |
| TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256 | 128 |
| TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 | 192 |
| TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384 | 192 |
+-----------------------------------------+----------------+
4.2. Acceptable Curves
RFC 4492 defines a variety of elliptic curves. For cipher suites
defined in this specification, only secp256r1 (23) or secp384r1 (24)
may be used. (These are the same curves that appear in FIPS 186-2 as
P-256 and P-384, respectively.) For cipher suites at the 128-bit
security level, secp256r1 MUST be used. For cipher suites at the
192-bit security level, secp384r1 MUST be used. RFC 4492 requires
that uncompressed (0) form be supported. ansiX962_compressed_prime(1)
point formats MAY be supported.
Clients desiring to negotiate only a Suite B-compliant connection
MUST generate a "Supported Elliptic Curves Extension" containing only
the allowed curves. These curves MUST match the cipher suite
security levels being offered. Clients which are willing to do both
Suite B-compliant and non-Suite B-compliant connections MAY omit the
extension or send the extension but offer other curves as well as the
appropriate Suite B ones.
Servers desiring to negotiate a Suite B-compliant connection SHOULD
check for the presence of the extension, but MUST NOT negotiate
inappropriate curves even if they are offered by the client. This
allows a Client which is willing to do either Suite B-compliant or
non-Suite B-compliant modes to interoperate with a server which will
only do Suite B-compliant modes. If the client does not advertise an
acceptable curve, the server MUST generate a fatal
"handshake_failure" alert and terminate the connection. Clients MUST
check the chosen curve to make sure it is acceptable.
5. Security Considerations
Most of the security considerations for this document are described
in TLS 1.2 [I-D.ietf-tls-rfc4346-bis], RFC 4492 [RFC4492], and
[I-D.ietf-tls-ecc-new-mac]. Readers should consult those documents.
In order to meet the goal of a consistent security level for the
entire cipher suite, in Suite B mode TLS implementations MUST ONLY
use the curves defined in Section 4.2. Otherwise, it is possible to
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have a set of symmetric algorithms with much weaker or stronger
security properties than the asymmetric (ECC) algorithms.
6. IANA Considerations
This document defines no actions for IANA.
7. Acknowledgements
This work was supported by the US Department of Defense.
8. References
8.1. 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.
[I-D.ietf-tls-rfc4346-bis]
Dierks, T. and E. Rescorla, "The TLS Protocol Version
1.2", draft-ietf-tls-rfc4346-bis-03 (work in progress),
March 2007.
[AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard
(AES)", FIPS 197, November 2001.
[SHS] National Institute of Standards and Technology, "Secure
Hash Standard", FIPS 180-2, August 2002.
[I-D.ietf-tls-ecc-new-mac]
Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode", April 2007.
8.2. Informative References
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Authors' Addresses
Margaret Salter
National Security Agency
9800 Savage Rd.
Fort Meade 20755-6709
USA
Email: msalter@restarea.ncsc.mil
Eric Rescorla
Network Resonance
2483 E. Bayshore #212
Palo Alto 94303
USA
Email: ekr@networkresonance.com
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