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|
TLS Working Group J. Salowey
Internet-Draft A. Choudhury
Intended status: Standards Track D. McGrew
Expires: August 10, 2008 Cisco Systems, Inc.
February 7, 2008
AES-GCM Cipher Suites for TLS
draft-ietf-tls-rsa-aes-gcm-02
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 10, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This memo describes the use of the Advanced Encryption Standard (AES)
in Galois/Counter Mode (GCM) as a Transport Layer Security (TLS)
authenticated encryption operation. GCM provides both
confidentiality and data origin authentication, can be efficiently
implemented in hardware for speeds of 10 gigabits per second and
above, and is also well-suited to software implementations. This
memo defines TLS ciphersuites that use AES-GCM with RSA, DSS and
Salowey, et al. Expires August 10, 2008 [Page 1]
Internet-Draft AES-GCM Ciphersuites February 2008
Diffie-Hellman based key exchange mechanisms.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used In This Document . . . . . . . . . . . . . . . 3
3. AES-GCM Cipher Suites . . . . . . . . . . . . . . . . . . . . . 3
4. TLS Versions . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6.1. Counter Reuse . . . . . . . . . . . . . . . . . . . . . . . 5
6.2. Recommendations for Multiple Encryption Processors . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 9
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1. Introduction
This document describes the use of AES [AES]in Galois Counter Mode
(GCM) [GCM] (AES-GCM) with various key exchange mechanisms as a
ciphersuite for TLS. AES-GCM is not only efficient and secure, but
hardware implementations can achieve high speeds with low cost and
low latency, because the mode can be pipelined. Applications like
CAPWAP, which uses DTLS, can benefit from the high-speed
implementations when wireless termination points (WTPs) and
controllers (ACs) have to meet requirements to support higher
throughputs in the future. AES-GCM has been specified as a mode that
can be used with IPsec ESP [RFC4106] and 802.1AE MAC Security
[IEEE8021AE]. This document defines ciphersutes based on RSA, DSS
and Diffie-Hellman key exchanges; ECC based ciphersuites are defined
in a separate document [I-D.ietf-tls-ecc-new-mac]. AES-GCM is an
authenticated encryption with associated data (AEAD) cipher, as
defined in TLS 1.2 [I-D.ietf-tls-rfc4346-bis]. The ciphersuites
defined in this draft may be used with Datagram TLS defined in
[RFC4347]. This memo uses GCM in a way similar to
[I-D.ietf-tls-ecc-new-mac].
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. AES-GCM Cipher Suites
The following ciphersuites use the new authenticated encryption modes
defined in TLS 1.2 with AES in Galois Counter Mode (GCM) [GCM]:
CipherSuite TLS_RSA_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_RSA_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DH_RSA_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DH_RSA_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DHE_DSS_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DH_DSS_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DH_DSS_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DH_anon_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DH_anon_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
These ciphersuites use the AES-GCM authenticated encryption with
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associated data (AEAD) algorithms AEAD_AES_128_GCM and
AEAD_AES_256_GCM described in [RFC5116]. Note that each of these
AEAD algorithms uses a 128-bit authentication tag with GCM. The
"nonce" SHALL be 12 bytes long and it is "partially implicit" (see
section 3.2.1 in [RFC5116]). Part of the nonce is generated as part
of the handshake process and is static for the entire session and the
other part is carried in each packet.
Struct{
opaque salt[4];
opaque explicit_nonce_part[8];
} GCMNonce
The salt is the "implicit" part of the nonce and is not sent in the
packet. It is either the client_write_IV if the client is sending or
the server_write_IV if the server is sending. These IVs SHALL be 4
bytes long, therefore, for all the algorithms defined in this
section, SecurityParameters.fixed_iv_length=4.
The explicit_nonce_part is chosen by the sender and included in the
packet. Each value of the explicit_nonce_part MUST be distinct for
each distinct invocation of GCM encrypt function for any fixed key.
Failure to meet this uniqueness requirement can significantly degrade
security. The explicit_nonce_part is carried in the IV field of the
GenericAEADCipher structure. For all the algorithms defined in this
section, SecurityParameters.record_iv_length=8.
In the case of TLS the explicit_nonce_part MAY be the 64-bit sequence
number. In the case of Datagram TLS [RFC4347] the
explicit_nonce_part MAY be formed from the concatenation of the 16-
bit epoch with the 48-bit DTLS seq_num.
The RSA, DHE_RSA, DH_RSA, DHE_DSS, DH_DSS, and DH_anon key exchanges
are performed as defined in [I-D.ietf-tls-rfc4346-bis].
The PRF algorithms SHALL be as follows:
For ciphersuites ending in _SHA256 the hash function is SHA256.
For ciphersuites ending in _SHA384 the hash function is SHA384.
4. TLS Versions
These ciphersuites make use of the authenticated encryption with
additional data defined in TLS 1.2 [I-D.ietf-tls-rfc4346-bis]. They
MUST NOT be negotiated in older versions of TLS. Clients MUST NOT
offer these cipher suites if they do not offer TLS 1.2 or later.
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Servers which select an earlier version of TLS MUST NOT select one of
these cipher suites. Because TLS has no way for the client to
indicate that it supports TLS 1.2 but not earlier, a non-compliant
server might potentially negotiate TLS 1.1 or earlier and select one
of the cipher suites in this document. Clients MUST check the TLS
version and generate a fatal "illegal_parameter" alert if they detect
an incorrect version.
5. IANA Considerations
IANA has assigned the following values for the ciphersuites defined
in this draft:
CipherSuite TLS_RSA_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_RSA_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DH_RSA_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DH_RSA_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DHE_DSS_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DH_DSS_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DH_DSS_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
CipherSuite TLS_DH_anon_WITH_AES_128_GCM_SHA256 = {TBD,TBD}
CipherSuite TLS_DH_anon_WITH_AES_256_GCM_SHA384 = {TBD,TBD}
6. Security Considerations
The security considerations in [I-D.ietf-tls-rfc4346-bis] apply to
this document as well. The remainder of this section describes
security considerations specific to the cipher suites described in
this document.
6.1. Counter Reuse
AES-GCM security requires that the counter is never reused. The IV
construction in Section 3 is designed to prevent counter reuse.
6.2. Recommendations for Multiple Encryption Processors
If multiple cryptographic processors are in use by the sender, then
the sender MUST ensure that, for a particular key, each value of the
explicit_nonce_part used with that key is distinct. In this case
each encryption processor SHOULD include in the explicit_nonce_part a
fixed value that is distinct for each processor. The recommended
format is
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Internet-Draft AES-GCM Ciphersuites February 2008
explicit_nonce_part = FixedDistinct || Variable
where the FixedDistinct field is distinct for each encryption
processor, but is fixed for a given processor, and the Variable field
is distinct for each distinct nonce used by a particular encryption
processor. When this method is used, the FixedDistinct fields used
by the different processors MUST have the same length.
In the terms of Figure 2 in [RFC5116], the Salt is the Fixed-Common
part of the nonce (it is fixed, and it is common across all
encryption processors), the FixedDistinct field exactly corresponds
to the Fixed-Distinct field, and the Variable field corresponds to
the Counter field, and the explicit part exactly corresponds to the
explicit_nonce_part.
For clarity, we provide an example for TLS in which there are two
distinct encryption processors, each of which uses a one-byte
FixedDistinct field:
Salt = eedc68dc
FixedDistinct = 01 (for the first encryption processor)
FixedDistinct = 02 (for the second encryption processor)
The GCMnonces generated by the first encryption processor, and their
corresponding explicit_nonce_parts, are:
GCMNonce explicit_nonce_part
------------------------ ----------------------------
eedc68dc0100000000000000 0100000000000000
eedc68dc0100000000000001 0100000000000001
eedc68dc0100000000000002 0100000000000002
...
The GCMnonces generated by the second encryption processor, and their
corresponding explicit_nonce_parts, are
GCMNonce explicit_nonce_part
------------------------ ----------------------------
eedc68dc0200000000000000 0200000000000000
eedc68dc0200000000000001 0200000000000001
eedc68dc0200000000000002 0200000000000002
...
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7. Acknowledgements
This draft borrows heavily from [I-D.ietf-tls-ecc-new-mac]. The
authors would like to thank Alex Lam and Pasi Eronen for providing
useful comments during the review of this draft.
8. References
8.1. Normative References
[AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard
(AES)", FIPS 197, November 2001.
[GCM] National Institute of Standards and Technology,
"Recommendation for Block Cipher Modes of Operation:
Galois Counter Mode (GCM) for Confidentiality and
Authentication", SP 800-38D, April 2006.
[I-D.ietf-tls-rfc4346-bis]
Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", draft-ietf-tls-rfc4346-bis-08
(work in progress), January 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 2008.
8.2. Informative References
[I-D.ietf-tls-ecc-new-mac]
Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode",
draft-ietf-tls-ecc-new-mac-02 (work in progress),
December 2007.
[IEEE8021AE]
Institute of Electrical and Electronics Engineers, "Media
Access Control Security", IEEE Standard 802.1AE,
August 2006.
[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
Salowey, et al. Expires August 10, 2008 [Page 7]
Internet-Draft AES-GCM Ciphersuites February 2008
(GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 4106, June 2005.
Authors' Addresses
Joseph Salowey
Cisco Systems, Inc.
2901 3rd. Ave
Seattle, WA 98121
USA
Email: jsalowey@cisco.com
Abhijit Choudhury
Cisco Systems, Inc.
3625 Cisco Way
San Jose, CA 95134
USA
Email: abhijitc@cisco.com
David McGrew
Cisco Systems, Inc.
170 W Tasman Drive
San Jose, CA 95134
USA
Email: mcgrew@cisco.com
Salowey, et al. Expires August 10, 2008 [Page 8]
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Salowey, et al. Expires August 10, 2008 [Page 9]
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