Network Working Group J. Salowey
Request for Comments: 5288 A. Choudhury
Category: Standards Track D. McGrew
Cisco Systems, Inc.
August 2008
AES Galois Counter Mode (GCM) Cipher Suites for TLS
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
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 cipher suites that use AES-GCM with RSA, DSA, and Diffie-Hellman-based key exchange mechanisms.
RFC 5288 AES-GCM Cipher suites August 20081. Introduction
This document describes the use of AES [AES] in Galois Counter Mode (GCM) [GCM] (AES-GCM) with various key exchange mechanisms as a cipher suite for TLS. AES-GCM is an authenticated encryption with associated data (AEAD) cipher (as defined in TLS 1.2 [RFC5246]) providing both confidentiality and data origin authentication. The following sections define cipher suites based on RSA, DSA, and Diffie-Hellman key exchanges; ECC-based (Elliptic Curve Cryptography) cipher suites are defined in a separate document [RFC5289].
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 that require high data throughput can benefit from these high-speed implementations. AES-GCM has been specified as a mode that can be used with IPsec ESP [RFC4106] and 802.1AE Media Access Control (MAC) Security [IEEE8021AE].
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].
These cipher suites use the AES-GCM authenticated encryption with 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 (in particular, as described in Section 3.5 of [RFC4366], the "truncated_hmac" extension does not have an effect on cipher suites that do not use HMAC). The "nonce" SHALL be 12 bytes long consisting of two parts as follows: (this is an example of a "partially explicit" nonce; see Section 3.2.1 in [RFC5116]).
The salt is the "implicit" part of the nonce and is not sent in the packet. Instead, the salt is generated as part of the handshake process: it is either the client_write_IV (when the client is sending) or the server_write_IV (when the server is sending). The salt length (SecurityParameters.fixed_iv_length) is 4 octets.
The nonce_explicit is the "explicit" part of the nonce. It is chosen by the sender and is carried in each TLS record in the GenericAEADCipher.nonce_explicit field. The nonce_explicit length (SecurityParameters.record_iv_length) is 8 octets.
Each value of the nonce_explicit MUST be distinct for each distinct invocation of the GCM encrypt function for any fixed key. Failure to meet this uniqueness requirement can significantly degrade security. The nonce_explicit MAY be the 64-bit sequence number.
The RSA, DHE_RSA, DH_RSA, DHE_DSS, DH_DSS, and DH_anon key exchanges are performed as defined in [RFC5246].
The Pseudo Random Function (PRF) algorithms SHALL be as follows:
For cipher suites ending with _SHA256, the PRF is the TLS PRF [RFC5246] with SHA-256 as the hash function.
For cipher suites ending with _SHA384, the PRF is the TLS PRF [RFC5246] with SHA-384 as the hash function.
Implementations MUST send TLS Alert bad_record_mac for all types of failures encountered in processing the AES-GCM algorithm.
These cipher suites make use of the authenticated encryption with additional data defined in TLS 1.2 [RFC5246]. 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. Servers that 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.
Salowey, et al. Standards Track [Page 3]
RFC 5288 AES-GCM Cipher suites August 20085. IANA Considerations
IANA has assigned the following values for the cipher suites defined in this document:
The security considerations in [RFC5246] apply to this document as well. The remainder of this section describes security considerations specific to the cipher suites described in this document.
AES-GCM security requires that the counter is never reused. The IV construction in Section 3 is designed to prevent counter reuse.
Implementers should also understand the practical considerations of IV handling outlined in Section 9 of [GCM].
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 nonce_explicit used with that key is distinct. In this case, each encryption processor SHOULD include, in the nonce_explicit, a fixed value that is distinct for each processor. The recommended format is
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, the Variable field corresponds to the Counter field, and the explicit part exactly corresponds to the nonce_explicit.
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 nonce_explicit, are:
This document borrows heavily from [RFC5289]. The authors would like to thank Alex Lam, Simon Josefsson, and Pasi Eronen for providing useful comments during the review of this document.
Salowey, et al. Standards Track [Page 5]
RFC 5288 AES-GCM Cipher suites August 20088. References8.1. Normative References
[AES] National Institute of Standards and Technology,
"Advanced Encryption Standard (AES)", FIPS 197, November 2001.
[GCM] Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: Galois/Counter Mode (GCM) and GMAC", National Institute of Standards and Technology SP 800- 38D, November 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5116] McGrew, D., "An Interface and Algorithms for
Authenticated Encryption", RFC 5116, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246, August 2008.
This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org.
Salowey, et al. Standards Track [Page 8]
Ad
Translate documents to 日本語, svenska, Nederlands, Deutsch, français, русский, italiano, español, Tiếng Việt, polski, português, 中文, українська, català, norsk, فارسی, suomi, Bahasa Indonesia, العربية, čeština, 한국어, Bahasa Melayu, magyar, română, српски and other languages.
