TLS Working Group Mohamad Badra Internet Draft LIMOS Laboratory Intended status: Standards Track March 29, 2008 Expires: September 2008 Pre-Shared Key Cipher Suites for Transport Layer Security with SHA-256/384 and AES Galois Counter Mode draft-badra-tls-psk-new-mac-aes-gcm-01.txt 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 September 29, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract RFC 4279 and RFC 4785 describe pre-shared key cipher suites for Transport Layer Security (TLS). However, all those cipher suites use SHA-1 as their MAC algorithm. This document describes a set of cipher suites for TLS/DTLS which uses stronger digest algorithms Badra Expires September 29, 2008 [Page 1] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 (i.e. SHA-256 or SHA-384) and another which uses AES in Galois Counter Mode (GCM). Table of Contents 1. Introduction...................................................3 1.1. Conventions used in this document.........................3 2. PSK, DHE_PSK and RSA_PSK Key Exchange Algorithms with AES-GCM..3 3. PSK, DHE_PSK and RSA_PSK Key Exchange with SHA-256/384.........4 3.1. PSK Key Exchange Algorithm with SHA-256/384...............4 3.2. DHE_PSK Key Exchange Algorithm with SHA-256/384...........5 3.3. RSA_PSK Key Exchange Algorithm with SHA-256/384...........5 4. TLS Versions...................................................6 5. Security Considerations........................................6 5.1. Counter Reuse with GCM....................................6 5.2. Recommendations for Multiple Encryption Processors........6 6. IANA Considerations............................................7 7. Acknowledgments................................................8 8. References.....................................................8 8.1. Normative References......................................8 8.2. Informative References....................................9 Author's Addresses................................................9 Intellectual Property Statement..................................10 Disclaimer of Validity...........................................10 Badra Expires September 29, 2008 [Page 2] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 1. Introduction This document describes the use of AES [AES] in Galois Counter Mode (GCM) [GCM] (AES-GCM) with various pre-shared key (PSK) key exchange mechanisms ([RFC4279] and [RFC4785]) as a ciphersuite for Transport Layer Security (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. This document also specifies PSK cipher suites for TLS which replace SHA-256 and SHA-384 rather than SHA-1. RFC 4279 [RFC4279] and RFC 4785 [RFC4785] describe pre-shared key (PSK) cipher suites for TLS. However, all of the RFC 4279 and the RFC 4785 suites use HMAC-SHA1 as their MAC algorithm. Due to recent analytic work on SHA-1 [Wang05], the IETF is gradually moving away from SHA-1 and towards stronger hash algorithms. [I-D.ietf-tls-ecc-new-mac] and [I-D.ietf-tls-rsa-aes-gcm] provide support for GCM with other key establishment methods. 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]. 2. PSK, DHE_PSK and RSA_PSK Key Exchange Algorithms with AES-GCM The following eight cipher suites use the new authenticated encryption modes defined in TLS 1.2 with AES in Galois Counter Mode (GCM) [GCM]: CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_258_GCM_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA384 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_256_GCM_SHA384 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_128_GCM_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_256_GCM_SHA384 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_128_GCM_SHA256 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_256_GCM_SHA384 = {0xXX,0xXX}; These cipher suites use authenticated encryption with additional data algorithms AEAD_AES_128_GCM and AEAD_AES_256_GCM described in RFC 5116. The "nonce" input to the AEAD algorithm SHALL be 12 bytes long, and is "partially implicit" (see Section 3.2.1 of RFC 5116). Part of the nonce is generated as part of the handshake process and is static for the entire session and part is carried in each packet. Badra Expires September 29, 2008 [Page 3] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 struct { opaque salt[4]; opaque explicit_nonce_part[8]; } GCMNonce. The salt value 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 from all other values, 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. Therefore, for all the algorithms defined in this section, SecurityParameters.record_iv_length=8. In the case of TLS the counter MAY be the 64-bit sequence number. In the case of Datagram TLS [RFC4347] the counter MAY be formed from the concatenation of the 16-bit epoch with the 48-bit sequence number. 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. 3. PSK, DHE_PSK and RSA_PSK Key Exchange with SHA-256/384 The cipher suites described in this section use AES [AES] in CBC [CBC] mode with an HMAC-based MAC. 3.1. PSK Key Exchange Algorithm with SHA-256/384 CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_NULL_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_NULL_SHA384 = {0xXX,0xXX}; The above six cipher suites are the same as the corresponding cipher suites in RFC 4279 and RFC 4785 (TLS_PSK_WITH_AES_128_CBC_SHA, TLS_PSK_WITH_AES_256_CBC_SHA, and TLS_PSK_WITH_NULL_SHA) except for Badra Expires September 29, 2008 [Page 4] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 the hash and PRF algorithms, which are SHA-256 and SHA-384 [SHS] as follows. Cipher Suite MAC PRF ------------ --- --- TLS_PSK_WITH_AES_128_CBC_SHA256 HMAC-SHA-256 P_SHA-256 TLS_PSK_WITH_AES_128_CBC_SHA384 HMAC-SHA-384 P_SHA-384 TLS_PSK_WITH_AES_256_CBC_SHA256 HMAC-SHA-256 P_SHA-256 TLS_PSK_WITH_AES_256_CBC_SHA384 HMAC-SHA-384 P_SHA-384 TLS_PSK_WITH_NULL_SHA256 HMAC-SHA-256 P_SHA-256 TLS_PSK_WITH_NULL_SHA384 HMAC-SHA-384 P_SHA-384 3.2. DHE_PSK Key Exchange Algorithm with SHA-256/384 CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_NULL_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_NULL_SHA384 = {0xXX,0xXX}; The above six cipher suites are the same as the corresponding cipher suites in RFC 4279 and RFC 4785 (TLS_DHE_PSK_WITH_AES_128_CBC_SHA, TLS_DHE_PSK_WITH_AES_256_CBC_SHA, and TLS_DHE_PSK_WITH_NULL_SHA) except for the hash and PRF algorithms, which are SHA-256 and SHA- 384 [SHS] as follows. Cipher Suite MAC PRF ------------ --- --- TLS_DHE_PSK_WITH_AES_128_CBC_SHA256 HMAC-SHA-256 P_SHA-256 TLS_DHE_PSK_WITH_AES_128_CBC_SHA384 HMAC-SHA-384 P_SHA-384 TLS_DHE_PSK_WITH_AES_256_CBC_SHA256 HMAC-SHA-256 P_SHA-256 TLS_DHE_PSK_WITH_AES_256_CBC_SHA384 HMAC-SHA-384 P_SHA-384 3.3. RSA_PSK Key Exchange Algorithm with SHA-256/384 CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA384 = {0xXX,0xXX}; The above four cipher suites are the same as the corresponding cipher suites in RFC 4279 and RFC 4785 (TLS_RSA_PSK_WITH_AES_128_CBC_SHA, TLS_RSA_PSK_WITH_AES_256_CBC_SHA, and TLS_RSA_PSK_WITH_NULL_SHA) except for the hash and PRF algorithms, which are SHA-256 and SHA-384 [SHS] as follows. Badra Expires September 29, 2008 [Page 5] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 Cipher Suite MAC PRF ------------ --- --- TLS_RSA_PSK_WITH_AES_128_CBC_SHA256 HMAC-SHA-256 P_SHA-256 TLS_RSA_PSK_WITH_AES_128_CBC_SHA384 HMAC-SHA-384 P_SHA-384 TLS_RSA_PSK_WITH_AES_256_CBC_SHA256 HMAC-SHA-256 P_SHA-256 TLS_RSA_PSK_WITH_AES_256_CBC_SHA384 HMAC-SHA-384 P_SHA-384 4. TLS Versions Because these cipher suites depend on features available only in TLS 1.2 (PRF flexibility and combined authenticated encryption cipher modes), they MUST NOT be negotiated by older versions of TLS. Clients MUST NOT offer these cipher suites if they do not offer TLS 1.2 or later. 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. Security Considerations The security considerations in [I-D.ietf-tls-rfc4346-bis], RFC 4279 and RFC 4785 apply to this document as well. The remainder of this section describes security considerations specific to the cipher suites described in this document. 5.1. Counter Reuse with GCM AES-GCM is only secure if the counter is never reused. The IV construction algorithm above is designed to ensure that this cannot happen. 5.2. 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 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 Badra Expires September 29, 2008 [Page 6] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 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 ... 6. IANA Considerations IANA has assigned the following values for the cipher suites defined in this document: CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_258_GCM_SHA256 = {0xXX,0xXX}; Badra Expires September 29, 2008 [Page 7] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA384 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_256_GCM_SHA384 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_128_GCM_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_256_GCM_SHA384 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_128_GCM_SHA256 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_256_GCM_SHA384 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_NULL_SHA256 = {0xXX,0xXX}; CipherSuite TLS_PSK_WITH_NULL_SHA384 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_NULL_SHA256 = {0xXX,0xXX}; CipherSuite TLS_DHE_PSK_WITH_NULL_SHA384 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA384 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA256 = {0xXX,0xXX}; CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA384 = {0xXX,0xXX}; 7. Acknowledgments This draft borrows heavily from [I-D.ietf-tls-ecc-new-mac] and [I- D.ietf-tls-rsa-aes-gcm]. 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. [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- 10, work in progress, March 2008. [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated Encryption", RFC 5116, January 2008. [RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites for Transport Layer Security (TLS)", RFC 4279, December 2005. Badra Expires September 29, 2008 [Page 8] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 [RFC4785] Blumenthal, U., Goel, P., "Pre-Shared Key (PSK) Ciphersuites with NULL Encryption for Transport Layer Security (TLS)", RFC 4785, January 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. [CBC] National Institute of Standards and Technology, "Recommendation for Block Cipher Modes of Operation - Methods and Techniques", SP 800-38A, December 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, November 2007. 8.2. Informative References [Wang05] Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the Full SHA-1", CRYPTO 2005, August 2005. [RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security", RFC 4347, April 2006. [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-04 (work in progress), February 2008. [I-D.ietf-tls-rsa-aes-gcm] Salowey, J., A. Choudhury, and C. McGrew, "RSA based AES- GCM Cipher Suites for TLS", draft-ietf-tls-rsa-aes-gcm-02 (work in progress), February 2008. Author's Addresses Mohamad Badra LIMOS Laboratory - UMR6158, CNRS France Email: badra@isima.fr Badra Expires September 29, 2008 [Page 9] Internet-Draft TLS PSK New MAC and AES-GCM March 2008 Intellectual Property Statement 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. 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Disclaimer of Validity 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. Copyright Statement Copyright (C) The IETF Trust (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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Badra Expires September 29, 2008 [Page 10]