Network Working Group M. Salter Internet-Draft National Security Agency Intended status: Informational E. Rescorla Expires: March 9, 2009 Network Resonance R. Housley Vigil Security September 5, 2008 Suite B Cipher Suites for TLS draft-rescorla-tls-suiteb-03.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 March 9, 2009. Abstract The United States Government has published guidelines for "NSA Suite B Cryptography," which defines cryptographic algorithm polcy for national security applications. This document defines a profile of TLS which is conformant with Suite B. Salter, et al. Expires March 9, 2009 [Page 1] Internet-Draft Suite B for TLS September 2008 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 . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Acceptable Curves . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Salter, et al. Expires March 9, 2009 [Page 2] Internet-Draft Suite B for TLS September 2008 1. Introduction National Security Agency posted a Fact Sheet on Suite B Cryptography, and it states: 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. 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 Fact Sheet on Suite B Cryptography 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, Suite B includes: Salter, et al. Expires March 9, 2009 [Page 3] Internet-Draft Suite B for TLS September 2008 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 - 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) 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. Note: Some people refer to the two security levels based on the AES key size that is employed. At the 128-bit security level, an AES key length of 128 bits is used. However, at the 192-bit security level, an AES key length of 256 bits is used. 4. Suite B Compliance Requirements Galois Counter Mode (GCM) cipher suites [I-D.ietf-tls-ecc-new-mac] are preferred for Suite B implementations. However, TLS 1.1 (or earlier) does not support GCM. Therefore, when TLS 1.1 (or earlier) implementations are used in Suite B mode, they support Cipher Block Chaining (CBC) mode. Therefore, in order for a connection to be Suite B compliant, the following rules apply: o TLS 1.1 or earlier connections MUST use either TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA or TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA. A compliant TLS 1.1 or earlier client MUST offer at least one of these cipher suites. A compliant TLS 1.1 or earlier server MUST select one of them if offered. o TLS 1.2 or greater connections connections MUST use one of TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256, TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384, TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, or TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384. A compliant TLS 1.2 or Salter, et al. Expires March 9, 2009 [Page 4] Internet-Draft Suite B for TLS September 2008 greater client MUST offer one or both of the two GCM cipher suites. If backward compatibility with TLS 1.1 or earlier is desired, it MAY offer one or both of the CBC cipher suites as well. A compliant TLS 1.2 server MUST select one of these cipher suites if offered and MUST select a GCM cipher suite in TLS 1.2 mode if one is offered. Note that these rules explicitly permit the use of CBC cipher suites in TLS 1.2 connections in order to permit operation between Suite B and non-Suite B implementations. For instance, a Suite B compliant TLS 1.2 client might offer TLS 1.2 with both CBC and GCM cipher suites when communicating with a non-Suite B TLS 1.2 server which then selected the CBC cipher suites. This connection would nevertheless meet the requirements of this specification. However, any two Suite B implementations will negotiate a GCM cipher suite when doing TLS 1.2. 4.1. Security Levels As described in Section 1, Suite B specifies two security levels: 128 bit and 192 bit. The following table lists the security levels for each cipher suite: +-----------------------------------------+----------------+ | Cipher Suite | Security Level | +-----------------------------------------+----------------+ | TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA | 128 | | TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 | 128 | | TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA | 192 | | TLS_ECDHE_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 [DSS] 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 also 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 Salter, et al. Expires March 9, 2009 [Page 5] Internet-Draft Suite B for TLS September 2008 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], [I-D.ietf-tls-rsa-aes-gcm], 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 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. Salter, et al. Expires March 9, 2009 [Page 6] Internet-Draft Suite B for TLS September 2008 [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. [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-07 (work in progress), May 2008. [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. [DSS] National Institute of Standards and Technology, "Digital Signature Standard", FIPS 186-2, January 2000. 8.2. Informative References [I-D.ietf-tls-rsa-aes-gcm] Salowey, J., Choudhury, A., and D. McGrew, "AES-GCM Cipher Suites for TLS", draft-ietf-tls-rsa-aes-gcm-03 (work in progress), April 2008. Authors' Addresses Margaret Salter National Security Agency 9800 Savage Rd. Fort Meade 20755-6709 USA Email: msalter@restarea.ncsc.mil Eric Rescorla Network Resonance 2064 Edgewood Drive Palo Alto 94303 USA Email: ekr@rtfm.com Salter, et al. Expires March 9, 2009 [Page 7] Internet-Draft Suite B for TLS September 2008 Russ Housley Vigil Security 918 Spring Knoll Drive Herndon 21070 USA Email: housley@vigilsec.com Salter, et al. Expires March 9, 2009 [Page 8] Internet-Draft Suite B for TLS September 2008 Full 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. 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. 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