TLS Working Group D. McGrew Internet-Draft Cisco Systems Intended status: Standards Track D. Bailey Expires: August 16, 2012 RSA, the Security Division of EMC February 13, 2012 AES-CCM Cipher Suites for TLS draft-mcgrew-tls-aes-ccm-03 Abstract This memo describes the use of the Advanced Encryption Standard (AES) in the Counter and CBC-MAC Mode (CCM) of operation within Transport Layer Security (TLS) and Datagram TLS (DTLS) to provide confidentiality and data origin authentication. The AES-CCM algorithm is amenable to compact implementations, making it suitable for constrained environments. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on August 16, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of McGrew & Bailey Expires August 16, 2012 [Page 1] Internet-Draft AES-CCM Ciphersuites February 2012 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used In This Document . . . . . . . . . . . . . . . 3 3. RSA Based AES-CCM Cipher Suites . . . . . . . . . . . . . . . . 3 4. PSK Based AES-CCM Cipher Suites . . . . . . . . . . . . . . . . 4 5. TLS Versions . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. New AEAD algorithms . . . . . . . . . . . . . . . . . . . . . . 5 6.1. AES-128-CCM with an 8-octet Integrity Check Value (ICV) . . 5 6.2. AES-256-CCM with a 8-octet Integrity Check Value (ICV) . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 8.1. Perfect Forward Secrecy . . . . . . . . . . . . . . . . . . 6 8.2. Counter Reuse . . . . . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 10.1. Normative References . . . . . . . . . . . . . . . . . . . 7 10.2. Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 McGrew & Bailey Expires August 16, 2012 [Page 2] Internet-Draft AES-CCM Ciphersuites February 2012 1. Introduction This document describes the use of Advanced Encryption Standard (AES) [AES] in Counter with CBC-MAC Mode (CCM) [CCM] in several TLS ciphersuites. AES-CCM provides both authentication and confidentiality and uses as its only primitive the AES encrypt operation (the AES decrypt operation is not needed). This makes it amenable to compact implementations, which is advantageous in constrained environments. The use of AES-CCM has been specified for IPsec ESP [RFC4309] and 802.15.4 wireless networks [IEEE802154]. Authenticated encryption, in addition to providing confidentiality for the plaintext that is encrypted, provides a way to check its integrity and authenticity. Authenticated Encryption with Associated Data, or AEAD [RFC5116], adds the ability to check the integrity and authenticity of some associated data that is not encrypted. This note utilizes the AEAD facility within TLS 1.2 [RFC5246] and the AES- CCM-based AEAD algorithms defined in [RFC5116]. Additional AEAD algorithms are defined, which use AES-CCM but which have shorter authentication tags, and therefore are more suitable for use across networks in which bandwidth is constrained and message sizes may be small. The ciphersuites defined in this document use RSA or Pre-Shared Key (PSK) as their key establishment mechanism; these ciphersuites can be used with DTLS [RFC6347]. Since the abiltiy to use AEAD ciphers was introduced in DTLS version 1.2, the ciphersuites defined in this note cannot be used with earlier versions of that protocol. 2. Conventions Used In This Document he 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. RSA Based AES-CCM Cipher Suites The ciphersuites defined in this document are based on the the AES- CCM authenticated encryption with associated data (AEAD) algorithms AEAD_AES_128_CCM and AEAD_AES_256_CCM described in [RFC5116]. The following RSA-based ciphersuites are defined: McGrew & Bailey Expires August 16, 2012 [Page 3] Internet-Draft AES-CCM Ciphersuites February 2012 CipherSuite TLS_RSA_WITH_AES_128_CCM = {TBD1,TBD1} CipherSuite TLS_RSA_WITH_AES_256_CCM = {TBD2,TBD2) CipherSuite TLS_RSA_DHE_WITH_AES_128_CCM = {TBD3,TBD3} CipherSuite TLS_RSA_DHE_WITH_AES_256_CCM = {TBD4,TBD4} CipherSuite TLS_RSA_WITH_AES_128_CCM_8 = {TBD5,TBD5} CipherSuite TLS_RSA_WITH_AES_256_CCM_8 = {TBD6,TBD6) CipherSuite TLS_RSA_DHE_WITH_AES_128_CCM_8 = {TBD7,TBD7} CipherSuite TLS_RSA_DHE_WITH_AES_256_CCM_8 = {TBD8,TBD8} These ciphersuites make use of the AEAD capability in TLS 1.2 [RFC5246]. Each uses AES-CCM; those that end in "_8" have an 8-octet authentication tag, while the other ciphersuites have 16-octet authentication tags. The HMAC truncation option described in Section 7 of [RFC6066] (which negotiates the "truncated_hmac" TLS extension) does not have an effect on cipher suites that do not use HMAC. The "nonce" input to the AEAD algorithm is exactly that of [RFC5288]: the "nonce" SHALL be 12 bytes long and is constructed as follows: struct { case client: uint32 client_write_IV; // low order 32-bits case server: uint32 server_write_IV; // low order 32-bits uint64 seq_num; } CCMNonce. In DTLS, the 64-bit seq_num is the 16-bit epoch concatenated with the 48-bit seq_num. These ciphersuites make use of the default TLS 1.2 Pseudorandom Function (PRF), which uses HMAC with the SHA-256 hash function. The RSA and RSA-DHE key exchange is performed as defined in [RFC5288]. 4. PSK Based AES-CCM Cipher Suites As in Section Section 3, these ciphersuites follow [RFC5116]. The following ciphersuites are defined: CipherSuite TLS_PSK_WITH_AES_128_CCM = {TBD9,TBD9} CipherSuite TLS_PSK_WITH_AES_256_CCM = {TBD10,TBD10) CipherSuite TLS_PSK_DHE_WITH_AES_128_CCM = {TBD11,TBD11} CipherSuite TLS_PSK_DHE_WITH_AES_256_CCM = {TBD12,TBD12} CipherSuite TLS_PSK_WITH_AES_128_CCM_8 = {TBD13,TBD13} CipherSuite TLS_PSK_WITH_AES_256_CCM_8 = {TBD14,TBD14) McGrew & Bailey Expires August 16, 2012 [Page 4] Internet-Draft AES-CCM Ciphersuites February 2012 CipherSuite TLS_PSK_DHE_WITH_AES_128_CCM_8 = {TBD15,TBD15} CipherSuite TLS_PSK_DHE_WITH_AES_256_CCM_8 = {TBD16,TBD16} The "nonce" input to the AEAD algorithm is defined as in Section Section 3. These ciphersuites make use of the default TLS 1.2 Pseudorandom Function (PRF), which uses HMAC with the SHA-256 hash function. The PSK and PSK-DHE key exchange is performed as defined in [RFC5487]. 5. TLS Versions These ciphersuites make use of the authenticated encryption with additional data defined in TLS 1.2 [RFC5288]. 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 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. 6. New AEAD algorithms The following AEAD algorithms are defined: AEAD_AES_128_CCM_8 = TBD17 AEAD_AES_256_CCM_8 = TBD18 6.1. AES-128-CCM with an 8-octet Integrity Check Value (ICV) The AEAD_AES_128_CCM_8 authenticated encryption algorithm is identical to the AEAD_AES_128_CCM algorithm (see Section 5.3 of [RFC5116]), except that it uses eight octets for authentication, instead of the full sixteen octets used by AEAD_AES_128_CCM. The AEAD_AES_128_CCM_8 ciphertext consists of the ciphertext output of the CCM encryption operation concatenated with the 8-octet authentication tag output of the CCM encryption operation. Test cases are provided in [CCM]. The input and output lengths are as for AEAD_AES_128_CCM. An AEAD_AES_128_CCM_8 ciphertext is exactly 8 octets longer than its corresponding plaintext. McGrew & Bailey Expires August 16, 2012 [Page 5] Internet-Draft AES-CCM Ciphersuites February 2012 6.2. AES-256-CCM with a 8-octet Integrity Check Value (ICV) The AEAD_AES_256_CCM_8 authenticated encryption algorithm is identical to the AEAD_AES_256_CCM algorithm (see Section 5.4 of [RFC5116]), except that it uses eight octets for authentication, instead of the full sixteen octets used by AEAD_AES_256_CCM. The AEAD_AES_256_CCM_8 ciphertext consists of the ciphertext output of the CCM encryption operation concatenated with the 8-octet authentication tag output of the CCM encryption operation. Test cases are provided in [CCM]. The input and output lengths are as as for AEAD_AES_128_CCM. An AEAD_AES_128_CCM_8 ciphertext is exactly 8 octets longer than its corresponding plaintext. 7. IANA Considerations IANA is requested to assign the values for the ciphersuites defined in Section 3 and Section 4 from the TLS and DTLS CipherSuite registries, and the values of the AEAD algorithms defined in Section 6 from the AEAD algorithm registry. IANA, please note that the DTLS-OK column should be marked as "Y" for each of these algorithms. 8. Security Considerations 8.1. Perfect Forward Secrecy The perfect forward secrecy properties of RSA based TLS ciphersuites are discussed in the security analysis of [RFC5246]. It should be noted that only the ephemeral Diffie-Hellman based ciphersuites are capable of providing perfect forward secrecy. 8.2. Counter Reuse AES-CCM security requires that the counter is never reused. The IV construction in Section 3 is designed to prevent counter reuse. 9. Acknowledgements This draft borrows heavily from [RFC5288]. 10. References McGrew & Bailey Expires August 16, 2012 [Page 6] Internet-Draft AES-CCM Ciphersuites February 2012 10.1. Normative References [AES] National Institute of Standards and Technology, "Specification for the Advanced Encryption Standard (AES)", FIPS 197, November 2001. [CCM] National Institute of Standards and Technology, "Recommendation for Block Cipher Modes of Operation: The CCM Mode for Authentication and Confidentiality", SP 800- 38C, May 2004. [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. [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, August 2008. [RFC5487] Badra, M., "Pre-Shared Key Cipher Suites for TLS with SHA- 256/384 and AES Galois Counter Mode", RFC 5487, March 2009. [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, January 2011. [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, January 2012. 10.2. Informative References [IEEE802154] Institute of Electrical and Electronics Engineers, "Wireless Personal Area Networks", IEEE Standard 802.15.4- 2006, 2006. [RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM Mode with IPsec Encapsulating Security Payload (ESP)", RFC 4309, December 2005. McGrew & Bailey Expires August 16, 2012 [Page 7] Internet-Draft AES-CCM Ciphersuites February 2012 Authors' Addresses David McGrew Cisco Systems 13600 Dulles Technology Drive Herndon, VA 20171 USA Email: mcgrew@cisco.com Daniel V. Bailey RSA, the Security Division of EMC 174 Middlesex Tpke. Bedford, MA 01463 USA Email: dbailey@rsa.com McGrew & Bailey Expires August 16, 2012 [Page 8]