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TLS Working Group                                              D. McGrew
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                               D. Bailey
Expires: July 23, 2011                                           RSA/EMC
                                                             M. Campagna
                                                                R. Dugal
                                                          Certicom Corp.
                                                        January 19, 2011


                   AES-CCM ECC Cipher Suites for TLS
                    draft-mcgrew-tls-aes-ccm-ecc-01

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) to provide confidentiality and data origin
   authentication.  The AES-CCM algorithm is amenable to compact
   implementations, making it suitable for constrained environments.
   The ciphersuites defined in this document use Elliptic Curve
   Cryptography (ECC), and are intended for use in networks with limited
   bandwidth.

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 July 23, 2011.

Copyright Notice

   Copyright (c) 2011 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



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   (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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions Used In This Document  . . . . . . . . . . . .  3

   2.  ECC based AES-CCM Cipher Suites  . . . . . . . . . . . . . . .  4
     2.1.  Required Algorithms for each CipherSuite . . . . . . . . .  5

   3.  TLS Versions . . . . . . . . . . . . . . . . . . . . . . . . .  7

   4.  New AEAD algorithms  . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  AES-128-CCM with an 8-octet ICV  . . . . . . . . . . . . .  8
     4.2.  AES-256-CCM with an 8-octet ICV  . . . . . . . . . . . . .  8

   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9

   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
     6.1.  Perfect Forward Secrecy  . . . . . . . . . . . . . . . . . 10
     6.2.  Counter Reuse  . . . . . . . . . . . . . . . . . . . . . . 10

   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11

   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 13

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14















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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 in this note; these use AES-CCM but 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 Ephemeral Elliptic
   Curve Diffie-Hellman (ECDHE) as their key establishment mechanism;
   these ciphersuites can be used with DTLS [I-D.ietf-tls-rfc4347-bis].

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]



















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2.  ECC based AES-CCM Cipher Suites

   The ciphersuites defined in this document are based on the AES-CCM
   authenticated encryption with associated data (AEAD) algorithms
   AEAD_AES_128_CCM and AEAD_AES_256_CCM described in [RFC5116].  The
   following ciphersuites are defined:

      CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM = {TBD1,TBD1}
      CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CCM = {TBD2,TBD2)
      CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 = {TBD3,TBD3}
      CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8 = {TBD4,TBD4)

   These ciphersuites make use of the AEAD capability in TLS 1.2
   [RFC5246].  Note that each of these AEAD algorithms uses AES-CCM.
   Ciphersuites ending with "8" use eight-octet authentication tags; the
   other ciphersuites have 16 octet authentication tags.

   The HMAC truncation option described in Section 3.5 of [RFC4366]
   (which negotiates the "truncated_hmac" TLS extension) does not have
   an effect on the cipher suites defined in this note, because they do
   not use HMAC to protect TLS records.

   The "nonce" input to the AEAD algorithm is defined as in [RFC5288].
   The "nonce" SHALL be 12 bytes long and 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 field is the 16-bit DTLS epoch field
   concatenated with the 48-bit sequence_number field.  The epoch and
   sequence_number appear in the DTLS record layer.

   This construction allows the internal counter to be 32-bits long,
   which is a convenient size for use with CCM.

   These ciphersuites make use of the default TLS 1.2 Pseudorandom
   Function (PRF), which uses HMAC with the SHA-256 hash function.

   The ECDHE_ECDSA key exchange is performed as defined in [RFC4492],
   with the following additional stipulations:

      The curves secp256r1 and secp384r1 MUST be supported, and the
      curve secp521r1 MAY be supported; these curves are equivalent to



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      the NIST P-256, P-384, and P-521 curves.  Note that all of these
      curves have cofactor equal to one, which simplifies their use.

      The server's certificate MUST contain an ECDSA-capable public key,
      it MUST be signed with ECDSA, and it MUST use SHA-256, SHA-384, or
      SHA-512.  The Signature Algorithms extension (Section 7.4.1.4.1 of
      [RFC5246]) MUST be used to indicate support of those signature and
      hash algorithms.  If a client certificate is used, the same
      conditions apply to it.  The acceptable choices of hashes and
      curves that can be used with each ciphersuite are detailed in
      Section 2.1.

      The uncompressed point format MUST be supported.  Other point
      formats MAY be used.

      The client MUST offer the elliptic_curves extension and the server
      MUST expect to receive it.

      The client MAY offer the ec_point_formats extension, but the
      server need not expect to receive it.

      [I-D.mcgrew-fundamental-ecc] MAY be used as an implementation
      method.

   Implementations of these ciphersuites will interoperate with
   [RFC4492], but can be more compact than a full implementation of that
   RFC.

2.1.  Required Algorithms for each CipherSuite

   The curves and hash algorithms that can be used with each ciphersuite
   are described in the following table.

   +--------------------------------------------+----------------------+
   | CipherSuite                                | Algorithms           |
   +--------------------------------------------+----------------------+
   | TLS_ECDHE_ECDSA_WITH_AES_128_CCM           | MUST support         |
   | TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8         | secp256r1, SHA-256   |
   |                                            |                      |
   |                                            | MAY support          |
   |                                            | secp384r1, SHA-384   |
   |                                            |                      |
   |                                            | MAY support          |
   |                                            | secp521r1, SHA-512   |
   |                                            |                      |
   | TLS_ECDHE_ECDSA_WITH_AES_256_CCM           | MUST support         |
   | TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8         | secp384r1, SHA-384   |
   |                                            |                      |



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   |                                            | MAY support          |
   |                                            | secp521r1, SHA-512   |
   +--------------------------------------------+----------------------+
















































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3.  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.






































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4.  New AEAD algorithms

   The following AEAD algorithms are defined:

      AEAD_AES_128_CCM_8 = TBD9
      AEAD_AES_256_CCM_8 = TBD10
      AEAD_AES_128_CCM_12 = TBD11
      AEAD_AES_256_CCM_12 = TBD12

4.1.  AES-128-CCM with an 8-octet 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.

4.2.  AES-256-CCM with an 8-octet 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 for
   AEAD_AES_128_CCM.  An AEAD_AES_128_CCM_8 ciphertext is exactly 8
   octets longer than its corresponding plaintext.

















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5.  IANA Considerations

   IANA has assigned values for the Ciphersuites defined in Section 2
   and the AEAD algorithms defined in Section 4 of this note.















































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6.  Security Considerations

6.1.  Perfect Forward Secrecy

   The perfect forward secrecy properties of ephemeral Diffie-Hellman
   ciphersuites are discussed in the security analysis of [RFC4346].
   This analysis applies to the ECDHE ciphersuites.

6.2.  Counter Reuse

   AES-CCM security requires that the counter is never reused.  The IV
   construction in Section 2 is designed to prevent counter reuse.







































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7.  Acknowledgements

   This draft borrows heavily from [RFC5288].

   This draft is motivated by the considerations raised in the Zigbee
   Smart Energy 2.0 working group.













































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8.  References

8.1.  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.

   [I-D.ietf-tls-rfc4347-bis]
              Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security version 1.2", draft-ietf-tls-rfc4347-bis-03 (work
              in progress), October 2009.

   [I-D.mcgrew-fundamental-ecc]
              McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
              Curve Cryptography Algorithms",
              draft-mcgrew-fundamental-ecc-04 (work in progress),
              December 2010.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, April 2006.

   [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.

   [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.




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8.2.  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.









































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Authors' Addresses

   David McGrew
   Cisco Systems, Inc.
   170 W Tasman Drive
   San Jose, CA  95134
   USA

   Email: mcgrew@cisco.com


   Daniel V. Bailey
   RSA/EMC
   174 Middlesex Tpke.
   Bedford, MA  01463
   USA

   Email: dbailey@rsa.com


   Matthew Campagna
   Certicom Corp.
   5520 Explorer Drive #400
   Mississauga, Ontario  L4W 5L1
   Canada

   Email: mcampagna@certicom.com


   Robert Dugal
   Certicom Corp.
   5520 Explorer Drive #400
   Mississauga, Ontario  L4W 5L1
   Canada

   Email: rdugal@certicom.com















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