Network Working Group                                        J. Mattsson
Internet-Draft                                                D. Migault
Intended status: Standards Track                                Ericsson
Expires: November 19, 2017                                  May 18, 2017

  ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites for Transport Layer
                             Security (TLS)


   This document defines several new cipher suites for the Transport
   Layer Security (TLS) protocol.  The cipher suites are all based on
   the Ephemeral Elliptic Curve Diffie-Hellman with Pre-Shared Key
   (ECDHE_PSK) key exchange together with the Authenticated Encryption
   with Associated Data (AEAD) algorithms AES-GCM and AES-CCM.  PSK
   provides light and efficient authentication, ECDHE provides forward
   secrecy, and AES-GCM and AES-CCM provides encryption and integrity

Status of This Memo

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   This Internet-Draft will expire on November 19, 2017.

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Requirements notation . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites  . . . . . .   3
   4.  Applicable TLS Versions . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   This document defines new cipher suites that provide Pre-Shared Key
   (PSK) authentication, Perfect Forward Secrecy (PFS), and
   Authenticated Encryption with Associated Data (AEAD).  The cipher
   suites are defined for version 1.2 of the Transport Layer Security
   (TLS) [RFC5246] protocol, version 1.2 of the Datagram Transport Layer
   Security (DTLS) protocol [RFC6347], as well as version 1.3 of TLS

   Pre-Shared Key (PSK) Authentication is widely used in many scenarios.
   One deployment is 3GPP networks where pre-shared keys are used to
   authenticate both subscriber and network.  Another deployment is
   Internet of Things where PSK authentication is often preferred for
   performance and energy efficiency reasons.  In both scenarios the
   endpoints are owned/controlled by a party that provisions the pre-
   shared keys and makes sure that they provide a high level of entropy.

   Perfect Forward Secrecy (PFS) is a strongly recommended feature in
   security protocol design and can be accomplished by using an
   ephemeral Diffie-Hellman key exchange method.  Ephemeral Elliptic
   Curve Diffie-Hellman (ECDHE) provides PFS with excellent performance

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   and small key sizes.  ECDHE is mandatory to implement in both HTTP/2
   [RFC7540] and CoAP [RFC7252].

   AEAD algorithms that combine encryption and integrity protection are
   strongly recommended for (D)TLS [RFC7525] and non-AEAD algorithms are
   forbidden to use in TLS 1.3 [I-D.ietf-tls-tls13].  The AEAD
   algorithms considered in this document are AES-GCM and AES-CCM.  The
   use of AES-GCM in TLS is defined in [RFC5288] and the use of AES-CCM
   is defined in [RFC6655].

   [RFC4279] defines Pre-Shared Key (PSK) cipher suites for TLS but does
   not consider Elliptic Curve Cryptography.  [RFC4492] introduces
   Elliptic Curve Cryptography for TLS but does not consider PSK
   authentication.  [RFC5487] describes the use of AES-GCM in
   combination with PSK authentication, but does not consider ECDHE.
   [RFC5489] describes the use of PSK in combination with ECDHE but does
   not consider AES-GCM or AES-CCM.

3.  ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites

   The cipher suites defined in this document are based on the AES-GCM
   and AES-CCM Authenticated Encryption with Associated Data (AEAD)
   algorithms AEAD_AES_128_GCM, AEAD_AES_256_GCM and AEAD_AES_128_CCM
   defined in [RFC5116], and AEAD_AES_128_CCM_8 defined in [RFC6655].

   Messages and pre-master secret construction in this document are
   defined in [RFC5489].  The ServerKeyExchange and ClientKeyExchange
   messages are used and the pre-master secret is computed as for the
   ECDHE_PSK key exchange.  The elliptic curve parameters used in in the
   Diffie-Hellman parameters are negotiated using extensions defined in

   For TLS 1.2, the following cipher suites are defined:


   The assigned code points can only be used for TLS 1.2.

4.  Applicable TLS Versions

   The cipher suites defined in this document MUST NOT be negotiated for
   any version of (D)TLS other than TLS 1.2.

   TLS version 1.3 and later negotiate these features in a different
   manner.  Unlike TLS 1.2, TLS 1.3 separates authentication and cipher

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   suite negotiation [I-D.ietf-tls-tls13] Section 1.2.  TLS 1.3 supports
   PSK with ECDHE key exchange and the cipher suites
   TLS_AES_128_GCM_SHA256, TLS_AES_256_GCM_SHA384,
   TLS_AES_128_CCM_8_SHA256 and TLS_AES_128_CCM_SHA256 are part of the
   specification.  As a result, TLS 1.3 and higher versions, negotiate
   and support these cipher suites in a different way.

   The cipher suites defined in this document make use of the
   authenticated encryption with additional data (AEAD) defined in TLS
   1.2 [RFC5246] and DTLS 1.2 [RFC6347].  Earlier versions of TLS do not
   have support for AEAD and consequently, the cipher suites defined in
   this document MUST NOT be negotiated in TLS versions prior to 1.2.
   In addition, it is worth noting that TLS 1.0 [RFC2246] and TL1.2
   [RFC4346] splits the pre-master in two parts.  The PRF results from
   mixing the two pseudorandom streams with distinct hash functions (MD5
   and SHA-1) by exclusive-ORing them together.  In the case of
   ECDHE_PSK authentication, the PSK and pre-master are treated by
   distinct hash function with distinct properties.  This may introduce
   vulnerabilities over the expected security provided by the
   constructed pre-master.  As such TLS 1.0 and TLS 1.1 should not be
   used with ECDHE_PSK.

   A client that offers the cipher suites from this document in
   ClientHello.cipher_suites in combination with (3,1) "TLS 1.0" or
   (3,2) "TLS 1.1" in ClientHello.client_version MUST support TLS 1.2
   and MUST accept the server to negotiate TLS 1.2 for the current
   session.  If the client does not support TLS 1.2 or is not willing to
   negotiate TLS 1.2, then this client MUST NOT offer any of these
   cipher suites with a lower protocol version than (3,3) "TLS 1.2" in

   A server receiving a ClientHello and a client_version indicating
   (3,1) "TLS 1.0" or (3,2) "TLS 1.1" and any of the cipher suites from
   this document in ClientHello.cipher_suites can safely assume that the
   client supports TLS 1.2 and is willing to use it.  The server MUST
   NOT negotiate these cipher suites with TLS protocol versions earlier
   than TLS 1.2.  Not requiring clients to indicate their support for
   TLS 1.2 cipher suites exclusively through ClientHello.client_hello
   improves the interoperability in the installed base and use of TLS
   1.2 AEAD cipher suites without upsetting the installed base of
   version-intolerant TLS servers, results in more TLS handshakes
   succeeding and obviates fallback mechanisms.

5.  IANA Considerations

   This document defines the following new cipher suites, whose values
   have been assigned in the TLS Cipher Suite Registry defined by

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   TLS_ECDHE_PSK_WITH_AES_128_GCM_SHA256   = {0xTBD; 0xTBD} {0xD0,0x01};
   TLS_ECDHE_PSK_WITH_AES_256_GCM_SHA384   = {0xTBD; 0xTBD} {0xD0,0x02};
   TLS_ECDHE_PSK_WITH_AES_128_CCM_8_SHA256 = {0xTBD; 0xTBD} {0xD0,0x03};
   TLS_ECDHE_PSK_WITH_AES_128_CCM_SHA256   = {0xTBD; 0xTBD} {0xD0,0x05};

   suite numbers listed in the last column are numbers used for cipher
   suite interoperability testing and it's suggested that IANA use these
   values for assignment.

6.  Security Considerations

   The security considerations in TLS 1.2 [RFC5246], DTLS 1.2 [RFC6347],
   TLS 1.3 [I-D.ietf-tls-tls13], ECDHE_PSK [RFC5489], AES-GCM [RFC5288],
   and AES-CCM [RFC6655] apply to this document as well.

   All the cipher suites defined in this document provide
   confidentiality, mutual authentication, and forward secrecy.  The
   AES-128 cipher suites provide 128-bit security and the AES-256 cipher
   suites provide at least 192-bit security.  However, AES_128_CCM_8
   only provides 64-bit security against message forgery.

   Use of Pre-Shared Keys of limited entropy may allow an active
   attacker attempts to connect to the server and try different keys.
   For example, limited entropy may be provided by using a short PSK in
   which case an attacker may perform a brute-force attack.  Another
   example includes the use of a PSK chosen by a human which thus may be
   exposed to dictionary attacks.

   The Pre-Shared Keys used for authentication MUST have a security
   level equal or higher than the cipher suite used, i.e., at least
   128-bit for the AES-128 cipher suites and at least 192-bit for the
   AES-256 cipher suites.

   GCM or CCM encryption - even of different clear text - re-using a
   nonce with a same key undermines the security of GCM and CCM.  As a
   result, GCM and CCM MUST only be used with a system guaranteeing
   nonce uniqueness [RFC5116].

7.  Acknowledgements

   The authors would like to thank Ilari Liusvaara, Eric Rescorla, Dan
   Harkins, Russ Housley, Dan Harkins, Martin Thomson, Nikos
   Mavrogiannopoulos, Peter Dettman, Xiaoyin Liu, Joseph Salowey, Sean
   Turner Dave Garrett, Martin Rex and Kathleen Moriarty for their
   valuable comments and feedback.

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8.  References

8.1.  Normative References

              Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
              Curve Cryptography (ECC) Cipher Suites for Transport Layer
              Security (TLS) Versions 1.2 and Earlier", draft-ietf-tls-
              rfc4492bis-17 (work in progress), May 2017.

              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-20 (work in progress),
              April 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, DOI 10.17487/RFC2246, January 1999,

   [RFC4279]  Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 4279, DOI 10.17487/RFC4279, December 2005,

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346,
              DOI 10.17487/RFC4346, April 2006,

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,

   [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
              Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
              DOI 10.17487/RFC5288, August 2008,

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   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <>.

   [RFC6655]  McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
              Transport Layer Security (TLS)", RFC 6655,
              DOI 10.17487/RFC6655, July 2012,

8.2.  Informative References

   [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,
              DOI 10.17487/RFC4492, May 2006,

   [RFC5487]  Badra, M., "Pre-Shared Key Cipher Suites for TLS with SHA-
              256/384 and AES Galois Counter Mode", RFC 5487,
              DOI 10.17487/RFC5487, March 2009,

   [RFC5489]  Badra, M. and I. Hajjeh, "ECDHE_PSK Cipher Suites for
              Transport Layer Security (TLS)", RFC 5489,
              DOI 10.17487/RFC5489, March 2009,

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,

Authors' Addresses

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   John Mattsson
   Ericsson AB
   SE-164 80 Stockholm

   Phone: +46 76 115 35 01

   Daniel Migault
   8400 boulevard Decarie
   Montreal, QC   H4P 2N2

   Phone: +1 514-452-2160

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