Network Working Group                                        J. Mattsson
Internet-Draft                                                D. Migault
Intended status: Standards Track                                Ericsson
Expires: May 17, 2017                                  November 13, 2016

            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 perfect
   forward secrecy, and AES-GCM and AES-CCM provides encryption and
   integrity protection.

Status of This Memo

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   This Internet-Draft will expire on May 17, 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 . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

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 or later of the Transport Layer
   Security (TLS) [RFC5246] protocol, as well as version 1.2 or later of
   the Datagram Transport Layer Security (DTLS) protocol [RFC6347].

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

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   AEAD algorithms that combine encryption and integrity protection are
   strongly recommended [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, AEAD_AES_128_CCM, and
   AEAD_AES_256_CCM defined in [RFC5116], AEAD_AES_128_CCM_8 and
   AEAD_AES_256_CCM_8 defined in [RFC6655].

   For TLS1.2, the following cipher suites are defined:


   The assigned code points are only expected to be used for TLS 1.2.
   TLS 1.3 does not follow the same name convention.  Instead TLS 1.3
   cipher suites are designated according to the AEAD suite as well as
   the hash function used.  The current combination of AEAD algorithms
   and Hash fucntion are already defined in TLS 1.3 so there is no need
   to add additional cipher suites for TLS 1.3.

   Instead, in order to used the ECDHE_PSK authentication method, TLS
   1.3 uses a combination of the "key_share" and
   "psk_key_exchange_modes" extentions. "psk_key_exchange_modes"
   extension sets its mode to psk_dhe_ke.  The "key_share" extention
   contains a KeyShareEntry structure that carries the ECDHE parameters.

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4.  Applicable TLS Versions

   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, these cipher suites MUST NOT
   be negotiated in TLS versions prior to 1.2.  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.  A client MUST treat the selection of these cipher
   suites in combination with a version of TLS that does not support
   AEAD (i.e., TLS 1.1 or earlier) as an error and generate a fatal
   'illegal_parameter' TLS alert.

5.  IANA Considerations

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

   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_256_CCM_8_SHA256 = {0xTBD; 0xTBD} {0xD0,0x04};
   TLS_ECDHE_PSK_WITH_AES_128_CCM_SHA256   = {0xTBD; 0xTBD} {0xD0,0x05};
   TLS_ECDHE_PSK_WITH_AES_256_CCM_SHA384   = {0xTBD; 0xTBD} {0xD0,0x06};

   The cipher suite numbers listed in the second 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 perfect 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
   and AES_256_GCM and AES_256_CCM only provide 128-bit security against
   message forgery.

   Use of Pre-Shared Keys of limited entropy (for example, a PSK that is
   relatively short, or was chosen by a human and thus may contain less
   entropy than its length would imply) may allow an active attacker to

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   perform a brute-force attack where the attacker attempts to connect
   to the server and tries different keys.  Passive eavesdropping alone
   is not sufficient.  For these reasons 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.

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 and Sean Turner for
   their valuable comments and feedback.

8.  References

8.1.  Normative References

              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-18 (work in progress),
              October 2016.

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

   [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,

   [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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