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Versions: 00 01

Network Working Group                                         M. Thomson
Internet-Draft                                                   Mozilla
Updates: I-D.ietf-tls-tls13 (if                             May 24, 2016
         approved)
Intended status: Standards Track
Expires: November 25, 2016


 Cipher Suites for Negotiating Zero Round Trip (0-RTT) Transport Layer
         Security (TLS) with Renewed Certificate Authentication
                  draft-thomson-tls-0rtt-and-certs-01

Abstract

   New cipher suites are defined that allow a client to use zero round
   trip (0-RTT) with Transport Layer Security (TLS), while also enabling
   the peers to renewed certificate-based authentication.

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
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   This Internet-Draft will expire on November 25, 2016.

Copyright Notice

   Copyright (c) 2016 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
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   include Simplified BSD License text as described in Section 4.e of




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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  New Cipher Suites . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Combining Certificate and PSK Authentication  . . . . . . . .   4
   4.  Signaling Support . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Transport Layer Security version 1.3 (TLS 1.3) [I-D.ietf-tls-tls13]
   defines a zero round trip (0-RTT) handshake mode for connections
   where client and server have previously communicated.  In the two
   defined 0-RTT modes, keying material from a previous connection is
   used as a pre-shared key.

   A 0-RTT handshake can rely entirely on the pre-shared key.  These
   handshakes use cipher suites denoted "TLS_PSK_WITH_*".  Alternative
   modes use the pre-shared key to authenticate the connection and
   secure any 0-RTT data, but then a fresh ephemeral Diffie-Hellman (or
   elliptic curve Diffie-Hellman) key exchange is performed.  These
   handshakes use cipher suites denoted "TLS_DHE_PSK_WITH_*" or
   "TLS_ECDHE_PSK_WITH_*".

   Neither of the two 0-RTT handshake modes permits either client or
   server to send the Certificate and CertificateVerify authentication
   messages.  Endpoints are expected to store any authentication state
   with any resumption state.  This means that endpoints are unable to
   update their understanding that a peer has continuing access to
   authentication keys without choosing a one round trip handshake mode
   and sacrificing any potential performance gained by 0-RTT.

   This document defines a third mode for 0-RTT, where the pre-shared
   key is used to authenticate and protect 0-RTT data only.  The
   remainder of the handshake is identical to a regular one round trip
   handshake with the only difference being that the resumption secret
   is mixed into the key schedule.  This allows peers to provide fresh




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   proof that they control authentication keys without losing the
   latency advantages provided by the 0-RTT mode.

1.1.  Notational Conventions

   The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
   document.  It's not shouting; when they are capitalized, they have
   the special meaning defined in [RFC2119].

2.  New Cipher Suites

   The following cipher suites are defined:

   "TLS_ECDHE_PSK_ECDSA_WITH_AES_128_GCM_SHA256 = 0xXXXX
   TLS_ECDHE_PSK_RSA_WITH_AES_128_GCM_SHA256 = 0xXXXX
   TLS_DHE_PSK_RSA_WITH_AES_128_GCM_SHA256 = 0xXXXX
   TLS_ECDHE_PSK_ECDSA_WITH_AES_256_GCM_SHA384 = 0xXXXX
   TLS_ECDHE_PSK_RSA_WITH_AES_256_GCM_SHA384 = 0xXXXX
   TLS_DHE_PSK_RSA_WITH_AES_256_GCM_SHA384 = 0xXXXX
   TLS_ECDHE_PSK_ECDSA_WITH_CHACHA20_POLY1305_SHA256 = 0xXXXX
   TLS_ECDHE_PSK_RSA_WITH_CHACHA20_POLY1305_SHA256 = 0xXXXX
   TLS_DHE_PSK_RSA_WITH_CHACHA20_POLY1305_SHA256 = 0xXXXX "

   All these cipher suites include the use of pre-shared keys and
   therefore permit the use of 0-RTT.  These cipher suites can only be
   used with TLS 1.3.  All include server authentication.  A server MAY
   request client authentication by sending a CertificateRequest if it
   negotiates one of these cipher suites.

   All the necessary cryptographic operations and the key schedule are
   as described in [I-D.ietf-tls-tls13].

   These cipher suites use a pre-shared key for 0-RTT data, with
   subsequent data protected by both the PSK and an ephemeral key
   exchange using finite field or elliptic curve Diffie-Hellman.  The
   pre-shared key forms the static secret (SS) and the ephemeral key
   exchange produces the ephemeral secret (ES).  DHE_PSK_RSA suites use
   finite field Diffie-Hellman key exchange [DH]; ECDHE_PSK_ECDSA and
   ECDHE_PSK_RSA suites use elliptic curve Diffie-Hellman key exchange
   [X962].

   These cipher suites are all authenticated using both the pre-shared
   key and a signature, either from an RSA certificate [RFC3447] (for
   DHE_PSK_RSA and ECDHE_PSK_RSA), or an ECDSA certificate (for
   ECDHE_PSK_ECDSA) [X962].

   AES_128_GCM and AES_256_GCM use the AEAD_AES_128_GCM and
   AEAD_AES_256_GCM authenticated encryption defined in [RFC5116].



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   These are similar to the other AES-GCM modes that are described in
   [RFC5288].  CHACHA20_POLY1305 cipher suites use the authenticated
   encryption defined in [RFC7539].  Other ChaCha20-Poly1305 modes are
   described in [I-D.ietf-tls-chacha20-poly1305].  All authenticated
   encryption modes use the nonce formulation from [I-D.ietf-tls-tls13].

   Suites ending with SHA256 use SHA-256 for the pseudorandom function;
   suites ending with SHA384 use SHA-384 [FIPS180-4].

3.  Combining Certificate and PSK Authentication

   TLS 1.3 forbids a server from selecting different values for many of
   the connection parameters when resuming a connection.  Though a
   client might need to offer a choice in order to support a fallback to
   a 1-RTT handshake, a server cannot change parameters such as the
   selected application layer protocol [RFC7301].  Though it is
   theoretically possible to offer a different certificate with these
   cipher suites, servers MUST NOT change certificates when resuming.
   When resuming, clients MUST treat a change in certificate as a fatal
   error.

   Outside of their use with 0-RTT, these cipher suites also permit the
   use of a combination of pre-shared key and certificate
   authentication.  No real use case for this has been unearthed other
   than with the use of resumption.

   The cached-info extension [I-D.ietf-tls-cached-info] can be used to
   reduce the size of a handshake, allowing more space for application
   data.  Since the server certificate is not permitted to change when
   using 0-RTT with one of these cipher suites, this extension trivially
   saves a considerable amount of space.

4.  Signaling Support

   A TLS server that supports these cipher suites needs to indicate that
   it does so in the NewSessionTicket message.  A new
   "allow_dhe_cert_resumption" value is added to TicketFlags that, when
   set, indicates that the server will accept resumption with cipher
   suites that do both (EC)DHE and certificate authentication.

      enum {
        allow_early_data(1),
        allow_dhe_resumption(2),
        allow_psk_resumption(4),
        allow_dhe_cert_resumption(8) // new
      } TicketFlags;





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   There is no IANA registry for these values, so [I-D.ietf-tls-tls13]
   is updated to include this value.

5.  Security Considerations

   Data sent after the Finished messages in the complete handshake are
   protected based on both the ephemeral key exchange and the pre-shared
   key.  Learning either an (EC)DHE private key or the pre-shared key is
   insufficient to compromise the record protection.

   The combination of pre-shared key and certificate authentication
   relies on peers maintaining the confidentiality of the pre-shared key
   for the confidentiality and integrity of 0-RTT data.

6.  IANA Considerations

   IANA is requested to add the following entries in the TLS Cipher
   Suite Registry:

   "TLS_ECDHE_PSK_ECDSA_WITH_AES_128_GCM_SHA256 = 0xXXXX
   TLS_ECDHE_PSK_RSA_WITH_AES_128_GCM_SHA256 = 0xXXXX
   TLS_DHE_PSK_RSA_WITH_AES_128_GCM_SHA256 = 0xXXXX
   TLS_ECDHE_PSK_ECDSA_WITH_AES_256_GCM_SHA384 = 0xXXXX
   TLS_ECDHE_PSK_RSA_WITH_AES_256_GCM_SHA384 = 0xXXXX
   TLS_DHE_PSK_RSA_WITH_AES_256_GCM_SHA384 = 0xXXXX
   TLS_ECDHE_PSK_ECDSA_WITH_CHACHA20_POLY1305_SHA256 = 0xXXXX
   TLS_ECDHE_PSK_RSA_WITH_CHACHA20_POLY1305_SHA256 = 0xXXXX
   TLS_DHE_PSK_RSA_WITH_CHACHA20_POLY1305_SHA256 = 0xXXXX "

7.  References

7.1.  Normative References

   [DH]       Diffie, W. and M. Hellman, "New Directions in
              Cryptography", IEEE Transactions on Information Theory,
              V.IT-22 n.6 , June 1977.

   [FIPS180-4]
              Department of Commerce, National., "NIST FIPS 180-4,
              Secure Hash Standard", March 2012,
              <http://csrc.nist.gov/publications/fips/fips180-4/
              fips-180-4.pdf>.

   [I-D.ietf-tls-cached-info]
              Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", draft-ietf-tls-
              cached-info-23 (work in progress), May 2016.




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   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-12 (work in progress),
              March 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, DOI 10.17487/RFC3447, February
              2003, <http://www.rfc-editor.org/info/rfc3447>.

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
              <http://www.rfc-editor.org/info/rfc5116>.

   [RFC7539]  Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
              Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
              <http://www.rfc-editor.org/info/rfc7539>.

   [X962]     ANSI, "Public Key Cryptography For The Financial Services
              Industry: The Elliptic Curve Digital Signature Algorithm
              (ECDSA)", ANSI X9.62, 1998.

7.2.  Informative References

   [I-D.ietf-tls-chacha20-poly1305]
              Langley, A., Chang, W., Mavrogiannopoulos, N.,
              Strombergson, J., and S. Josefsson, "ChaCha20-Poly1305
              Cipher Suites for Transport Layer Security (TLS)", draft-
              ietf-tls-chacha20-poly1305-04 (work in progress), December
              2015.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <http://www.rfc-editor.org/info/rfc793>.

   [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,
              <http://www.rfc-editor.org/info/rfc5288>.







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   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
              July 2014, <http://www.rfc-editor.org/info/rfc7301>.

Appendix A.  Acknowledgments

   TBD.

Author's Address

   Martin Thomson
   Mozilla

   Email: martin.thomson@gmail.com




































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