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Versions: 00 01 02 03 04 05 draft-ietf-tls-chacha20-poly1305

Network Working Group                                         A. Langley
Internet-Draft                                                  W. Chang
Updates: 5246, 6347 (if approved)                             Google Inc
Intended status: Standards Track                    N. Mavrogiannopoulos
Expires: October 5, 2015                                         Red Hat
                                                         J. Strombergson
                                                      Secworks Sweden AB
                                                            S. Josefsson
                                                                  SJD AB
                                                           April 3, 2015


         The ChaCha Stream Cipher for Transport Layer Security
                 draft-mavrogiannopoulos-chacha-tls-05

Abstract

   This document describes the use of the ChaCha stream cipher with
   Poly1305 in Transport Layer Security (TLS) and Datagram Transport
   Layer Security (DTLS) protocols.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 5, 2015.

Copyright Notice

   Copyright (c) 2015 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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   carefully, as they describe your rights and restrictions with respect



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The ChaCha Cipher . . . . . . . . . . . . . . . . . . . . . .   3
   3.  The Poly1305 Authenticator  . . . . . . . . . . . . . . . . .   3
   4.  ChaCha20 Cipher Suites  . . . . . . . . . . . . . . . . . . .   3
     4.1.  ChaCha20 Cipher Suites with Poly1305  . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This document describes the use of the ChaCha stream cipher in the
   Transport Layer Security (TLS) version 1.2 [RFC5246] protocol, as
   well as in the Datagram Transport Layer Security (DTLS) version 1.2
   [RFC6347], or any later versions.

   ChaCha [CHACHA] is a stream cipher that has been designed for high
   performance in software implementations.  The cipher has compact
   implementation and uses few resources and inexpensive operations that
   makes it suitable for implementation on a wide range of
   architectures.  It has been designed to prevent leakage of
   information through side channel analysis, has a simple and fast key
   setup and provides good overall performance.  It is a variant of
   Salsa20 [SALSA20SPEC] which is one of the selected ciphers in the
   eSTREAM portfolio [ESTREAM].

   Recent attacks [CBC-ATTACK] have indicated problems with CBC-mode
   cipher suites in TLS and DTLS as well as issues with the only
   supported stream cipher (RC4) [RC4-ATTACK].  While the existing AEAD
   (AES-GCM) ciphersuites address some of these issues, concerns about
   the performance and ease of software implementation are sometimes
   raised.

   Therefore, a new stream cipher to replace RC4 and address all the
   previous issues is needed.  It is the purpose of this document to
   describe a secure stream cipher for both TLS and DTLS that is
   comparable to RC4 in speed on a wide range of platforms and can be



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   implemented easily without being vulnerable to software side-channel
   attacks.

2.  The ChaCha Cipher

   ChaCha [CHACHA] is a stream cipher developed by D.  J.  Bernstein in
   2008.  It is a refinement of Salsa20 and was used as the core of the
   SHA-3 finalist, BLAKE.

   The variant of ChaCha used in this document is ChaCha with 20 rounds,
   a 96-bit nonce and a 256 bit key, which will be referred to as
   ChaCha20 in the rest of this document.  This is the conservative
   variant (with respect to security) of the ChaCha family and is
   described in [I-D.irtf-cfrg-chacha20-poly1305].

3.  The Poly1305 Authenticator

   Poly1305 [POLY1305] is a Wegman-Carter, one-time authenticator
   designed by D.  J.  Bernstein.  Poly1305 takes a 32-byte, one-time
   key and a message and produces a 16-byte tag that authenticates the
   message such that an attacker has a negligible chance of producing a
   valid tag for an inauthentic message.  It is described in
   [I-D.irtf-cfrg-chacha20-poly1305].

4.  ChaCha20 Cipher Suites

   In the next sections different ciphersuites are defined that utilize
   the ChaCha20 cipher combined with various message authentication
   methods.

   In all cases, the ChaCha20 cipher, as in
   [I-D.irtf-cfrg-chacha20-poly1305], uses a 96-bit nonce.  That nonce
   is updated on the encryption of every TLS record, and is formed as
   follows.

       struct {
           opaque salt[4];
           opaque record_counter[8];
       } ChaChaNonce;

   The salt is generated as part of the handshake process.  It is either
   the client_write_IV (when the client is sending) or the
   server_write_IV (when the server is sending).  The salt length
   (SecurityParameters.fixed_iv_length) is 4 bytes.  The record_counter
   is the 64-bit TLS record sequence number.  In case of DTLS the
   record_counter is formed as the concatenation of the 16-bit epoch
   with the 48-bit sequence number.




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   In both TLS and DTLS the ChaChaNonce is implicit and not sent as part
   of the packet.

   The pseudorandom function (PRF) for TLS 1.2 is the TLS PRF with
   SHA-256 as the hash function.

   The RSA, DHE_RSA, ECDHE_RSA, ECDHE_ECDSA, PSK, DHE_PSK, RSA_PSK,
   ECDHE_PSK key exchanges are performed as defined in [RFC5246],
   [RFC4492], and [RFC5489].

4.1.  ChaCha20 Cipher Suites with Poly1305

   The ChaCha20 and Poly1305 primitives are built into an AEAD algorithm
   [RFC5116], AEAD_CHACHA20_POLY1305, described in
   [I-D.irtf-cfrg-chacha20-poly1305].  It takes as input a 256-bit key
   and a 96-bit nonce.

   When used in TLS, the "record_iv_length" is zero and the nonce is set
   to be the ChaChaNonce.  The additional data is seq_num +
   TLSCompressed.type + TLSCompressed.version + TLSCompressed.length,
   where "+" denotes concatenation.

   The following CipherSuites are defined.

    TLS_RSA_WITH_CHACHA20_POLY1305         = {0xTBD, 0xTBD} {0xCC, 0xA0}
    TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD} {0xCC, 0xA1}
    TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD} {0xCC, 0xA2}

    TLS_DHE_RSA_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD} {0xCC, 0xA3}
    TLS_DHE_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD} {0xCC, 0xA4}

    TLS_PSK_WITH_CHACHA20_POLY1305         = {0xTBD, 0xTBD} {0xCC, 0xA5}
    TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD} {0xCC, 0xA6}
    TLS_RSA_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD} {0xCC, 0xA7}

5.  Acknowledgements

   The authors would like to thank Zooko Wilcox-OHearn and Samuel Neves.

6.  IANA Considerations

   IANA is requested to assign the following Cipher Suites in the TLS
   Cipher Suite Registry:








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    TLS_RSA_WITH_CHACHA20_POLY1305         = {0xTBD, 0xTBD} {0xCC, 0xA0}
    TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD} {0xCC, 0xA1}
    TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD} {0xCC, 0xA2}

    TLS_DHE_RSA_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD} {0xCC, 0xA3}
    TLS_DHE_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD} {0xCC, 0xA4}

    TLS_PSK_WITH_CHACHA20_POLY1305         = {0xTBD, 0xTBD} {0xCC, 0xA5}
    TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD} {0xCC, 0xA6}
    TLS_RSA_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD} {0xCC, 0xA7}

   The ciphersuite numbers listed on the last column are numbers used
   for ciphersuite interoperability testing, and are the suggested to
   IANA to assign.

7.  Security Considerations

   ChaCha20 follows the same basic principle as Salsa20, a cipher with
   significant security review [SALSA20-SECURITY][ESTREAM].  At the time
   of writing this document, there are no known significant security
   problems with either cipher, and ChaCha20 is shown to be more
   resistant in certain attacks than Salsa20 [SALSA20-ATTACK].
   Furthermore ChaCha20 was used as the core of the BLAKE hash function,
   a SHA3 finalist, that had received considerable cryptanalytic
   attention [NIST-SHA3].

   Poly1305 is designed to ensure that forged messages are rejected with
   a probability of 1-(n/2^102) for a 16*n byte message, even after
   sending 2^64 legitimate messages.

   The cipher suites described in this document require that a nonce is
   never repeated under the same key.  The design presented ensures that
   by using the TLS sequence number which is unique and does not wrap
   [RFC5246].

   This document should not introduce any other security considerations
   than those that directly follow from the use of the stream cipher
   ChaCha20, the AEAD_CHACHA20_POLY1305 construction, (see also the
   Security Considerations section of
   [I-D.irtf-cfrg-chacha20-poly1305]).

8.  References

8.1.  Normative 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, May 2006.



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

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

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

   [I-D.irtf-cfrg-chacha20-poly1305]
              Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
              protocols", draft-irtf-cfrg-chacha20-poly1305-10 (work in
              progress), February 2015.

8.2.  Informative References

   [CHACHA]   Bernstein, D., "ChaCha, a variant of Salsa20", January
              2008, <http://cr.yp.to/chacha/chacha-20080128.pdf>.

   [POLY1305]
              Bernstein, D., "The Poly1305-AES message-authentication
              code.", March 2005,
              <http://cr.yp.to/mac/poly1305-20050329.pdf>.

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

   [SALSA20SPEC]
              Bernstein, D., "Salsa20 specification", April 2005,
              <http://cr.yp.to/snuffle/spec.pdf>.

   [SALSA20-SECURITY]
              Bernstein, D., "Salsa20 security", April 2005,
              <http://cr.yp.to/snuffle/security.pdf>.

   [ESTREAM]  Babbage, S., DeCanniere, C., Cantenaut, A., Cid, C.,
              Gilbert, H., Johansson, T., Parker, M., Preneel, B.,
              Rijmen, V., and M. Robshaw, "The eSTREAM Portfolio (rev.
              1)", September 2008,
              <http://www.ecrypt.eu.org/stream/finallist.html>.

   [CBC-ATTACK]
              AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking
              the TLS and DTLS Record Protocols", IEEE Symposium on
              Security and Privacy , 2013.






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   [RC4-ATTACK]
              Isobe, T., Ohigashi, T., Watanabe, Y., and M. Morii, "Full
              Plaintext Recovery Attack on Broadcast RC4", International
              Workshop on Fast Software Encryption , 2013.

   [SALSA20-ATTACK]
              Aumasson, J-P., Fischer, S., Khazaei, S., Meier, W., and
              C. Rechberger, "New Features of Latin Dances: Analysis of
              Salsa, ChaCha, and Rumba", 2007,
              <http://eprint.iacr.org/2007/472.pdf>.

   [NIST-SHA3]
              Chang, S., Burr, W., Kelsey, J., Paul, S., and L. Bassham,
              "Third-Round Report of the SHA-3 Cryptographic Hash
              Algorithm Competition", 2012,
              <http://dx.doi.org/10.6028/NIST.IR.7896>.

Authors' Addresses

   Adam Langley
   Google Inc

   Email: agl@google.com


   Wan-Teh Chang
   Google Inc

   Email: wtc@google.com


   Nikos Mavrogiannopoulos
   Red Hat

   Email: nmav@redhat.com


   Joachim Strombergson
   Secworks Sweden AB

   Email: joachim@secworks.se
   URI:   http://secworks.se/









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   Simon Josefsson
   SJD AB

   Email: simon@josefsson.org
   URI:   http://josefsson.org/














































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