[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02

Network Working Group                                         A. Langley
Internet-Draft                                                  W. Chang
Updates: 5246, 6347                                           Google Inc
(if approved)                                       N. Mavrogiannopoulos
Intended status: Standards Track                                 Red Hat
Expires: September 4, 2014                               J. Strombergson
                                                      Secworks Sweden AB
                                                            S. Josefsson
                                                                  SJD AB
                                                           March 3, 2014


         The ChaCha Stream Cipher for Transport Layer Security
                 draft-mavrogiannopoulos-chacha-tls-02

Abstract

   This document describes the use of the ChaCha stream cipher with
   HMAC-SHA1 and 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
   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 September 4, 2014.

Copyright Notice

   Copyright (c) 2014 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
   (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



Langley, et al.         Expires September 4, 2014               [Page 1]

Internet-Draft                 chacha-tls                     March 2014


   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
   2.  The ChaCha Cipher  . . . . . . . . . . . . . . . . . . . . . .  4
   3.  The Poly1305 Authenticator . . . . . . . . . . . . . . . . . .  5
   4.  ChaCha20 Cipher Suites . . . . . . . . . . . . . . . . . . . .  6
     4.1.  ChaCha20 Cipher Suites with HMAC-SHA1  . . . . . . . . . .  6
     4.2.  ChaCha20 Cipher Suites with Poly1305 . . . . . . . . . . .  7
   5.  Updates to the TLS Standard Stream Cipher  . . . . . . . . . .  8
   6.  Updates to DTLS  . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15




























Langley, et al.         Expires September 4, 2014               [Page 2]

Internet-Draft                 chacha-tls                     March 2014


1.  Introduction

   This document describes the use of the ChaCha stream cipher in the
   Transport Layer Security (TLS) version 1.0 [RFC2246], TLS version 1.1
   [RFC4346], and TLS version 1.2 [RFC5246] protocols, as well as in the
   Datagram Transport Layer Security (DTLS) versions 1.0 [RFC4347] and
   1.2 [RFC6347].  It can also be used with Secure Sockets Layer (SSL)
   version 3.0 [RFC6101].

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



















Langley, et al.         Expires September 4, 2014               [Page 3]

Internet-Draft                 chacha-tls                     March 2014


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.nir-cfrg-chacha20-poly1305].








































Langley, et al.         Expires September 4, 2014               [Page 4]

Internet-Draft                 chacha-tls                     March 2014


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.nir-cfrg-chacha20-poly1305].











































Langley, et al.         Expires September 4, 2014               [Page 5]

Internet-Draft                 chacha-tls                     March 2014


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.nir-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.

   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.  When used with TLS versions prior to 1.2,
   the PRF is calculated as specified in the appropriate version of the
   TLS specification.

   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 HMAC-SHA1

   The following CipherSuites are defined.












Langley, et al.         Expires September 4, 2014               [Page 6]

Internet-Draft                 chacha-tls                     March 2014


     TLS_RSA_WITH_CHACHA20_SHA              = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_CHACHA20_SHA        = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_CHACHA20_SHA      = {0xTBD, 0xTBD}

     TLS_DHE_RSA_WITH_CHACHA20_SHA          = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_CHACHA20_SHA          = {0xTBD, 0xTBD}

     TLS_PSK_WITH_CHACHA20_SHA              = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_CHACHA20_SHA        = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_CHACHA20_SHA          = {0xTBD, 0xTBD}

   The MAC algorithm used in the ciphersuites above is HMAC-SHA1
   [RFC6234].

4.2.  ChaCha20 Cipher Suites with Poly1305

   The ChaCha20 and Poly1305 primitives are built into an AEAD algorithm
   [RFC5116], AEAD_CHACHA20_POLY1305, described in
   [I-D.nir-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}
     TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}

     TLS_DHE_RSA_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD}

     TLS_PSK_WITH_CHACHA20_POLY1305         = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD}













Langley, et al.         Expires September 4, 2014               [Page 7]

Internet-Draft                 chacha-tls                     March 2014


5.  Updates to the TLS Standard Stream Cipher

   The ChaCha20 ciphersuites with HMAC-SHA1 defined in this document
   differ from the TLS RC4 ciphersuites that have been the basis for the
   definition of Standard Stream Cipher.  Unlike RC4, ChaCha20 requires
   a nonce per record.  This however, does not affect the description of
   the Standard Stream Cipher if one assumes that a nonce is optional
   and depends on the cipher's characteristics.

   Hence, this document modifies the Standard Stream Cipher by adding an
   implicit nonce.  The implicit nonce may consist of

   o  an optional fixed component ("salt"), generated from the
      key_block;

   o  a variable component, based on the 64-bit TLS record sequence
      number or the concatenation of the 16-bit epoch with the 48-bit
      sequence number in case of DTLS.

   Stream ciphers that don't require a nonce such as RC4 shall ignore
   it.  Other stream ciphers that require a nonce, such as ChaCha20 with
   HMAC-SHA1, will use the nonce and reset their state on each record.





























Langley, et al.         Expires September 4, 2014               [Page 8]

Internet-Draft                 chacha-tls                     March 2014


6.  Updates to DTLS

   The DTLS protocol requires the cipher in use to introduce no
   dependencies between TLS Records to allow lost or rearranged records.
   For that it explicitly bans stream ciphers (see Section 3.1 of
   [RFC6347]).

   As the stream cipher described in this document, unlike RC4, does not
   require dependencies between records, this ban of stream ciphers is
   lifted with this document.  Stream ciphers can be used with DTLS if
   they introduce no dependencies between records.








































Langley, et al.         Expires September 4, 2014               [Page 9]

Internet-Draft                 chacha-tls                     March 2014


7.  Acknowledgements

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
















































Langley, et al.         Expires September 4, 2014              [Page 10]

Internet-Draft                 chacha-tls                     March 2014


8.  IANA Considerations

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

     TLS_RSA_WITH_CHACHA20_POLY1305         = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}

     TLS_DHE_RSA_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD}

     TLS_PSK_WITH_CHACHA20_POLY1305         = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305   = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_CHACHA20_POLY1305     = {0xTBD, 0xTBD}

     TLS_RSA_WITH_CHACHA20_SHA              = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_CHACHA20_SHA        = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_CHACHA20_SHA      = {0xTBD, 0xTBD}

     TLS_DHE_RSA_WITH_CHACHA20_SHA          = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_CHACHA20_SHA          = {0xTBD, 0xTBD}

     TLS_PSK_WITH_CHACHA20_SHA              = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_CHACHA20_SHA        = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_CHACHA20_SHA          = {0xTBD, 0xTBD}

























Langley, et al.         Expires September 4, 2014              [Page 11]

Internet-Draft                 chacha-tls                     March 2014


9.  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 an 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, and those that
   directly follow from introducing any set of stream cipher suites into
   TLS and DTLS (see also the Security Considerations section of
   [I-D.nir-cfrg-chacha20-poly1305]).

























Langley, et al.         Expires September 4, 2014              [Page 12]

Internet-Draft                 chacha-tls                     March 2014


10.  References

10.1.  Normative References

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

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

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, 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.

   [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.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.

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

   [I-D.nir-cfrg-chacha20-poly1305]
              Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
              protocols", draft-nir-cfrg-chacha20-poly1305-01 (work in
              progress), January 2014.

10.2.  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.




Langley, et al.         Expires September 4, 2014              [Page 13]

Internet-Draft                 chacha-tls                     March 2014


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

   [RFC6101]  Freier, A., Karlton, P., and P. Kocher, "The Secure
              Sockets Layer (SSL) Protocol Version 3.0", RFC 6101,
              August 2011.

   [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.

   [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>.












Langley, et al.         Expires September 4, 2014              [Page 14]

Internet-Draft                 chacha-tls                     March 2014


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/


   Simon Josefsson
   SJD AB

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



















Langley, et al.         Expires September 4, 2014              [Page 15]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/