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Versions: 02 03 04

Network Working Group                                       S. Josefsson
Internet-Draft                                                    SJD AB
Intended status: Informational                           J. Strombergson
Expires: October 11, 2013                             Secworks Sweden AB
                                                    N. Mavrogiannopoulos
                                                               KU Leuven
                                                           April 9, 2013


         The Salsa20 Stream Cipher for Transport Layer Security
                     draft-josefsson-salsa20-tls-02

Abstract

   This document describe how the Salsa20 stream cipher can be used in
   the 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 October 11, 2013.

Copyright Notice

   Copyright (c) 2013 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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Salsa20 Cipher Suites  . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Salsa20 Cipher Suites with HMAC-SHA1 . . . . . . . . . . .  4
     2.2.  Salsa20 Cipher Suites with UMAC-96 . . . . . . . . . . . .  5
   3.  The TLS GenericStreamCipher  . . . . . . . . . . . . . . . . .  6
   4.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12


































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1.  Introduction

   This document describe how the Salsa20 stream cipher can be used 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].

   Salsa20 [SALSA20SPEC] 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
   initialization sequence and provides good key agility and
   performance.  Salsa20 is one of the ciphers selected as part of the
   eSTREAM portfolio of stream ciphers [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
   ciphersuites address these issues, concerns about their performance,
   on general purpose CPUs, are sometimes raised [AEAD-PERFORMANCE].

   Moreover, the RC4 cipher cannot be used in DTLS because it does not
   provide random access in the key stream.  That allowed no choice of a
   fast stream cipher in the context of DTLS.

   The purpose of this document is to provide an alternative stream
   cipher for both TLS and DTLS that is comparable to RC4 in speed on a
   wide range of platforms.



















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2.  Salsa20 Cipher Suites

   The following variants of Salsa20 are specified.  The variants
   provide a range of performance and security that can be selected as
   appropriate.

   ESTREAM_SALSA20:  Salsa20 with 12 rounds and a 256 bit key.  This
      cipher is the high performant eSTREAM Salsa20 with 256 bit key.

   SALSA20:  Salsa20 with 20 rounds and a 256 bit key.  This is the
      original (conservative with respect to security) variant of
      Salsa20.

   In the next sections different ciphersuites are defined that utilize
   the Salsa20 cipher combined with various MAC methods

   In all cases, 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.

2.1.  Salsa20 Cipher Suites with HMAC-SHA1

   The following CipherSuites are defined:

     TLS_RSA_WITH_ESTREAM_SALSA20_SHA1         = {0xTBD, 0xTBD}
     TLS_RSA_WITH_SALSA20_SHA1                 = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_ESTREAM_SALSA20_SHA1     = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_SALSA20_SHA1             = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_ESTREAM_SALSA20_SHA1   = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_SALSA20_SHA1           = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_SALSA20_SHA1         = {0xTBD, 0xTBD}

     TLS_PSK_WITH_ESTREAM_SALSA20_SHA1         = {0xTBD, 0xTBD}
     TLS_PSK_WITH_SALSA20_SHA1                 = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_ESTREAM_SALSA20_SHA1     = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_SALSA20_SHA1             = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_ESTREAM_SALSA20_SHA1     = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_SALSA20_SHA1             = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_ESTREAM_SALSA20_SHA1   = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_SALSA20_SHA1           = {0xTBD, 0xTBD}

   Note that Salsa20 requires a 64-bit nonce.  That nonce is updated on
   the encryption of every TLS record, and is set to be the 64-bit TLS
   record sequence number.  In case of DTLS the 64-bit nonce is formed
   as the concatenation of the 16-bit epoch with the 48-bit sequence
   number.



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   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].

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

2.2.  Salsa20 Cipher Suites with UMAC-96

   The following CipherSuites utilize Salsa20 in combination with
   UMAC-96 [RFC4418], a very fast MAC algorithm based on Universal
   Hashing.

     TLS_RSA_WITH_ESTREAM_SALSA20_UMAC96         = {0xTBD, 0xTBD}
     TLS_RSA_WITH_SALSA20_UMAC96                 = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_ESTREAM_SALSA20_UMAC96     = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_SALSA20_UMAC96             = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_ESTREAM_SALSA20_UMAC96   = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_SALSA20_UMAC96           = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_ESTREAM_SALSA20_UMAC96 = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_SALSA20_UMAC96         = {0xTBD, 0xTBD}

     TLS_PSK_WITH_ESTREAM_SALSA20_UMAC96         = {0xTBD, 0xTBD}
     TLS_PSK_WITH_SALSA20_UMAC96                 = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_ESTREAM_SALSA20_UMAC96     = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_SALSA20_UMAC96             = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_ESTREAM_SALSA20_UMAC96     = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_SALSA20_UMAC96             = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_ESTREAM_SALSA20_UMAC96   = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_SALSA20_UMAC96           = {0xTBD, 0xTBD}

   Note that both Salsa20 and UMAC-96 are used with a 64-bit nonce.
   That nonce is set to be the 64-bit TLS record sequence number.  In
   case of DTLS the 64-bit nonce is formed as the concatenation of the
   16-bit epoch with the 48-bit sequence number.

   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].












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3.  The TLS GenericStreamCipher

   The ciphersuites defined in this document differ from the TLS RC4
   ciphersuites that have been the basis for the definition of
   GenericStreamCipher.  Unlike RC4, Salsa20 requires a nonce per
   record.  This however, does not affect the description of the
   GenericStreamCipher if one assumes that a nonce is optional and
   depends on the cipher's characteristics (in that case RC4 uses a 0
   byte nonce, and Salsa20 an 8-byte nonce).

   Moreover, in order to accommodate MAC algorithms like UMAC that
   require a nonce as part of their operation, the document extends the
   MAC algorithm as specified in the TLS protocol.  The extended MAC
   includes a nonce as a second parameter.  MAC algorithms that do not
   require a nonce, such as HMAC, are assumed to ignore the nonce input
   value.  The MAC in a GenericStreamCipher is then calculated as
   follows.


         MAC(MAC_write_key, nonce,
                               seq_num +
                               TLSCompressed.type +
                               TLSCompressed.version +
                               TLSCompressed.length +
                               TLSCompressed.fragment);

   where "+" denotes concatenation.

   nonce  The nonce for this record.  If the size of the nonce accepted
      by the MAC is 64-bits then nonce equals the sequence number (or
      the concatenation of the 16-bit epoch with the 48-bit sequence
      number in DTLS).  Otherwise the MAC algorithm must specify how the
      nonce is formed.

   seq_num  The sequence number for this record.

   MAC  The MAC algorithm specified by SecurityParameters.mac_algorithm.

   As specified in TLS [RFC5246] the MAC is computed before encryption
   and the stream cipher encrypts the entire block, including the MAC.











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4.  Acknowledgements

   The authors would like to thank D. J. Bernstein, David McGrew, Wan-
   Teh Chang, and Adam Langley for discussion and suggestions.















































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5.  IANA Considerations

   IANA is requested to allocate the following numbers in the TLS Cipher
   Suite Registry:

     TLS_RSA_WITH_ESTREAM_SALSA20_SHA1           = {0xTBD, 0xTBD}
     TLS_RSA_WITH_SALSA20_SHA1                   = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_ESTREAM_SALSA20_SHA1       = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_SALSA20_SHA1               = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_ESTREAM_SALSA20_SHA1     = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_SALSA20_SHA1             = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_ESTREAM_SALSA20_SHA1   = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_SALSA20_SHA1           = {0xTBD, 0xTBD}

     TLS_PSK_WITH_ESTREAM_SALSA20_SHA1           = {0xTBD, 0xTBD}
     TLS_PSK_WITH_SALSA20_SHA1                   = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_ESTREAM_SALSA20_SHA1       = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_SALSA20_SHA1               = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_ESTREAM_SALSA20_SHA1       = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_SALSA20_SHA1               = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_ESTREAM_SALSA20_SHA1     = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_SALSA20_SHA1             = {0xTBD, 0xTBD}

     TLS_RSA_WITH_ESTREAM_SALSA20_UMAC96         = {0xTBD, 0xTBD}
     TLS_RSA_WITH_SALSA20_UMAC96                 = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_ESTREAM_SALSA20_UMAC96     = {0xTBD, 0xTBD}
     TLS_DHE_RSA_WITH_SALSA20_UMAC96             = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_ESTREAM_SALSA20_UMAC96   = {0xTBD, 0xTBD}
     TLS_ECDHE_RSA_WITH_SALSA20_UMAC96           = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_ESTREAM_SALSA20_UMAC96 = {0xTBD, 0xTBD}
     TLS_ECDHE_ECDSA_WITH_SALSA20_UMAC96         = {0xTBD, 0xTBD}

     TLS_PSK_WITH_ESTREAM_SALSA20_UMAC96         = {0xTBD, 0xTBD}
     TLS_PSK_WITH_SALSA20_UMAC96                 = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_ESTREAM_SALSA20_UMAC96     = {0xTBD, 0xTBD}
     TLS_DHE_PSK_WITH_SALSA20_UMAC96             = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_ESTREAM_SALSA20_UMAC96     = {0xTBD, 0xTBD}
     TLS_RSA_PSK_WITH_SALSA20_UMAC96             = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_ESTREAM_SALSA20_UMAC96   = {0xTBD, 0xTBD}
     TLS_ECDHE_PSK_WITH_SALSA20_UMAC96           = {0xTBD, 0xTBD}











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6.  Security Considerations

   The security of Salsa20 is discussed in the Salsa20 security
   [SALSA20-SECURITY] paper.  At the time of writing this document,
   there are no known significant security problems with the eSTREAM
   variant of Salsa20, nor with the original 20 round variant.  As of
   early 2013, the best cryptanalysis breaks 8 out of 20 rounds to
   recover the 256-bit secret key in 2^251 operations, using 2^31
   keystream pairs (see [SALSA20-ATTACK]).  For more background, see the
   eSTREAM report [ESTREAM].

   There are no ciphersuites defined in this document that utilize the
   variant of Salsa20 with 128-bit key material, because (due to the
   design of Salsa20) they provide no performance advantage over the
   256-bit variant.

   The ciphersuites that utilize UMAC-96 use a short MAC (96-bits), to
   be consistent with the MAC size used in the TLS Finished messages,
   which is also 96-bits, and thus allow room for more data in TLS
   records.  The security considerations of [RFC4418] also apply.

   This document should not introduce any other security considerations
   than those that directly follow from any use of the stream cipher
   Salsa20 and those that directly follow from introducing any set of
   stream cipher suites into TLS and DTLS.


























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7.  References

7.1.  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.

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

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, April 2006.

   [RFC4418]  Krovetz, T., "UMAC: Message Authentication Code using
              Universal Hashing", RFC 4418, March 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.

   [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.

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

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

7.2.  Informative References

   [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",
              WWW http://cr.yp.to/snuffle/security.pdf, April 2005.

   [ESTREAM]  Babbage, S., DeCanniere, C., Cantenaut, A., Cid, C.,
              Gilbert, H., Johansson, T., Parker, M., Preneel, B.,



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              Rijmen, V., and M. Robshaw, "The eSTREAM Portfolio (rev.
              1)", WWW http://www.ecrypt.eu.org/stream/finallist.html,
              September 2008.

   [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.

   [AEAD-PERFORMANCE]
              Krovetz, T. and P. Rogaway, "The Software Performance of
              Authenticated-Encryption Modes", International Workshop on
              Fast Software Encryption , 2011.

   [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",
              WWW http://eprint.iacr.org/2007/472.pdf, 2007.



























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Authors' Addresses

   Simon Josefsson
   SJD AB

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


   Joachim Strombergson
   Secworks Sweden AB

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


   Nikos Mavrogiannopoulos
   KU Leuven

   Email: nikos.mavrogiannopoulos@esat.kuleuven.be































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