Network Working Group S. Josefsson
Internet-Draft SJD AB
Intended status: Informational J. Strombergson
Expires: September 19, 2013 Secworks Sweden AB
N. Mavrogiannopoulos
KU Leuven
March 18, 2013
The Salsa20 Stream Cipher for Transport Layer Security (TLS) and
Datagram Transport Layer Security (DTLS)
draft-josefsson-salsa20-tls-01
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Salsa20 Cipher Suites . . . . . . . . . . . . . . . . . . . . 4
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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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. The cipher has been designed to minimize risk due to
side channel attacks. The cipher has trivial initialization sequence
and provides good key agility and good performance over a range of
data sizes. Salsa20 is one of the ciphers selected as part of the
eSTREAM portolio 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 AEAD ciphersuites
address these issues, concerns about their performance, on general
purpose CPUs, are sometimes raised.
Moreover, the RC4 cipher could not be used in DTLS because it did 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.
SALSA20R12: Salsa20 with 12 rounds and a 256 bit key. This cipher
corresponds to the eSTREAM Salsa20 with 256 bit key.
SALSA20R20: Salsa20 with 20 rounds and a 256 bit key. This is a
higher security variant of Salsa20.
The following ciphersuites are defined:
CipherSuite TLS_RSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_RSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_RSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_RSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_RSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_RSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_ECDSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_ECDSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_PSK_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_PSK_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_RSA_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_RSA_PSK_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_PSK_WITH_SALSA20R20_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.
The RSA, DHE_RSA, ECDHE_RSA, ECDHE_ECDSA, PSK, DHE_PSK, RSA_PSK,
ECDHE_PSK key exchanges are performed as defined in RFC 5246, RFC
4492 and RFC 5489.
The MAC algorithm to use is HMAC-SHA1 [RFC6234]. [[[XXX: For better
performance, we consider the use of UMAC-AES-96, UMAC-AES-128
[RFC4418] or Poly1305 instead of HMAC-SHA1.]]]
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.
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PSK cipher suites for TLS are described in RFC 5487 as to SHA-256/384
and RFC 5489 as to ECDHE_PSK.
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3. Acknowledgements
The authors would like to thank D. J. Bernstein, David McGrew, and
Wan-Teh Chang for discussion and suggestions.
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4. IANA Considerations
IANA is requested to allocate the following numbers in the TLS Cipher
Suite Registry:
CipherSuite TLS_RSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_RSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_RSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_RSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_RSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_RSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_ECDSA_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_ECDSA_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_PSK_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_DHE_PSK_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_RSA_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_RSA_PSK_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_PSK_WITH_SALSA20R12_SHA1 = {0xTBD, 0xTBD}
CipherSuite TLS_ECDHE_PSK_WITH_SALSA20R20_SHA1 = {0xTBD, 0xTBD}
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5. Security Considerations
The security of Salsa20 is discussed in the Salsa20 security
[SALSA20-SECURITY] paper. The reader must consult cryptographic
research to find out the current security status of Salsa20. At the
time of writing this document, there are no known significant
security problems with Salsa20/12 or Salsa20/20. 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.
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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6. References
6.1. 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.
[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.
6.2. Informative References
[RFC4418] Krovetz, T., "UMAC: Message Authentication Code using
Universal Hashing", RFC 4418, March 2006.
[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.,
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
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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",
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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