Internet DRAFT - draft-josefsson-salsa20-tls
draft-josefsson-salsa20-tls
Network Working Group S. Josefsson
Internet-Draft SJD AB
Intended status: Informational J. Strombergson
Expires: May 31, 2014 Secworks Sweden AB
N. Mavrogiannopoulos
Red Hat
November 27, 2013
The Salsa20 Stream Cipher for Transport Layer Security
draft-josefsson-salsa20-tls-04
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
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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Salsa20 Cipher Suites . . . . . . . . . . . . . . . . . . . . 3
2.1. Salsa20 Cipher Suites with HMAC-SHA1 . . . . . . . . . . 3
3. The TLS GenericStreamCipher . . . . . . . . . . . . . . . . . 4
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Algorithm Selection Background . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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 and fast key
setup and provides good overall 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,
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on general purpose CPUs, are sometimes raised [AEAD-PERFORMANCE].
Moreover, the DTLS protocol cannot take advantage of the fast RC4
stream cipher because it does not provide random access in the key
stream.
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.
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: (note that the third column
contains the suggested to IANA ciphersuite numbers)
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TLS_RSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x10}
TLS_RSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x11}
TLS_ECDHE_RSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x12}
TLS_ECDHE_RSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x13}
TLS_ECDHE_ECDSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x14}
TLS_ECDHE_ECDSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x15}
TLS_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x16}
TLS_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x17}
TLS_ECDHE_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x18}
TLS_ECDHE_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x19}
TLS_RSA_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1A}
TLS_RSA_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1B}
TLS_DHE_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1C}
TLS_DHE_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1D}
TLS_DHE_RSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1E}
TLS_DHE_RSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1F}
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.
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].
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).
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.
5. IANA Considerations
IANA is requested to allocate the following numbers in the TLS Cipher
Suite Registry (note that the third column contains the suggested
ciphersuite numbers):
TLS_RSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x10}
TLS_RSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x11}
TLS_ECDHE_RSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x12}
TLS_ECDHE_RSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x13}
TLS_ECDHE_ECDSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x14}
TLS_ECDHE_ECDSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x15}
TLS_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x16}
TLS_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x17}
TLS_ECDHE_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x18}
TLS_ECDHE_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x19}
TLS_RSA_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1A}
TLS_RSA_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1B}
TLS_DHE_PSK_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1C}
TLS_DHE_PSK_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1D}
TLS_DHE_RSA_WITH_ESTREAM_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1E}
TLS_DHE_RSA_WITH_SALSA20_SHA1 = {0xTBD, 0xTBD} {0xE4, 0x1F}
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].
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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.
7. Algorithm Selection Background
This draft uses Salsa20, a winner of an international competion of
stream ciphers (eStream), which is easily implementable without
leaking information through side-channels, i.e. timing and power
attacks.
Suggestions has been made to instead use Chacha [CHACHASPEC], a
derivative of Salsa20 that has been shown to be 7% faster in hardware
and occupy 10% less space [VLSI-IMPL]. In our opinion the
performance benefits don't justify switching from a winner of an
international competition to another algorithm (even if it is a
derivative of it).
This draft adds a new cipher to existing TLS and DTLS implementations
which is combined with the existing MAC algorithms in TLS (i.e.,
HMAC-SHA1). That allows the new cipher to replace the, currently
known to be broken, RC4 ciphersuites, in all TLS versions.
8. References
8.1. 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.
[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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[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.
8.2. 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.,
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]
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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.
[CHACHASPEC]
Bernstein, D., "ChaCha, a variant of Salsa20", WWW
http://cr.yp.to/chacha/chacha-20080128.pdf, January 2008.
[VLSI-IMPL]
Henzen, L., Carbognani, F., and W. Fichtner, "VLSI
hardware evaluation of the stream ciphers Salsa20 and
ChaCha, and the compression function Rumba.", 2008.
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
Red Hat
Email: nmav@redhat.com
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