Internet DRAFT - draft-mavrogiannopoulos-chacha-tls
draft-mavrogiannopoulos-chacha-tls
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
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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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