Internet DRAFT - draft-ietf-tls-chacha20-poly1305
draft-ietf-tls-chacha20-poly1305
Network Working Group A. Langley
Internet-Draft W. Chang
Updates: 5246, 6347 (if approved) Google Inc
Intended status: Standards Track N. Mavrogiannopoulos
Expires: June 18, 2016 Red Hat
J. Strombergson
Secworks Sweden AB
S. Josefsson
SJD AB
December 16, 2015
ChaCha20-Poly1305 Cipher Suites for Transport Layer Security (TLS)
draft-ietf-tls-chacha20-poly1305-04
Abstract
This document describes the use of the ChaCha stream cipher and
Poly1305 authenticator in the 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. ChaCha20 Cipher Suites . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document describes the use of the ChaCha stream cipher and
Poly1305 authenticator in version 1.2 or later of the the Transport
Layer Security (TLS) [RFC5246] protocol, as well as version 1.2 or
later of the Datagram Transport Layer Security (DTLS) protocol
[RFC6347].
ChaCha [CHACHA] is a stream cipher developed by D. J. Bernstein in
2008. It is a refinement of Salsa20, which is one of the selected
ciphers in the eSTREAM portfolio [ESTREAM], and was used as the core
of the SHA-3 finalist, BLAKE.
The variant of ChaCha used in this document has 20 rounds, a 96-bit
nonce and a 256-bit key, and will be referred to as ChaCha20. This
is the conservative variant (with respect to security) of the ChaCha
family and is described in [RFC7539].
Poly1305 [POLY1305] is a Wegman-Carter, one-time authenticator
designed by D. J. Bernstein. Poly1305 takes a 256-bit, 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 also described in
[RFC7539].
ChaCha and Poly1305 have both been designed for high performance in
software implementations. They typically admit a compact
implementation that uses few resources and inexpensive operations,
which makes them suitable on a wide range of architectures. They
have also been designed to minimize leakage of information through
side channels.
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Recent attacks [CBC-ATTACK] have indicated problems with the 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
cipher suites (based on AES-GCM) address some of these issues, there
are concerns about their performance and ease of software
implementation.
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.
2. ChaCha20 Cipher Suites
The ChaCha20 and Poly1305 primitives are built into an AEAD algorithm
[RFC5116], AEAD_CHACHA20_POLY1305, as described in [RFC7539]. This
AEAD is incorporated into TLS and DTLS as specified in section
6.2.3.3 of [RFC5246].
AEAD_CHACHA20_POLY1305 requires a 96-bit nonce, which is formed as
follows:
1. The 64-bit record sequence number is serialized as an 8-byte,
big-endian value and padded on the left with four 0x00 bytes.
2. The padded sequence number is XORed with the client_write_IV
(when the client is sending) or server_write_IV (when the server
is sending).
In DTLS, the 64-bit seq_num is the 16-bit epoch concatenated with the
48-bit seq_num.
This nonce construction is different from the one used with AES-GCM
in TLS 1.2 but matches the scheme expected to be used in TLS 1.3.
The nonce is constructed from the record sequence number and shared
secret, both of which are known to the recipient. The advantage is
that no per-record, explicit nonce need be transmitted, which saves
eight bytes per record and prevents implementations from mistakenly
using a random nonce. Thus, in the terms of [RFC5246],
SecurityParameters.fixed_iv_length is twelve bytes and
SecurityParameters.record_iv_length is zero bytes.
The following cipher suites are defined.
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TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD}
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD}
TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD}
TLS_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD}
TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD}
TLS_DHE_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD}
TLS_RSA_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD}
The DHE_RSA, ECDHE_RSA, ECDHE_ECDSA, PSK, ECDHE_PSK, DHE_PSK and
RSA_PSK key exchanges for these cipher suites are unaltered and thus
are performed as defined in [RFC5246], [RFC4492], and [RFC5489].
The pseudorandom function (PRF) for all the cipher suites defined in
this document is the TLS PRF with SHA-256 as the hash function.
3. IANA Considerations
IANA is requested to add the following entries in the TLS Cipher
Suite Registry:
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD} {0xCC, 0xA8}
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD} {0xCC, 0xA9}
TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD} {0xCC, 0xAA}
TLS_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD} {0xCC, 0xAB}
TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD} {0xCC, 0xAC}
TLS_DHE_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD} {0xCC, 0xAD}
TLS_RSA_PSK_WITH_CHACHA20_POLY1305_SHA256 = {0xTBD, 0xTBD} {0xCC, 0xAE}
The cipher suite numbers listed in the second column are numbers used
for cipher suite interoperability testing and it's suggested that
IANA use these values for assignment.
4. Security Considerations
ChaCha20 follows the same basic principle as Salsa20[SALSA20SPEC], 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 has received considerable
cryptanalytic attention [NIST-SHA3].
Poly1305 is designed to ensure that forged messages are rejected with
a probability of 1-(n/2^107), where n is the maximum length of the
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input to Poly1305. In the case of (D)TLS, this means a maximum
forgery probability of about 1 in 2^93.
The cipher suites described in this document require that a nonce is
never repeated under the same key. The design presented ensures this
by using the TLS sequence number, which is unique and does not wrap
[RFC5246].
It should be noted that AEADs, such as ChaCha20-Poly1305, are not
intended to hide the lengths of plaintexts. When this document
speaks of side-channel attacks, it is not considering traffic
analysis, but rather timing and cache side-channels. Traffic
analysis, while a valid concern, is outside the scope of the AEAD and
is being addressed elsewhere in future versions of TLS.
Otherwise, this document should not introduce any additional security
considerations other than those that follow from the use of the
AEAD_CHACHA20_POLY1305 construction, thus the reader is directed to
the Security Considerations section of [RFC7539].
5. Acknowledgements
The authors would like to thank Zooko Wilcox-OHearn, Samuel Neves and
Colm MacCarthaigh for their suggestions and guidance.
6. References
6.1. 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,
DOI 10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5489] Badra, M. and I. Hajjeh, "ECDHE_PSK Cipher Suites for
Transport Layer Security (TLS)", RFC 5489,
DOI 10.17487/RFC5489, March 2009,
<http://www.rfc-editor.org/info/rfc5489>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
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[RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<http://www.rfc-editor.org/info/rfc7539>.
6.2. 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, DOI 10.17487/RFC5116, January 2008,
<http://www.rfc-editor.org/info/rfc5116>.
[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.
[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>.
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[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/
Simon Josefsson
SJD AB
Email: simon@josefsson.org
URI: http://josefsson.org/
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