The ChaCha Stream Cipher for Transport Layer Security
draft-mavrogiannopoulos-chacha-tls-03
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Adam Langley , Wan-Teh Chang , Nikos Mavrogiannopoulos , Joachim Strombergson , Simon Josefsson | ||
| Last updated | 2014-09-22 | ||
| Replaced by | draft-ietf-tls-chacha20-poly1305, draft-ietf-tls-chacha20-poly1305, RFC 7905 | ||
| Stream | (None) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-mavrogiannopoulos-chacha-tls-03
Network Working Group A. Langley
Internet-Draft W. Chang
Updates: 5246, 6347 (if approved) Google Inc
Intended status: Standards Track N. Mavrogiannopoulos
Expires: March 26, 2015 Red Hat
J. Strombergson
Secworks Sweden AB
S. Josefsson
SJD AB
September 22, 2014
The ChaCha Stream Cipher for Transport Layer Security
draft-mavrogiannopoulos-chacha-tls-03
Abstract
This document describes the use of the ChaCha stream cipher with
HMAC-SHA1 and Poly1305 in 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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 26, 2015.
Copyright Notice
Copyright (c) 2014 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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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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 HMAC-SHA1 . . . . . . . . . . 4
4.2. ChaCha20 Cipher Suites with Poly1305 . . . . . . . . . . 4
5. Updates to the TLS Standard Stream Cipher . . . . . . . . . . 5
6. Updates to DTLS . . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
This document describes the use of the ChaCha stream cipher 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].
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.
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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. 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.nir-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.nir-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.nir-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
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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.
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. When used with TLS versions prior to
1.2, the PRF is calculated as specified in the appropriate version of
the TLS specification.
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 HMAC-SHA1
The following CipherSuites are defined.
TLS_RSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_ECDHE_RSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_ECDHE_ECDSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_DHE_RSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_DHE_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_ECDHE_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_RSA_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
The MAC algorithm used in the ciphersuites above is HMAC-SHA1
[RFC6234].
4.2. ChaCha20 Cipher Suites with Poly1305
The ChaCha20 and Poly1305 primitives are built into an AEAD algorithm
[RFC5116], AEAD_CHACHA20_POLY1305, described in
[I-D.nir-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.
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TLS_RSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_DHE_RSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_DHE_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_RSA_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
5. Updates to the TLS Standard Stream Cipher
The ChaCha20 ciphersuites with HMAC-SHA1 defined in this document
differ from the TLS RC4 ciphersuites that have been the basis for the
definition of Standard Stream Cipher. Unlike RC4, ChaCha20 requires
a nonce per record. This however, does not affect the description of
the Standard Stream Cipher if one assumes that a nonce is optional
and depends on the cipher's characteristics.
Hence, this document modifies the Standard Stream Cipher by adding an
implicit nonce. The implicit nonce may consist of
o an optional fixed component ("salt"), generated from the
key_block;
o a variable component, based on the 64-bit TLS record sequence
number or the concatenation of the 16-bit epoch with the 48-bit
sequence number in case of DTLS.
Stream ciphers that don't require a nonce such as RC4 shall ignore
it. Other stream ciphers that require a nonce, such as ChaCha20 with
HMAC-SHA1, will use the nonce and reset their state on each record.
6. Updates to DTLS
The DTLS protocol requires the cipher in use to introduce no
dependencies between TLS Records to allow lost or rearranged records.
For that it explicitly bans stream ciphers (see Section 3.1 of
[RFC6347]).
As the stream cipher described in this document, unlike RC4, does not
require dependencies between records, this ban of stream ciphers is
lifted with this document. Stream ciphers can be used with DTLS if
they introduce no dependencies between records.
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7. Acknowledgements
The authors would like to thank Zooko Wilcox-OHearn and Samuel Neves.
8. IANA Considerations
IANA is requested to assign the following Cipher Suites in the TLS
Cipher Suite Registry:
TLS_RSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_DHE_RSA_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_DHE_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_RSA_PSK_WITH_CHACHA20_POLY1305 = {0xTBD, 0xTBD}
TLS_RSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_ECDHE_RSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_ECDHE_ECDSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_DHE_RSA_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_DHE_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_ECDHE_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
TLS_RSA_PSK_WITH_CHACHA20_SHA = {0xTBD, 0xTBD}
9. 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
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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, and those that
directly follow from introducing any set of stream cipher suites into
TLS and DTLS (see also the Security Considerations section of
[I-D.nir-cfrg-chacha20-poly1305]).
10. References
10.1. 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.
[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.
[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.
[RFC6234] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[I-D.nir-cfrg-chacha20-poly1305]
Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
protocols", draft-nir-cfrg-chacha20-poly1305-01 (work in
progress), January 2014.
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10.2. 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>.
[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", 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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