ChaCha20 and Poly1305 based Cipher Suites for TLS
draft-agl-tls-chacha20poly1305-00

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Author Adam Langley 
Last updated 2013-09-10
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Network Working Group                                         A. Langley
Internet-Draft                                                Google Inc
Expires: March 5, 2014                                         Sept 2013

           ChaCha20 and Poly1305 based Cipher Suites for TLS
                   draft-agl-tls-chacha20poly1305-00

Abstract

   This memo describes the use of the ChaCha20 cipher with a Poly1305
   authenticator as a cipher suite for Transport Layer Security (TLS).

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
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   This Internet-Draft will expire on March 5, 2014.

Copyright Notice

   Copyright (c) 2013 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
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
   3.  ChaCha20 . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Poly1305 . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  AEAD construction  . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Cipher suites  . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Test vectors . . . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   10. Normative References . . . . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15

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1.  Introduction

   Existing TLS [RFC5246] cipher suites either suffer from cryptographic
   weaknesses (RC4), major implementation pitfalls (CBC mode ciphers) or
   are difficult to effectively implement in software (AES-GCM).  In
   order to improve the state of software TLS implementations, this memo
   specifies cipher suites that can be fast and secure when implemented
   in software without sacrificing key agility.

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2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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3.  ChaCha20

   ChaCha20 [chacha] is a stream cipher developed by D. J. Bernstein.
   It is a refinement of Salsa20 and was used as the core of the SHA-3
   finalist, BLAKE.

   ChaCha20 maps 16, 32-bit input words to 64 output bytes.  By
   convention, 8 of the input words consist of a 256-bit key, 4 are
   constants and the remaining four are a block counter.  The output
   bytes are XORed with the plaintext to produce ciphertext.

   ChaCha20 consists of 20 rounds, alternating between "column" rounds
   and "diagonal" rounds.  Each round applies the following "quarter-
   round" function four times.  The quarter-round function updates 4,
   32-bit words (a, b, c, d) as follows:

   a += b; d ^= a; d <<<= 16;
   c += d; b ^= c; b <<<= 12;
   a += b; d ^= a; d <<<= 8;
   c += d; b ^= c; b <<<= 7;

   The 16 input words are conceptually arranged in a four by four grid
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