ChaCha20 and Poly1305 based Cipher Suites for TLS
draft-agl-tls-chacha20poly1305-03

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Network Working Group                                         A. Langley
Internet-Draft                                                  W. Chang
Expires: May 5, 2014                                          Google Inc
                                                                Nov 2013

           ChaCha20 and Poly1305 based Cipher Suites for TLS
                   draft-agl-tls-chacha20poly1305-03

Abstract

   This memo describes the use of the ChaCha20 cipher with a Poly1305
   authenticator in 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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 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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   (http://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
   3.  ChaCha20 . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Poly1305 . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  AEAD construction  . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Cipher suites  . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Test vectors . . . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 16
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17

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1.  Introduction

   Existing TLS [RFC5246] cipher suites either suffer from cryptographic
   weaknesses (RC4), major implementation pitfalls (CBC mode block
   ciphers) or are difficult to efficiently and securely 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 16, 32-bit output words.  By
   convention, 8 of the input words consist of a 256-bit key, 4 are
   constants and the remaining four are an nonce and block counter.  The
   output words are converted to bytes and XORed with the plaintext to
   produce ciphertext.  In order to generate sufficient output bytes to
   XOR with the whole plaintext, the block counter is incremented and
   ChaCha20 is run again, as many times as needed, for up to 2^70 bytes