ChaCha20 and Poly1305 for IETF Protocols
RFC 7539

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Internet Research Task Force (IRTF)                               Y. Nir
Request for Comments: 7539                                   Check Point
Category: Informational                                       A. Langley
ISSN: 2070-1721                                             Google, Inc.
                                                                May 2015

                ChaCha20 and Poly1305 for IETF Protocols

Abstract

   This document defines the ChaCha20 stream cipher as well as the use
   of the Poly1305 authenticator, both as stand-alone algorithms and as
   a "combined mode", or Authenticated Encryption with Associated Data
   (AEAD) algorithm.

   This document does not introduce any new crypto, but is meant to
   serve as a stable reference and an implementation guide.  It is a
   product of the Crypto Forum Research Group (CFRG).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Research Task Force
   (IRTF).  The IRTF publishes the results of Internet-related research
   and development activities.  These results might not be suitable for
   deployment.  This RFC represents the consensus of the Crypto Forum
   Research Group of the Internet Research Task Force (IRTF).  Documents
   approved for publication by the IRSG are not a candidate for any
   level of Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7539.

Copyright Notice

   Copyright (c) 2015 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
   to this document.

Nir & Langley                 Informational                     [Page 1]
RFC 7539                   ChaCha20 & Poly1305                  May 2015

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................4
   2. The Algorithms ..................................................4
      2.1. The ChaCha Quarter Round ...................................4
           2.1.1. Test Vector for the ChaCha Quarter Round ............5
      2.2. A Quarter Round on the ChaCha State ........................5
           2.2.1. Test Vector for the Quarter Round on the
                  ChaCha State ........................................6
      2.3. The ChaCha20 Block Function ................................6
           2.3.1. The ChaCha20 Block Function in Pseudocode ...........8
           2.3.2. Test Vector for the ChaCha20 Block Function .........9
      2.4. The ChaCha20 Encryption Algorithm .........................10
           2.4.1. The ChaCha20 Encryption Algorithm in Pseudocode ....11
           2.4.2. Example and Test Vector for the ChaCha20 Cipher ....11
      2.5. The Poly1305 Algorithm ....................................13
           2.5.1. The Poly1305 Algorithms in Pseudocode ..............15
           2.5.2. Poly1305 Example and Test Vector ...................15
      2.6. Generating the Poly1305 Key Using ChaCha20 ................17
           2.6.1. Poly1305 Key Generation in Pseudocode ..............18
           2.6.2. Poly1305 Key Generation Test Vector ................18
      2.7. A Pseudorandom Function for Crypto Suites based on
           ChaCha/Poly1305 ...........................................18
      2.8. AEAD Construction .........................................19
           2.8.1. Pseudocode for the AEAD Construction ...............21
           2.8.2. Example and Test Vector for
                  AEAD_CHACHA20_POLY1305 .............................22
   3. Implementation Advice ..........................................24
   4. Security Considerations ........................................24
   5. IANA Considerations ............................................26
   6. References .....................................................26
      6.1. Normative References ......................................26
      6.2. Informative References ....................................26
   Appendix A. Additional Test Vectors ...............................29
     A.1. The ChaCha20 Block Functions ...............................29
     A.2. ChaCha20 Encryption ........................................32
     A.3. Poly1305 Message Authentication Code .......................34
     A.4. Poly1305 Key Generation Using ChaCha20 .....................40
     A.5. ChaCha20-Poly1305 AEAD Decryption ..........................41