Using ChaCha20-Poly1305 Authenticated Encryption in the Cryptographic Message Syntax (CMS)

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Document Type Active Internet-Draft (curdle WG)
Last updated 2016-12-16 (latest revision 2016-12-01)
Replaces draft-housley-cms-chacha20-poly1305
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Internet-Draft                                                R. Housley
Intended status: Standards Track                          Vigil Security
Expires: 1 June 2017                                     1 December 2016

             Using ChaCha20-Poly1305 Authenticated Encryption
                 in the Cryptographic Message Syntax (CMS)



   This document describes the conventions for using ChaCha20-Poly1305
   Authenticated Encryption in the Cryptographic Message Syntax (CMS).
   ChaCha20-Poly1305 is an authenticated encryption algorithm
   constructed of the ChaCha stream cipher and Poly1305 authenticator.

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Housley           Using AEAD_CHACHA20_POLY1305 with CMS         [Page 1]
Internet-Draft                                           1 December 2016

1.  Introduction

   This document specifies the conventions for using the
   ChaCha20-Poly1305 Authenticated Encryption as the content-
   authenticated-encryption algorithm with the Cryptographic Message
   Syntax (CMS) [CMS] authenticated-enveloped-data content type

   ChaCha [CHACHA] is a stream cipher developed by D. J. Bernstein in
   2008.  It is a refinement of Salsa20, which is one of the ciphers in
   the eSTREAM portfolio [ESTREAM].

   ChaCha20 is the 20-round variant of ChaCha; it requires a 256-bit key
   and a 96-bit nonce.  ChaCha20 is described in [FORIETF].

   Poly1305 [POLY1305] is a Wegman-Carter, one-time authenticator
   designed by D. J. Bernstein.  Poly1305 produces a 16-byte
   authentication tag; it requires a 256-bit, single-use key.  Poly1305
   is also described in [FORIETF].

   ChaCha20 and Poly1305 have been designed for high performance
   software implementations.  They can typically be implemented with few
   resources and inexpensive operations, making them suitable on a wide
   range of systems.  They have also been designed to minimize leakage
   of information through side channels.

1.1.  The ChaCha20 and Poly1305 AEAD Construction

   ChaCha20 and Poly1305 have been combined to create an Authenticated
   Encryption with Associated Data (AEAD) algorithm [AEAD].  This AEAD
   algorithm is often referred to as AEAD_CHACHA20_POLY1305, and it is
   described [FORIETF].

   AEAD_CHACHA20_POLY1305 accepts four inputs: a 256-bit key, a 96-bit
   nonce, an arbitrary length plaintext, and an arbitrary length
   additional authenticated data (AAD).  As the name implies, a nonce
   value cannot be used securely more than once with the same key.

   AEAD_CHACHA20_POLY1305 produces two outputs: ciphertext of the same
   length as the plaintext and a 128-bit authentication tag.

   AEAD_CHACHA20_POLY1305 authenticated decryption processing is similar
   to the encryption processing.  Of course, the roles of ciphertext and
   plaintext are reversed, so the ChaCha20 encryption function is
   applied to the ciphertext, producing the plaintext.  The Poly1305
   function is run over the AAD and the ciphertext, not the plaintext,
   and the resulting authentication tag is bitwise compared to the
   received authentication tag.  The message is authenticated if and

Housley           Using AEAD_CHACHA20_POLY1305 with CMS         [Page 2]
Internet-Draft                                           1 December 2016

   only if the calculated and received authentication tags match.

1.2.  ASN.1

   CMS values are generated using ASN.1 [X680], which uses the Basic
   Encoding Rules (BER) and the Distinguished Encoding Rules (DER)

1.3.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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