KangarooTwelve
draft-viguier-kangarootwelve-00

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Internet Research Task Force (IRTF)                           B. Viguier
Internet-Draft                                        Radboud University
Intended status: Informational                             June 14, 2017
Expires: December 16, 2017

                             KangarooTwelve
                    draft-viguier-kangarootwelve-00

Abstract

   This document defines the KangarooTwelve eXtendable Output Function
   (XOF), a hash function with arbitrary output length.  It provides an
   efficient and secure hashing primitive, which is able to exploit the
   parallelism of the implementation in a scalable way.  It uses tree
   hashing over a round-reduced version of SHAKE128 as underlying
   primitive.

   This document builds up on the definitions of the permutations and of
   the sponge construction in [FIPS 202], and is meant to serve as a
   stable reference and an implementation guide.

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 December 16, 2017.

Copyright Notice

   Copyright (c) 2017 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

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Internet-Draft               KangarooTwelve                    June 2017

   carefully, as they describe your rights and restrictions with respect
   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
     1.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Inner function: F . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Tree hashing over F . . . . . . . . . . . . . . . . . . .   5
     2.3.  right_encode( x ) . . . . . . . . . . . . . . . . . . . .   7
   3.  Test vectors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Pseudo code  . . . . . . . . . . . . . . . . . . . .  11
     A.1.  Keccak-p[1600] over 12 rounds . . . . . . . . . . . . . .  11
     A.2.  Inner function F  . . . . . . . . . . . . . . . . . . . .  12
     A.3.  KangarooTwelve  . . . . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   This document defines the KangarooTwelve eXtendable Output Function
   (XOF) [K12], i.e. a generalization of a hash function that can return
   arbitrary output length.  KangarooTwelve is based on a Keccak-p
   permutation specified in [FIPS202] and aims at higher speed than
   SHAKE and SHA-3.

   The SHA-3 functions process data in a serial manner and unable to
   optimally exploit parallelism available in modern CPU architectures.
   KangarooTwelve splits the input message in fragments and applies an
   inner hash function F on each of them separately.  It then applies F
   again on the concatenation of the digests.  It makes use of Sakura
   coding for ensuring soundness of the tree hashing mode [SAKURA].  The
   inner hash function F is a sponge function and uses a round-reduced
   version of the permutation used in Keccak.  Its security builds up on
   the scrutiny that Keccak has received since its publication
   [KECCAK_CRYPTANALYSIS].

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