KangarooTwelve
draft-viguier-kangarootwelve-02

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Internet Research Task Force (IRTF)                           B. Viguier
Internet-Draft                                        Radboud University
Intended status: Informational                            March 19, 2018
Expires: September 20, 2018

                             KangarooTwelve
                    draft-viguier-kangarootwelve-02

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.

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   This Internet-Draft will expire on September 20, 2018.

Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   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 . . . . . . . . . . . . . . . . . . .   6
     2.3.  length_encode( x )  . . . . . . . . . . . . . . . . . . .   9
   3.  Test vectors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Pseudo code  . . . . . . . . . . . . . . . . . . . .  13
     A.1.  Keccak-p[1600,n_r=12] . . . . . . . . . . . . . . . . . .  13
     A.2.  KangarooTwelve  . . . . . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

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 has a higher speed than SHAKE
   and SHA-3.

   The SHA-3 functions process data in a serial manner and are unable to
   optimally exploit parallelism available in modern CPU architectures.
   Similar to ParallelHash [SP800-185], KangarooTwelve splits the input
   message in fragments to exploit available parallelism.  It then
   applies an inner hash function F on each of them separately before
   applying 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 Keccak-f used in SHA-3,
   making it faster than ParallelHash.  Its security builds up on the
   scrutiny that Keccak has received since its publication
   [KECCAK_CRYPTANALYSIS].

   With respect to [FIPS202] and [SP800-185] functions, KangarooTwelve
   features the following advantages:

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