KangarooTwelve
draft-irtf-cfrg-kangarootwelve-04

Document Type Active Internet-Draft (cfrg RG)
Authors BenoĆ®t Viguier  , David Wong  , Giles Van Assche  , Quynh Dang  , Joan Daemen 
Last updated 2020-10-26 (latest revision 2020-09-21)
Replaces draft-viguier-kangarootwelve
Stream IRTF
Intended RFC status Informational
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Crypto Forum                                                  B. Viguier
Internet-Draft                                        Radboud University
Intended status: Informational                              D. Wong, Ed.
Expires: March 25, 2021                                         Facebook
                                                      G. Van Assche, Ed.
                                                      STMicroelectronics
                                                            Q. Dang, Ed.
                                                                    NIST
                                                          J. Daemen, Ed.
                                                      Radboud University
                                                      September 21, 2020

                             KangarooTwelve
                   draft-irtf-cfrg-kangarootwelve-04

Abstract

   This document defines the KangarooTwelve eXtendable Output Function
   (XOF), a hash function with output of arbitrary 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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 March 25, 2021.

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Internet-Draft               KangarooTwelve               September 2020

Copyright Notice

   Copyright (c) 2020 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
   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  . . . . . . . . . . . . . . . . . . . .   5
     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  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Pseudocode . . . . . . . . . . . . . . . . . . . . .  14
     A.1.  Keccak-p[1600,n_r=12] . . . . . . . . . . . . . . . . . .  14
     A.2.  KangarooTwelve  . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   This document defines the KangarooTwelve eXtendable Output Function
   (XOF) [K12], i.e. a generalization of a hash function that can return
   an output of arbitrary 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 into 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

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