Using cSHAKE in ORCHIDs
draft-moskowitz-orchid-cshake-00

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HIP                                                         R. Moskowitz
Internet-Draft                                            HTT Consulting
Intended status: Standards Track                                 S. Card
Expires: 13 June 2020                                    A. Wiethuechter
                                                           AX Enterprize
                                                        11 December 2019

                        Using cSHAKE in ORCHIDs
                    draft-moskowitz-orchid-cshake-00

Abstract

   This document specifies how to use the cSHAKE hash for ORCHID
   generation and allows for varying sized hashes in the ORCHID along
   with additional information within the ORCHID.  It is an addendum to
   ORCHIDv2 [RFC7343].

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terms, Notation and Definitions . . . . . . . . . . . . . . .   2
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   3
     2.2.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Adding additional information to the ORCHID . . . . . . . . .   3
   4.  ORCHID Decoding . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  ORCHID Encoding . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Initial use case for cSHAKE . . . . . . . . . . . . . . . . .   5
   7.  Initial use case for Additional Information . . . . . . . . .   5
   8.  Collision risks with Hierarchical HITs  . . . . . . . . . . .   6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   6
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     12.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Appendix A.  Calculating Collision Probabilities  . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document adds the [Keccak] based cSHAKE XOF hash function from
   NIST SP 800-185 [NIST.SP.800-185] to ORCHIDv2 [RFC7343].  cSHAKE is a
   variable output length hash function.  As such it does not need the
   truncation operation that other hashes need.  The invocation of
   cSHAKE specifies the desired number of bits in the hash output.

   cSHAKE is used, rather than SHAKE from NIST FIPS 202 [NIST.FIPS.202],
   as cSHAKE has a parameter 'S' as a customization bit string.  This
   parameter will be used for including the ORCHID Context Identifier in
   a standard fashion.

   An additional change to ORCHID construction will allow for shorter
   hash output lengths to permit inclusion of additional information
   like Hierarchical HITs [I-D.moskowitz-hip-hierarchical-hit] into the
   ORCHID.

2.  Terms, Notation and Definitions

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2.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
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