CPace, a balanced composable PAKE
draft-irtf-cfrg-cpace-00

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Last updated 2020-08-04 (latest revision 2020-07-28)
Replaces draft-haase-cpace
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Network Working Group                                         M. Abdalla
Internet-Draft                       DI, Ecole Normale Superieure, Paris
Intended status: Informational                                  B. Haase
Expires: January 29, 2021               Endress + Hauser Liquid Analysis
                                                                J. Hesse
                                        IBM, Zuerich Research Laboratory
                                                           July 28, 2020

                   CPace, a balanced composable PAKE
                        draft-irtf-cfrg-cpace-00

Abstract

   This document describes CPace which is a protocol for two parties
   that share a low-entropy secret (password) to derive a strong shared
   key without disclosing the secret to offline dictionary attacks.
   This method was tailored for constrained devices, is compatible with
   any group of both prime- and non-prime order, and comes with a
   security proof providing composability guarantees.

Status of This Memo

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   This Internet-Draft will expire on January 29, 2021.

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   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
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Abdalla, et al.         Expires January 29, 2021                [Page 1]
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Definition  CPace . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Setup . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Protocol Flow . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  CPace . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Ciphersuites  . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  CPACE-X25519-ELLIGATOR2_SHA512-SHA512 . . . . . . . . . .   9
     4.2.  CPACE-P256-SSWU_SHA256-SHA256 . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  CPace25519 Test Vectors  . . . . . . . . . . . . . .  17
     A.1.  X25519 test vectors . . . . . . . . . . . . . . . . . . .  17
     A.2.  Elligator2 test vectors . . . . . . . . . . . . . . . . .  18
     A.3.  Test vectors for the secret generator G . . . . . . . . .  19
     A.4.  Test vectors for CPace DH . . . . . . . . . . . . . . . .  20
     A.5.  Test vectors for intermediate session key generation  . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   This document describes CPace which is a protocol for two parties
   that share a low-entropy secret (password) to derive a to derive a
   strong shared key without disclosing the secret to offline dictionary
   attacks.  This preliminary working version is a renamed version of
   the earlier draft-haase-cpace-01 with minor corrections.  It has been
   uploaded for starting the work in the newly formed team of editors
   (M.  Abdalla, B.  Haase, J.  Hesse) and did not yet see a detailed
   review by M.  Abdalla and J.  Hesse.  The CPace method was tailored
   for constrained devices and specifically considers efficiency and
   hardware side-channel attack mitigations at the protocol level.
   CPace is designed to be compatible with any group of both prime- and
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