CPace, a balanced composable PAKE
draft-haase-cpace-01

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Network Working Group                                           B. Haase
Internet-Draft                          Endress + Hauser Liquid Analysis
Intended status: Informational                          February 7, 2020
Expires: August 10, 2020

                   CPace, a balanced composable PAKE
                          draft-haase-cpace-01

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 August 10, 2020.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
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   the Trust Legal Provisions and are provided without warranty as
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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
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  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.  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 non-prime order and
   explicitly handles the complexity of cofactor clearing on the protcol
   level.  CPace comes with a security proof providing composability
   guarantees.  As a protocol, CPace is designed to be compatible with
   so-called "x-coordinate-only" Diffie-Hellman implementations on
   elliptic curve groups.

   CPace is designed to be suitable as both, a building block within a
   larger protocol construction using CPace as substep, and as a
   standalone protocol.

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