(strong) AuCPace, an augmented PAKE
draft-haase-aucpace-02

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Author Bjoern Haase 
Last updated 2020-08-07
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Network Working Group                                           B. Haase
Internet-Draft                          Endress + Hauser Liquid Analysis
Intended status: Informational                            August 7, 2020
Expires: February 8, 2021

                  (strong) AuCPace, an augmented PAKE
                         draft-haase-aucpace-02

Abstract

   This document describes AuCPace which is an augmented PAKE protocol
   for two parties.  The protocol was tailored for constrained devices
   and smooth migration for compatibility with legacy user credential
   databases.  It is designed to be compatible with any group of both
   prime- and non-prime order and comes with a security proof providing
   composability guarantees.

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   the Trust Legal Provisions and are provided without warranty as
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Outcome of the CFRG PAKE selection process  . . . . . . .   3
     1.2.  Key design objectives for AuCPace . . . . . . . . . . . .   3
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Definitions for AuCPace . . . . . . . . . . . . . . . . . . .   4
     3.1.  Setup . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Access to server-side password verifiers databases  . . . . .   7
     4.1.  User credential database and password verifier types  . .   7
     4.2.  Encoding of passwords and user names  . . . . . . . . . .   8
     4.3.  AuCPace database interface for retrieving password
           verifiers . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.4.  Derivation of the salt value for strong AuCPace . . . . .  10
     4.5.  Specification of the workload parameter sigma . . . . . .  10
     4.6.  Result of the database parameter lookup . . . . . . . . .  11
   5.  Authentication session  . . . . . . . . . . . . . . . . . . .  11
     5.1.  Authentication Protocol Flow  . . . . . . . . . . . . . .  11
     5.2.  AuCPace . . . . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Authentication of transactions  . . . . . . . . . . . . . . .  14
     6.1.  Transaction Protocol Flow . . . . . . . . . . . . . . . .  14
     6.2.  AuCPace authenticated transactions  . . . . . . . . . . .  15
   7.  Ciphersuites  . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  CPACE-X25519-ELLIGATOR2_SHA512-SHA512 . . . . . . . . . .  16
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  21
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     11.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  AuCPace25519 Test Vectors  . . . . . . . . . . . . .  23
     A.1.  Inverse X25519 test vectors . . . . . . . . . . . . . . .  23
     A.2.  Strong AuCPace25519 salt test vectors . . . . . . . . . .  24
     A.3.  Test vectors for AuCPace password verifier  . . . . . . .  24
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   This document describes AuCPace which is an augmented password-
   authenticated key-establishment (PAKE) protocol for two parties.
   Both sides the client B and the server A establish a high-entropy
   session key SK, based on a secret (password) which may be of low
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