Oblivious Pseudorandom Functions (OPRFs) using Prime-Order Groups
draft-irtf-cfrg-voprf-06

Document Type Active Internet-Draft (cfrg RG)
Authors Alex Davidson  , Armando Faz-Hern├índez  , Nick Sullivan  , Christopher Wood 
Last updated 2021-02-21
Replaces draft-sullivan-cfrg-voprf
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Network Working Group                                        A. Davidson
Internet-Draft                                                          
Intended status: Informational                          A. Faz-Hernandez
Expires: 25 August 2021                                      N. Sullivan
                                                               C.A. Wood
                                                              Cloudflare
                                                        21 February 2021

   Oblivious Pseudorandom Functions (OPRFs) using Prime-Order Groups
                        draft-irtf-cfrg-voprf-06

Abstract

   An Oblivious Pseudorandom Function (OPRF) is a two-party protocol for
   computing the output of a PRF.  One party (the server) holds the PRF
   secret key, and the other (the client) holds the PRF input.  The
   'obliviousness' property ensures that the server does not learn
   anything about the client's input during the evaluation.  The client
   should also not learn anything about the server's secret PRF key.
   Optionally, OPRFs can also satisfy a notion 'verifiability' (VOPRF).
   In this setting, the client can verify that the server's output is
   indeed the result of evaluating the underlying PRF with just a public
   key.  This document specifies OPRF and VOPRF constructions
   instantiated within prime-order groups, including elliptic curves.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/cfrg/draft-irtf-cfrg-voprf.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Davidson, et al.         Expires 25 August 2021                 [Page 1]
Internet-Draft                    OPRFs                    February 2021

   This Internet-Draft will expire on 25 August 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Change log  . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Preliminaries . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Prime-Order Group Dependency  . . . . . . . . . . . . . .   7
     2.2.  Other Conventions . . . . . . . . . . . . . . . . . . . .   8
   3.  OPRF Protocol . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.2.  Context Setup . . . . . . . . . . . . . . . . . . . . . .  10
     3.3.  Data Types  . . . . . . . . . . . . . . . . . . . . . . .  11
     3.4.  Context APIs  . . . . . . . . . . . . . . . . . . . . . .  11
       3.4.1.  Server Context  . . . . . . . . . . . . . . . . . . .  11
       3.4.2.  VerifiableServerContext . . . . . . . . . . . . . . .  13
       3.4.3.  Client Context  . . . . . . . . . . . . . . . . . . .  18
       3.4.4.  VerifiableClientContext . . . . . . . . . . . . . . .  20
   4.  Domain Separation . . . . . . . . . . . . . . . . . . . . . .  23
   5.  Ciphersuites  . . . . . . . . . . . . . . . . . . . . . . . .  23
     5.1.  OPRF(ristretto255, SHA-512) . . . . . . . . . . . . . . .  23
     5.2.  OPRF(decaf448, SHA-512) . . . . . . . . . . . . . . . . .  24
     5.3.  OPRF(P-256, SHA-256)  . . . . . . . . . . . . . . . . . .  24
     5.4.  OPRF(P-384, SHA-512)  . . . . . . . . . . . . . . . . . .  25
     5.5.  OPRF(P-521, SHA-512)  . . . . . . . . . . . . . . . . . .  25
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
     6.1.  Security Properties . . . . . . . . . . . . . . . . . . .  26
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