Oblivious Pseudorandom Functions (OPRFs) using Prime-Order Groups
draft-irtf-cfrg-voprf-00

Document Type Active Internet-Draft (cfrg RG)
Last updated 2019-07-08
Stream IRTF
Intended RFC status (None)
Formats plain text pdf html bibtex
Stream IRTF state Active RG Document
Consensus Boilerplate Unknown
Document shepherd No shepherd assigned
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
Network Working Group                                        A. Davidson
Internet-Draft                                               N. Sullivan
Intended status: Informational                                Cloudflare
Expires: January 9, 2020                                         C. Wood
                                                              Apple Inc.
                                                           July 08, 2019

   Oblivious Pseudorandom Functions (OPRFs) using Prime-Order Groups
                        draft-irtf-cfrg-voprf-00

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.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 9, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Davidson, et al.         Expires January 9, 2020                [Page 1]
Internet-Draft                    OPRFs                        July 2019

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Security Properties . . . . . . . . . . . . . . . . . . . . .   5
   4.  OPRF Protocol . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Protocol correctness  . . . . . . . . . . . . . . . . . .   8
     4.2.  Instantiations of GG  . . . . . . . . . . . . . . . . . .   9
     4.3.  OPRF algorithms . . . . . . . . . . . . . . . . . . . . .   9
       4.3.1.  OPRF_Setup  . . . . . . . . . . . . . . . . . . . . .  10
       4.3.2.  OPRF_Blind  . . . . . . . . . . . . . . . . . . . . .  10
       4.3.3.  OPRF_Eval . . . . . . . . . . . . . . . . . . . . . .  10
       4.3.4.  OPRF_Unblind  . . . . . . . . . . . . . . . . . . . .  11
       4.3.5.  OPRF_Finalize . . . . . . . . . . . . . . . . . . . .  11
     4.4.  VOPRF algorithms  . . . . . . . . . . . . . . . . . . . .  12
       4.4.1.  VOPRF_Setup . . . . . . . . . . . . . . . . . . . . .  12
       4.4.2.  VOPRF_Blind . . . . . . . . . . . . . . . . . . . . .  13
       4.4.3.  VOPRF_Eval  . . . . . . . . . . . . . . . . . . . . .  13
       4.4.4.  VOPRF_Unblind . . . . . . . . . . . . . . . . . . . .  13
       4.4.5.  VOPRF_Finalize  . . . . . . . . . . . . . . . . . . .  14
     4.5.  Utility algorithms  . . . . . . . . . . . . . . . . . . .  14
       4.5.1.  bin2scalar  . . . . . . . . . . . . . . . . . . . . .  14
     4.6.  Efficiency gains with pre-processing and fixed-base
           blinding  . . . . . . . . . . . . . . . . . . . . . . . .  15
       4.6.1.  OPRF_Preprocess . . . . . . . . . . . . . . . . . . .  16
       4.6.2.  OPRF_Blind  . . . . . . . . . . . . . . . . . . . . .  16
       4.6.3.  OPRF_Unblind  . . . . . . . . . . . . . . . . . . . .  16
   5.  NIZK Discrete Logarithm Equality Proof  . . . . . . . . . . .  17
     5.1.  DLEQ_Generate . . . . . . . . . . . . . . . . . . . . . .  17
Show full document text