Privacy Pass: The Protocol
draft-davidson-pp-protocol-01

Document Type Active Internet-Draft (candidate for privacypass WG)
Last updated 2020-08-10 (latest revision 2020-07-13)
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Network Working Group                                        A. Davidson
Internet-Draft                                                Cloudflare
Intended status: Informational                              13 July 2020
Expires: 14 January 2021

                       Privacy Pass: The Protocol
                     draft-davidson-pp-protocol-01

Abstract

   This document specifies the Privacy Pass protocol.  This protocol
   provides anonymity-preserving authorization of clients to servers.
   In particular, client re-authorization events cannot be linked to any
   previous initial authorization.  Privacy Pass is intended to be used
   as a performant protocol in the application-layer.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 14 January 2021.

Copyright Notice

   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
   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
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   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Davidson                 Expires 14 January 2021                [Page 1]
Internet-Draft                 PP protocol                     July 2020

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Motivating use-cases  . . . . . . . . . . . . . . . . . .   4
     3.2.  Anonymity and security guarantees . . . . . . . . . . . .   5
     3.3.  Basic assumptions . . . . . . . . . . . . . . . . . . . .   5
   4.  Protocol description  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Server setup  . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Client setup  . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Issuance phase  . . . . . . . . . . . . . . . . . . . . .   6
     4.4.  Redemption phase  . . . . . . . . . . . . . . . . . . . .   6
       4.4.1.  Client info . . . . . . . . . . . . . . . . . . . . .   7
       4.4.2.  Double-spend protection . . . . . . . . . . . . . . .   7
     4.5.  Handling errors . . . . . . . . . . . . . . . . . . . . .   7
   5.  Functionality . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Data structures . . . . . . . . . . . . . . . . . . . . .   8
       5.1.1.  Ciphersuite . . . . . . . . . . . . . . . . . . . . .   8
       5.1.2.  Keys  . . . . . . . . . . . . . . . . . . . . . . . .   8
       5.1.3.  IssuanceInput . . . . . . . . . . . . . . . . . . . .   8
       5.1.4.  IssuanceResponse  . . . . . . . . . . . . . . . . . .   9
       5.1.5.  RedemptionToken . . . . . . . . . . . . . . . . . . .   9
       5.1.6.  RedemptionRequest . . . . . . . . . . . . . . . . . .   9
       5.1.7.  RedemptionResponse  . . . . . . . . . . . . . . . . .  10
     5.2.  API functions . . . . . . . . . . . . . . . . . . . . . .  10
       5.2.1.  Generate  . . . . . . . . . . . . . . . . . . . . . .  10
       5.2.2.  Issue . . . . . . . . . . . . . . . . . . . . . . . .  10
       5.2.3.  Process . . . . . . . . . . . . . . . . . . . . . . .  11
       5.2.4.  Redeem  . . . . . . . . . . . . . . . . . . . . . . .  11
       5.2.5.  Verify  . . . . . . . . . . . . . . . . . . . . . . .  11
     5.3.  Error types . . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Security considerations . . . . . . . . . . . . . . . . . . .  12
     6.1.  Unlinkability . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  One-more unforgeability . . . . . . . . . . . . . . . . .  13
     6.3.  Double-spend protection . . . . . . . . . . . . . . . . .  14
     6.4.  Additional token metadata . . . . . . . . . . . . . . . .  14
     6.5.  Maximum number of tokens issued . . . . . . . . . . . . .  14
   7.  VOPRF instantiation . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  Recommended ciphersuites  . . . . . . . . . . . . . . . .  15
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