The Privacy Pass Protocol
draft-privacy-pass-00

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Network Working Group                                        A. Davidson
Internet-Draft                                       Cloudflare Portugal
Intended status: Informational                               N. Sullivan
Expires: May 6, 2020                                          Cloudflare
                                                       November 03, 2019

                       The Privacy Pass Protocol
                         draft-privacy-pass-00

Abstract

   This document specifies the Privacy Pass protocol for anonymously
   authorizing clients with services on the Internet.

Note to Readers

   Source for this draft and an issue tracker can be found at
   https://github.com/grittygrease/draft-privacy-pass [1].

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 May 6, 2020.

Copyright Notice

   Copyright (c) 2019 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 and restrictions with respect
   to this document.  Code Components extracted from this document must

Davidson & Sullivan        Expires May 6, 2020                  [Page 1]
Internet-Draft                 PP protocol                 November 2019

   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 . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Preliminaries . . . . . . . . . . . . . . . . . . . . . .   4
       1.2.1.  Elliptic curve points . . . . . . . . . . . . . . . .   4
       1.2.2.  Protocol messages . . . . . . . . . . . . . . . . . .   4
     1.3.  Layout  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.4.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Generalized protocol overview . . . . . . . . . . . . . . . .   5
     2.1.  Key initialisation phase  . . . . . . . . . . . . . . . .   6
     2.2.  Issuance phase  . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  Redemption phase  . . . . . . . . . . . . . . . . . . . .   9
       2.3.1.  Double-spend protection . . . . . . . . . . . . . . .  10
       2.3.2.  Finalization during redemption  . . . . . . . . . . .  11
     2.4.  Error types . . . . . . . . . . . . . . . . . . . . . . .  11
   3.  Key registration  . . . . . . . . . . . . . . . . . . . . . .  11
     3.1.  Key rotation  . . . . . . . . . . . . . . . . . . . . . .  12
     3.2.  Client retrieval  . . . . . . . . . . . . . . . . . . . .  13
     3.3.  Key revocation  . . . . . . . . . . . . . . . . . . . . .  14
     3.4.  VOPRF ciphersuites  . . . . . . . . . . . . . . . . . . .  14
     3.5.  ECDSA key material  . . . . . . . . . . . . . . . . . . .  15
   4.  Protocol configurations . . . . . . . . . . . . . . . . . . .  15
     4.1.  Single-Issuer Single-Verifier . . . . . . . . . . . . . .  15
     4.2.  Single-Issuer Forwarding-Verifier . . . . . . . . . . . .  16
     4.3.  Single-Issue Asynchronous-Verifier  . . . . . . . . . . .  16
     4.4.  Bounded-Issuers . . . . . . . . . . . . . . . . . . . . .  17
       4.4.1.  Fixing the bound  . . . . . . . . . . . . . . . . . .  17
   5.  Privacy considerations  . . . . . . . . . . . . . . . . . . .  17
     5.1.  User segregation  . . . . . . . . . . . . . . . . . . . .  18
       5.1.1.  Key rotation  . . . . . . . . . . . . . . . . . . . .  18
       5.1.2.  Large numbers of issuers  . . . . . . . . . . . . . .  18
     5.2.  Tracking and identity leakage . . . . . . . . . . . . . .  20
   6.  Security considerations . . . . . . . . . . . . . . . . . . .  20
     6.1.  Double-spend protection . . . . . . . . . . . . . . . . .  20
     6.2.  Key rotation  . . . . . . . . . . . . . . . . . . . . . .  20
     6.3.  Token exhaustion  . . . . . . . . . . . . . . . . . . . .  21
   7.  Summary of privacy and security parameters  . . . . . . . . .  21
     7.1.  Justification . . . . . . . . . . . . . . . . . . . . . .  22