Privacy Pass: Centralization Problem Statement
draft-mcfadden-pp-centralization-problem-00

Document Type Active Internet-Draft (individual)
Author Mark McFadden 
Last updated 2020-11-02
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Privacy Pass                                                M. McFadden
Internet Draft                            internet policy advisors, llc
Intended status: Informational                         November 2, 2020
Expires: May 2, 2021

              Privacy Pass: Centralization Problem Statement
              draft-mcfadden-pp-centralization-problem-00.txt

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on May 2, 2021.

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Abstract

   This document discusses the problems and mitigations associated with
   strict upper bounds on the number of Privacy Pass servers in the
   proposed Privacy Pass ecosystem. It documents a proposed problem
   statement.

Table of Contents

   1. Introduction...................................................2
   2. Potential Privacy Concerns.....................................3
   3. Centralization in Privacy Pass - Problem Statement.............4
      3.1. Architectural Problems....................................4
      3.2. Engineering Problems......................................5
      3.3. Practical Problems........................................6
   4. Problem Statement and Potential for Mitigations................6
      4.1. Problem Statement.........................................6
      4.2. Potential Mitigations.....................................6
   5. Security Considerations........................................7
   6. IANA Considerations............................................7
   7. References.....................................................7
      7.1. Informative References....................................7
   8. Acknowledgments................................................7

1. Introduction

   The Privacy Pass protocol provides a set of cross-domain
   authorization tokens that protect the client's anonymity in message
   exchanges with a server.  This allows clients to communicate an
   attestation of a previously authenticated server action, without
   having to reauthenticate with user intervention.  The tokens retain
   anonymity when this is defined as the act of revealing them cannot
   be linked back to the session where they were initially issued.

   The protocol itself in defined in [1] and the architectural
   framework is in [2].

   The architecture document leaves for a later time the issue of
   server centralization.  This document is a discussion of the
   problems related to server centralization in Privacy Pass, the
   impact of centralization on the protocol's privacy goals, and some
   potential mitigations for the problem.

   An important feature of the Privacy Pass Architecture is the concept
   of the anonymity set of each individual client. The Privacy Pass

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   ecosystem has a set of servers which issue tokens to clients which
   can then be redeemed at the application layer for authentication.

   Trust is an important component in Privacy Pass. The servers have to
   publish their public keys and details of the ciphersuite they are
   using. It is necessary to publish these in a globally consistent,
   tamper-proof data structure. Clients that use the same registry of
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