Privacy Pass: Architectural Framework
draft-davidson-pp-architecture-01
Network Working Group A. Davidson
Internet-Draft Cloudflare Portugal
Intended status: Informational 13 July 2020
Expires: 14 January 2021
Privacy Pass: Architectural Framework
draft-davidson-pp-architecture-01
Abstract
This document specifies the architectural framework for constructing
secure and anonymity-preserving instantiations of the Privacy Pass
protocol. It provides recommendations on how the protocol ecosystem
should be constructed to ensure the privacy of clients, and the
security of all participating entities.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 14 January 2021.
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Davidson Expires 14 January 2021 [Page 1]
Internet-Draft PP architecture July 2020
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Ecosystem participants . . . . . . . . . . . . . . . . . . . 4
3.1. Servers . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. Client identifying information . . . . . . . . . . . 6
4. Key management framework . . . . . . . . . . . . . . . . . . 6
4.1. Public key registries . . . . . . . . . . . . . . . . . . 7
4.2. Key rotation . . . . . . . . . . . . . . . . . . . . . . 8
4.3. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . 8
5. Server running modes . . . . . . . . . . . . . . . . . . . . 9
5.1. Single-Verifier . . . . . . . . . . . . . . . . . . . . . 9
5.2. Delegated-Verifier . . . . . . . . . . . . . . . . . . . 9
5.3. Asynchronous-Verifier . . . . . . . . . . . . . . . . . . 10
5.4. Public-Verifier . . . . . . . . . . . . . . . . . . . . . 10
5.5. Bounded number of servers . . . . . . . . . . . . . . . . 10
6. Client-Server trust relationship . . . . . . . . . . . . . . 11
7. Privacy considerations . . . . . . . . . . . . . . . . . . . 12
7.1. Server key rotation . . . . . . . . . . . . . . . . . . . 12
7.2. Large numbers of servers . . . . . . . . . . . . . . . . 13
7.2.1. Allowing larger number of servers . . . . . . . . . . 13
7.3. Partitioning of server key material . . . . . . . . . . . 14
7.4. Additional token metadata . . . . . . . . . . . . . . . . 14
7.5. Tracking and identity leakage . . . . . . . . . . . . . . 15
7.6. Client incentives for anonymity reduction . . . . . . . . 15
8. Security considerations . . . . . . . . . . . . . . . . . . . 15
8.1. Double-spend protection . . . . . . . . . . . . . . . . . 16
8.2. Token exhaustion . . . . . . . . . . . . . . . . . . . . 16
8.3. Avoiding server centralization . . . . . . . . . . . . . 16
9. Protocol parametrization . . . . . . . . . . . . . . . . . . 16
9.1. Justification . . . . . . . . . . . . . . . . . . . . . . 17
9.2. Example parameterization . . . . . . . . . . . . . . . . 18
9.3. Allowing more servers . . . . . . . . . . . . . . . . . . 19
10. Extension integration policy . . . . . . . . . . . . . . . . 19
11. Existing applications . . . . . . . . . . . . . . . . . . . . 19
11.1. Cloudflare challenge pages . . . . . . . . . . . . . . . 19
11.2. Trust Token API . . . . . . . . . . . . . . . . . . . . 20
11.3. Zero-knowledge Access Passes . . . . . . . . . . . . . . 20
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