Privacy Pass Architectural Framework
draft-ietf-privacypass-architecture-01
Network Working Group A. Davidson
Internet-Draft LIP
Intended status: Informational C.A. Wood
Expires: 23 August 2021 Cloudflare
19 February 2021
Privacy Pass Architectural Framework
draft-ietf-privacypass-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 23 August 2021.
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Copyright (c) 2021 IETF Trust and the persons identified as the
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Davidson & Wood Expires 23 August 2021 [Page 1]
Internet-Draft PP architecture February 2021
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 and discovery . . . . . . . . . . . . . . . . 6
4.1. Key rotation . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . 8
5. Server running modes . . . . . . . . . . . . . . . . . . . . 8
5.1. Single-Verifier . . . . . . . . . . . . . . . . . . . . . 8
5.2. Delegated-Verifier . . . . . . . . . . . . . . . . . . . 8
5.3. Asynchronous-Verifier . . . . . . . . . . . . . . . . . . 9
5.4. Public-Verifier . . . . . . . . . . . . . . . . . . . . . 9
5.5. Bounded number of servers . . . . . . . . . . . . . . . . 10
6. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Client privacy implications . . . . . . . . . . . . . . . 11
7. Client-Server trust relationship . . . . . . . . . . . . . . 11
8. Privacy considerations . . . . . . . . . . . . . . . . . . . 12
8.1. Server key rotation . . . . . . . . . . . . . . . . . . . 12
8.2. Large numbers of servers . . . . . . . . . . . . . . . . 13
8.2.1. Allowing larger number of servers . . . . . . . . . . 14
8.3. Partitioning of server key material . . . . . . . . . . . 14
8.4. Tracking and identity leakage . . . . . . . . . . . . . . 15
8.5. Client incentives for anonymity reduction . . . . . . . . 15
9. Security considerations . . . . . . . . . . . . . . . . . . . 15
9.1. Double-spend protection . . . . . . . . . . . . . . . . . 16
9.2. Token exhaustion . . . . . . . . . . . . . . . . . . . . 16
9.3. Avoiding server centralization . . . . . . . . . . . . . 16
10. Protocol parametrization . . . . . . . . . . . . . . . . . . 16
10.1. Justification . . . . . . . . . . . . . . . . . . . . . 17
10.2. Example parameterization . . . . . . . . . . . . . . . . 18
10.3. Allowing more servers . . . . . . . . . . . . . . . . . 19
11. Extension integration policy . . . . . . . . . . . . . . . . 19
12. Existing applications . . . . . . . . . . . . . . . . . . . . 19
12.1. Cloudflare challenge pages . . . . . . . . . . . . . . . 19
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