Internet-Draft Privacy Pass Geolocation Hint Extension July 2023
Hendrickson & Wood Expires 11 January 2024 [Page]
Privacy Pass
Intended Status:
S. Hendrickson
C. A. Wood
Cloudflare, Inc.

Privacy Pass Geolocation Hint Extension


This document describes an extension for Privacy Pass that allows tokens to encode geolocation hints.

About This Document

This note is to be removed before publishing as an RFC.

The latest revision of this draft can be found at Status information for this document may be found at

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Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on 11 January 2024.

Table of Contents

1. Introduction

Some Privacy Pass token types support binding additional information to the tokens, often referred to as public metadata. [AUTH-EXTENSIONS] describes an extension parameter to the basic PrivateToken HTTP authentication scheme [AUTH-SCHEME] for supplying this metadata alongside a token. [EXTENDED-ISSUANCE] describes variants of the basic Privacy Pass issuance protocols [BASIC-ISSUANCE] that support issuing tokens with public metadata. However, there are no existing extensions defined to make use of these protocol extensions.

This document describes an extension for Privacy Pass that allows tokens to encode geolocation hints. These hints can be used by origins that redeem tokens to influence its behavior in various ways, such as determining the content of HTTP responses.

2. Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Geolocation Hint Extension

The geolocation hint extension is an extension used to convey rough geolocation hints to origins that do not already have accurate or authoritative mappings for the IP addresses of clients. This can be particularly useful for cases where IP geolocation mappings have changed recently, or a client is using a VPN or proxy that may not be commonly recognized by servers.

The value of this extension is an GeoHintTimestamp, defined as follows.

struct {
   opaque geo_hint<1..2^16-1>;
} GeoHint;

The GeoHintTimestamp fields are defined as follows:

As an example, a GeoHint structure corresponding to the ",US,US-AL,Alabaster" entry would be:

struct {
   opaque geo_hint<1..2^16-1>; // "US,US-AL,Alabaster"
} GeoHint;

4. Security Considerations

Geolocation information can contribute to a client's fingerprint. Exposing precise geolocation information can therefore lead to anonymity set partitioning, as described in [ARCHITECTURE]. More general information regarding the use of extensions and their possible impact on client privacy can be found in [ARCHITECTURE].

Servers MUST NOT use IP Geolocation Client Hints for making security or access-control decisions, as the value can be spoofed by a client. The hint is intended only for use in optimizing behavior.

5. IANA Considerations

This document registers the following entry into the "Privacy Pass PrivateToken Extensions" registry.

6. Normative References

Davidson, A., Iyengar, J., and C. A. Wood, "The Privacy Pass Architecture", Work in Progress, Internet-Draft, draft-ietf-privacypass-architecture-13, , <>.
Hendrickson, S. and C. A. Wood, "The PrivateToken HTTP Authentication Scheme Extensions Parameter", Work in Progress, Internet-Draft, draft-wood-privacypass-auth-scheme-extensions-00, , <>.
Pauly, T., Valdez, S., and C. A. Wood, "The Privacy Pass HTTP Authentication Scheme", Work in Progress, Internet-Draft, draft-ietf-privacypass-auth-scheme-11, , <>.
Celi, S., Davidson, A., Valdez, S., and C. A. Wood, "Privacy Pass Issuance Protocol", Work in Progress, Internet-Draft, draft-ietf-privacypass-protocol-11, , <>.
Kline, E., Duleba, K., Szamonek, Z., Moser, S., and W. Kumari, "A Format for Self-Published IP Geolocation Feeds", RFC 8805, DOI 10.17487/RFC8805, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.


This document received input and feedback from Jim Laskey.

Authors' Addresses

Scott Hendrickson
Christopher A. Wood
Cloudflare, Inc.