Internet-Draft HTTP Privacy Token September 2021
Pauly, et al. Expires 11 March 2022 [Page]
Network Working Group
Intended Status:
T. Pauly
Apple Inc.
F. Jacobs
Apple Inc.
C.A. Wood

The Privacy Token HTTP Authentication Scheme


This documents defines an authentication scheme for HTTP called Privacy Token.

Discussion Venues

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This Internet-Draft will expire on 11 March 2022.

Table of Contents

1. Introduction

This document defines a new HTTP authentication scheme [RFC7235] named "PrivacyToken".

This scheme is built to be used to authenticate to proxies, using the Proxy-Authorization header field, with a blind signature that allows a proxy to verify that a client has a token signed by a particular key, but without identifying the client. The initial version of this scheme is intended to be used with RSA Blind Signatures [RSASIG].

1.1. Requirements

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.

2. Privacy Token Structure

A privacy token is a structure that begins with a single byte that indicates a version. This document defines version, 1, which indicates use of private tokens based on RSA Blind Signatures [RSASIG], and determines the rest of the structure contents.

struct {
    uint8_t version;
    uint8_t key_id[32];
    uint8_t message[32];
    uint8_t signature[Nk];
} Token;

The structure fields are defined as follows:

3. PrivacyToken Authentication Scheme

The "PrivacyToken" authentication scheme defines one parameter, "token". All unknown or unsupported parameters to "PrivacyToken" authentication credentials MUST be ignored.

The value of the "token" parameter is a Privacy Token Structure Section 2, encoded using base64url encoding [RFC4648].

As an example, a Proxy-Authorization field in an HTTP request would look like:

Proxy-Authorization: PrivacyToken token=abc...

4. Security Considerations

Note that the KeyID is only a hint to identify the public verification key. With a sufficiently large number of public keys, KeyID collisions may occur. By approximation, a KeyID collision between two distinct keys will occur with probability sqrt(p * 2^33). In such cases, servers SHOULD attempt verification using both keys.

5. IANA Considerations

This document registers the "PrivacyToken" authentication scheme in the "Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry" established by [RFC7235].

Authentication Scheme Name: PrivacyToken

Pointer to specification text: Section 3 of this document

6. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, , <>.
Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Authentication", RFC 7235, DOI 10.17487/RFC7235, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Denis, F., Jacobs, F., and C. A. Wood, "RSA Blind Signatures", Work in Progress, Internet-Draft, draft-irtf-cfrg-rsa-blind-signatures-02, , <>.

Authors' Addresses

Tommy Pauly
Apple Inc.
One Apple Park Way
Cupertino, California 95014,
United States of America
Frederic Jacobs
Apple Inc.
One Apple Park Way
Cupertino, California 95014,
United States of America
Christopher A. Wood