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draft-privacy-token.md

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title: The Privacy Token HTTP Authentication Scheme abbrev: HTTP Privacy Token docname: draft-privacy-token-latest category: exp

ipr: trust200902 keyword: Internet-Draft

stand_alone: yes pi: [toc, sortrefs, symrefs]

author:

ins: T. Pauly
name: Tommy Pauly
org: Apple Inc.
street: One Apple Park Way
city: Cupertino, California 95014
country: United States of America
email: [email protected]
  • ins: F. Jacobs name: Frederic Jacobs org: Apple Inc. street: One Apple Park Way city: Cupertino, California 95014 country: United States of America email: [email protected]
  • ins: C. A. Wood name: Christopher A. Wood org: Cloudflare email: [email protected]

--- abstract

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

--- middle

Introduction {#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=I-D.irtf-cfrg-rsa-blind-signatures}}.

Requirements

{::boilerplate bcp14}

Privacy Token Structure {#struct}

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:

  • "version" is a 1-octet integer. This document defines version 1.

  • "key_id" is a collision-resistant hash that identifies the key used to produce the signature. This is generated as SHA256(public_key), where public_key is a DER-encoded SubjectPublicKeyInfo object carrying the public key.

  • "message" is a 32-octet random message that is signed by the signature.

  • "signature" is a Nk-octet RSA Blind Signature that covers the message. For version 1, Nk is indicated by size of the Token structure and may be 256, 384, or 512. These correspond to RSA 2048, 3072, and 4096 bit keys. Clients implementing version 1 MUST support signature sizes with Nk of 512 and 256.

PrivacyToken Authentication Scheme {#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 {{struct}}, encoded using base64url encoding {{!RFC4648}}.

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

Proxy-Authorization: PrivacyToken token=abc...

Security Considerations {#security}

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.

IANA Considerations {#iana}

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: {{scheme}} of this document