The Privacy Token HTTP Authentication Scheme
draft-privacy-token-00

Network Working Group                                           T. Pauly
Internet-Draft                                                 F. Jacobs
Intended status: Experimental                                 Apple Inc.
Expires: 9 September 2021                                      C.A. Wood
                                                              Cloudflare
                                                            8 March 2021

              The Privacy Token HTTP Authentication Scheme
                         draft-privacy-token-00

Abstract

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

Discussion Venues

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

   Source for this draft and an issue tracker can be found at
   https://github.com/tfpauly/privacy-proxy.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 9 September 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.

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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Privacy Token Structure . . . . . . . . . . . . . . . . . . .   2
   3.  PrivacyToken Authentication Scheme  . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

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.

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   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 512.

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.

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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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235,
              DOI 10.17487/RFC7235, June 2014,
              <https://www.rfc-editor.org/info/rfc7235>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RSASIG]   "RSA Blind Signatures", March 2020,
              <https://tools.ietf.org/html/draft-wood-cfrg-rsa-blind-
              signatures-00>.

Authors' Addresses

   Tommy Pauly
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014,
   United States of America

   Email: tpauly@apple.com

   Frederic Jacobs
   Apple Inc.
   One Apple Park Way

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   Cupertino, California 95014,
   United States of America

   Email: frederic.jacobs@apple.com

   Christopher A. Wood
   Cloudflare

   Email: caw@heapingbits.net

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