]> The PrivateToken HTTP Authentication Scheme Extensions Parameter Google
scott@shendrickson.com
Cloudflare, Inc.
caw@heapingbits.net
Security Privacy Pass token This document specifies a new parameter for the "PrivateToken" HTTP authentication scheme. This purpose of this parameter is to carry extensions for Privacy Pass protocols that support public metadata. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Privacy Pass Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .
Introduction The primary Token structure in the "PrivateToken" HTTP authentication scheme is composed as follows: Functionally, this structure conveys a single bit of information from the issuance protocol: whether or not the token is valid (as indicated by a valid authenticator value). This structure does not admit any additional information to flow from the issuance protocol, including, for example, public metadata that is incorporated into the issuance protocol. This document specifies a new parameter for the "PrivateToken" HTTP authentication scheme for carrying extensions. This extensions parameter, otherwise referred to as public metadata, is cryptographically bound to the Token structure via the Privacy Pass issuance protocol.
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 when, and only when, they appear in all capitals, as shown here.
PrivateToken Extensions Parameter As defined in , the "PrivateToken" authentication scheme defines one parameter, "token", which contains the base64url-encoded Token struct. This document defines a new parameter, "extensions," which contains the base64url-encoded representation of the following Extensions structure. ; } Extension; enum { reserved(0), (65535) } ExtensionType; struct { Extension extensions<0..2^16-1>; } Extensions; ]]> The contents of Extensions are a list of Extension values, each of which is a type-length-value structure whose semantics are determined by the type. The type and length of each extension are 2-octet integers, in network byte order. The length of the extensions list is also a is a 2-octet integer, in network byte order. Clients, Issuers, and Origins all agree on the content and encoding of this Extensions structure, i.e., they agree on the same type-length-value list. The list MUST be ordered by ExtensionType value, from 1 to 65535. The value of the Extensions structure is used as-is when verifying the value of the corresponding "token" parameter in the "PrivateToken" authentication header. Future documents may specify extensions to be included in this structure. Registration details for these extensions are in . Each Privacy Pass issuance protocol, identified by a token type, specifices the structure of the PrivateToken value to be used. Issuance protocols that support public metadata would define a way to convey this metadata as a set of extensions in an Extensions structure.
Security Considerations Privacy considerations for tokens that include additional information are discussed in .
IANA Considerations IANA is requested to create a new "Privacy Pass PrivateToken Extensions" registry in the "Privacy Pass Parameters" page to list possible extension values and their meaning. Each extension has a two-byte type, so the maximum possible value is 0xFFFF = 65535. Template:
  • Type: The two-byte extension type
  • Name: Name of the extension
  • Value: Syntax and semantics of the extension
  • Reference: Where this extension and its value are defined
  • Notes: Any notes associated with the entry
New entries in this registry are subject to the Specification Required registration policy (). Designated experts need to ensure that the extension is sufficiently clearly defined and, importantly, has a clear description about the privacy implications of using the extension framed in the context of partitioning the client anonymity set as described in . Values 0xF000-0xFFFF are reserved for private use, to enable proprietary uses and limited experimentation.
References Normative References The Privacy Pass HTTP Authentication Scheme Apple Inc. Google LLC Cloudflare This document defines an HTTP authentication scheme that can be used by clients to redeem Privacy Pass tokens with an origin. It can also be used by origins to challenge clients to present an acceptable Privacy Pass token. Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Guidelines for Writing an IANA Considerations Section in RFCs Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. Informative References The Privacy Pass Architecture LIP Fastly Cloudflare This document specifies the Privacy Pass architecture and requirements for its constituent protocols used for constructing privacy-preserving authentication mechanisms. It provides recommendations on how the architecture should be deployed to ensure the privacy of clients and the security of all participating entities.