Internet DRAFT - draft-jmiller-jose-json-proof-token
draft-jmiller-jose-json-proof-token
jose J. Miller
Internet-Draft Ping Identity
Intended status: Standards Track M. Jones
Expires: 11 September 2023 Microsoft
10 March 2023
JSON Proof Token
draft-jmiller-jose-json-proof-token-01
Abstract
JSON Proof Token (JPT) is a compact, URL-safe, privacy-preserving
representation of claims to be transferred between three parties.
The claims in a JPT are encoded as base64url-encoded JSON objects
that are used as the payloads of a JSON Web Proof (JWP)
(https://www.ietf.org/archive/id/draft-jmiller-jose-json-web-proof-
01.html) structure, enabling them to be digitally signed and
selectively disclosed. JPTs also support reusability and
unlinkability when using Zero-Knowledge Proofs (ZKPs).
Status of This Memo
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This Internet-Draft will expire on 11 September 2023.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Design Considerations . . . . . . . . . . . . . . . . . . . . 3
4.1. Unlinkability . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Selective Disclosure . . . . . . . . . . . . . . . . . . 4
4.3. Familiarity . . . . . . . . . . . . . . . . . . . . . . . 4
4.4. Proofs . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Claim Names . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Payloads . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Disclosed . . . . . . . . . . . . . . . . . . . . . . . . 6
7.2. Proof Methods . . . . . . . . . . . . . . . . . . . . . . 6
8. Example JPT . . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
11. Informative References . . . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7
Appendix B. Document History . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
JSON Proof Token (JPT) is a compact claims representation format
intended to be used in the same ways as a JSON Web Token (JWT), but
with additional support for selective disclosure and unlinkability.
JPTs encode claim values to be transmitted as payloads of a JSON Web
Proof (JWP) (https://www.ietf.org/archive/id/draft-jmiller-jose-json-
web-proof-01.html). JPTs are always represented using the JWP
Compact Serialization. The corresponding claim names are not
transmitted in the payloads and are stored in a separate structure
that can be externalized and shared across multiple JPTs.
| Editor's Note: This draft is still early and incomplete, there
| will be significant changes to the algorithms as currently defined
| here. Please do not use any of these definitions or examples for
| anything except personal experimentation and learning.
| Contributions and feedback are welcome at https://github.com/json-
| web-proofs/json-web-proofs (https://github.com/json-web-proofs/
| json-web-proofs).
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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. Background
JWP defines a container binding together a protected header, one or
more payloads, and a cryptographic proof. It does not define how
claims are organized into payloads and what formats they are in.
JPTs are intended to be as close to a JWT as possible, while also
supporting the selective disclosure and unlinkability of JWPs.
4. Design Considerations
The rationale behind the design for JSON Proof Tokens is important
when considering how it is structured. These sections detail the
underlying reasoning for the approach defined by JPTs.
4.1. Unlinkability
Supporting unlinkability is perhaps the most challenging design
constraint for JPTs. Even the smallest oversight can introduce a
subtle vector for relying parties to collude and correlate one or
more subjects across their usage.
The principal tools to prevent this are data minimization and
uniformity. The data included in a JPT SHOULD be minimized to remove
potential correlation points. The data SHOULD contain only values
that are able to be selectively disclosed with consent or transformed
by the proof algorithm when presented.
Any other data that is repeated across multiple JPTs is externalized
so that it is uniform across every issuance. This includes
preventing the usage of optional headers, dynamic mapping of claims
to payloads, changes to how many payloads are included, and the
ordering of the payloads.
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4.2. Selective Disclosure
While JWPs provide the underling structure for easily supporting
selective disclosure, JPTs must go a step further to ensure that
applications can effectively provide choice and consent on exactly
what is being disclosed. Software using JWPs must know the mappings
from payloads to claims. JPTs do not support disclosing claims that
are intended to be private from the issuer to the relying party. All
disclosed payloads MUST be mapped to claims and made accessible to
the application.
4.3. Familiarity
JPTs are intended to be as close to a JWT as possible in order to
provide the simplest transition for any JWT-based system to add
support for a JPT.
Although there are some stark differences in the lifecycle of a JPT,
from the application's perspective, the interface to a JPT can be
made fairly similar: a JSON object containing a mix of required and
optional claims with well-understood values.
The most significant divergence required by JPTs is that of
supporting values that may be disclosed or may instead only be a
proof about the value. Applications are required to interact with
the JPT on a payload-by-payload basis instead of just verifying a JWT
and then being able to interact with the JSON body directly.
4.4. Proofs
In order to generate a variety of efficient ZKPs of knowledge, range,
membership, or other predicates, it is essential that each individual
payload is only a single claim value. This greatly simplifies the
task of linking a derived proof of a given claim to the specific
payload that was also signed by the issuer. While JPTs support
claims that have complex object or array compound values, they also
allow for simple claim values such as JSON strings, numbers, and
booleans that can be used directly in generating predicate proofs.
5. Claim Names
It is suggested that the claim names used with JPTs come from those
in the IANA JSON Web Token Claims Registry, when those fit the
application's needs.
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6. Claims
Using a JSON Proof Token requires combining information from two
sources: the claim names and the payloads. The simplest solution is
to list the claim names in an ordered array that aligns with the
included payloads. This claims array can be conveniently included in
the JWP Protected Header using the claims key.
When the claims array is stored in the header, any variations of it
are disclosed to the verifier and can be used to correlate and link
usages. Given the privacy design considerations around linkability
it is recommended that the claims are defined external to an
individual JPT and either referenced or known by the application
context.
In order to facilitate this external definition of the claim names,
an additional cid key is defined with a required digest value
calculated as defined here. This cid can be used similar to a kid in
order to ensure externally resolve and then verify that the correct
list of claim names is being used when processing the payloads
containing the claim values.
If there is an associated JWK containing the signing key information,
the claims key is also registered there as a convenient location for
the claim names.
All payloads are claim values and MUST be the base64url encoding of
the UTF-8 representation of a JSON value.
The following is an example JWP Protected Header that includes a
claims array:
{
"kid": "HjfcpyjuZQ-O8Ye2hQnNbT9RbbnrobptdnExR0DUjU8",
"alg": "BBS",
"claims": [
"iat",
"exp",
"family_name",
"given_name",
"email"
]
}
7. Payloads
| Editor's Note: This section is significantly incomplete, use it
| only as an indicator of the intended direction.
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Application resolves each claim as required when processing the JPT.
Resolution can result in one of three things: 1. A disclosed JSON
value 2. A custom proof method 3. A null value
7.1. Disclosed
Always an octet string of valid JSON text.
7.2. Proof Methods
* proof methods can be returned instead of a disclosed payload
* these are generated by the algorithm from information in the JWP's
proof value
* a proof method may be custom based on the capabilities of the
algorithm
* define common proof method types available?
- range
- membership
- time
- knowledge
- linking
8. Example JPT
See the JSON Web Proof draft appendix.
9. Security Considerations
* Protected Header Minimization
10. IANA Considerations
This document has no IANA actions.
11. Informative 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>.
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[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>.
Appendix A. Acknowledgements
TBD
Appendix B. Document History
[[ To be removed from the final specification ]]
-01
* Applied editorial improvements
-00
* First individual draft targeting JOSE working group
Authors' Addresses
Jeremie Miller
Ping Identity
Email: jmiller@pingidentity.com
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: https://self-issued.info/
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