jose M. Jones
Internet-Draft Self-Issued Consulting
Intended status: Standards Track D. Waite
Expires: 18 September 2025 J. Miller
Ping Identity
17 March 2025
JSON Proof Token and CBOR Proof Token
draft-ietf-jose-json-proof-token-08
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) structure,
enabling them to be digitally signed and selectively disclosed. JPTs
also support reusability and unlinkability when using Zero-Knowledge
Proofs (ZKPs).
A CBOR-based representation of JPTs is also defined, called a CBOR
Proof Token (CPT). It has the same properties of JPTs, but uses the
JSON Web Proof (JWP) CBOR Serialization, rather than the JSON-based
JWP Compact Serialization.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 18 September 2025.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
Jones, et al. Expires 18 September 2025 [Page 1]
Internet-Draft json-proof-token March 2025
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.
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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Design Considerations . . . . . . . . . . . . . . . . . . . . 3
4.1. Unlinkability . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Selective Disclosure . . . . . . . . . . . . . . . . . . 4
4.3. Familiarity . . . . . . . . . . . . . . . . . . . . . . . 4
4.4. Proofs . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Claim Names . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Claims Header Parameter . . . . . . . . . . . . . . . . . . . 5
7. Claims ID ("cid") JWP Header Parameter . . . . . . . . . . . 6
8. Presented Claims and Proofs . . . . . . . . . . . . . . . . . 7
8.1. Disclosed . . . . . . . . . . . . . . . . . . . . . . . . 7
8.2. Undisclosed . . . . . . . . . . . . . . . . . . . . . . . 7
8.3. Proof Methods . . . . . . . . . . . . . . . . . . . . . . 7
9. Example JPTs . . . . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11.1. JSON Web Proof Header Parameters Registration . . . . . 8
11.1.1. Registry Contents . . . . . . . . . . . . . . . . . 8
11.1.1.1. "claims" (Claims) Header Parameter . . . . . . . 8
11.1.1.2. "cid" (Claims ID) Header Parameter . . . . . . . 8
11.2. JSON Web Key Parameters Registry . . . . . . . . . . . . 8
11.2.1. Registry Contents . . . . . . . . . . . . . . . . . 8
11.3. COSE Key Common Parameters Registry . . . . . . . . . . 9
11.3.1. Registry Contents . . . . . . . . . . . . . . . . . 9
11.4. Media Types Registry . . . . . . . . . . . . . . . . . . 9
11.4.1. application/jpt . . . . . . . . . . . . . . . . . . 9
11.4.2. application/cpt . . . . . . . . . . . . . . . . . . 10
11.5. CoAP Content-Formats Registry . . . . . . . . . . . . . 10
11.5.1. "CPT" CoAP Content-Format . . . . . . . . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 11
12.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12
Appendix B. Document History . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
Jones, et al. Expires 18 September 2025 [Page 2]
Internet-Draft json-proof-token March 2025
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)
[RFC7519], but with additional support for selective disclosure and
unlinkability. JPTs encode claim values to be transmitted as
payloads of a JSON Web Proof (JWP) [I-D.ietf-jose-json-web-proof].
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.
Likewise, CBOR Proof Token (CPT) is a similar compact claims
representation format intended to be used in the same ways as a CBOR
Web Token (CWT) [RFC8392], but with the same support for selective
disclosure and unlinkability. CPTs are represented using the JWP
CBOR 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 CPTs.
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.
Likewise, CPTs are intended to be as close to a CWT as possible,
while also supporting the selective disclosure and unlinkability of
JWPs.
4. Design Considerations
The rationale behind the design for JSON Proof Tokens and CBOR Proof
Tokens is important when considering how they are structured. These
sections detail the underlying reasoning informing their design.
Jones, et al. Expires 18 September 2025 [Page 3]
Internet-Draft json-proof-token March 2025
4.1. Unlinkability
Supporting unlinkability is perhaps the most challenging design
constraint for JPTs and CPTs. 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 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 or CPTs 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.
4.2. Selective Disclosure
While JWPs provide the underling structure for easily supporting
selective disclosure, JPTs and CPTs must go a step further to ensure
that holders can effectively provide choice and consent on exactly
what is being disclosed. Software using JWPs or CPTs MUST know the
mappings from payloads to claims. All disclosed payloads MUST be
mapped to claims and made accessible to the application. Holders
SHOULD understand the semantics of all potentially disclosed claims
to the extent needed to decide whether to disclose them. JPTs and
CPTs SHOULD NOT contain claims that are intended only for a specific
verifier.
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 JPTs. The same is true for CPTs and CWTs.
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. Likewise, A CPT is a
CBOR object containing a mix of required and optional claims with
well-understood values.
The most significant divergence required by JPTs and CPTs 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
Jones, et al. Expires 18 September 2025 [Page 4]
Internet-Draft json-proof-token March 2025
the JPT or CPT on a payload-by-payload basis instead of just
verifying a JWT or CWT and then being able to interact with the JSON
or CBOR body directly.
4.4. Proofs
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 and CPTs
support claims that have complex object or array compound values,
they also allow for simple claim values such as strings, numbers, and
booleans that can be used directly in generating predicate proofs.
5. Claim Names
It is RECOMMENDED that the claim names used with JPTs come from those
in the IANA JSON Web Token Claims Registry [IANA.JWT] established by
[RFC7519], when those fit the application's needs. Likewise, it is
RECOMMENDED that the claim names used with CPTs come from those in
the IANA CBOR Web Token Claims Registry [IANA.CWT] established by
[RFC8392], when those fit the application's needs.
6. Claims Header Parameter
A JSON Proof Token or CBOR Proof Token assigns each playload a claim
name. Payloads MUST each have a negotiated and understood claim name
within the application context. The simplest solution to establish
payload claim names is as an ordered array that aligns with the
included payloads. This claims array can be conveniently included in
the Claims header parameter.
The claims Header Parameter is an array listing the Claim Names
corresponding to the JWP payloads, in the same order as the payloads.
Each array value is a Claim Name, as defined in [RFC7519] or
[RFC8392]. Use of this Header Parameter is OPTIONAL.
All JPT payloads that are claim values MUST be the base64url encoding
of the UTF-8 representation of a JSON value. That said, predicate
proofs derived from payload values are not represented as claims;
they are contained in the presentation proof using algorithm-specific
representations. All CPT payloads that are claim values MUST be a
CBOR value. Likewise, CPT predicate proofs derived from payload
values are not represented as claims; they are contained in the
presentation proof using algorithm-specific representations.
Jones, et al. Expires 18 September 2025 [Page 5]
Internet-Draft json-proof-token March 2025
The following is an example JWP Issuer Protected Header that includes
a claims property:
{
"kid": "HjfcpyjuZQ-O8Ye2hQnNbT9RbbnrobptdnExR0DUjU8",
"alg": "BBS",
"claims": [
"iat",
"exp",
"family_name",
"given_name",
"email",
"address",
"age_over_21"
]
}
In this example, the "iat" and "exp" would be JSON-formatted numbers,
"family_name", "given_name" and "email" would be JSON strings (in
quotes), "address" would be a JSON object, and "age_over_21" would be
either true or false.
7. Claims ID ("cid") JWP Header Parameter
A Claims ID ("cid") value can be used as an identifier for a set of
claim names without explicitly listing them. Its use is similar to
the Key ID ("kid") header parameter.
The structure of the cid value is unspecified. For JPTs, its value
MUST be a case-sensitive string. For CPTs, its value MUST be a
binary string. Use of this JWP Header Parameter is OPTIONAL.
The cid can be used similarly to a kid in order to ensure that is it
possible to 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. Likewise, if there is an associated COSE_Key
containing the signing key information, the claims key is also
registered there as a convenient location for the claim names.
Jones, et al. Expires 18 September 2025 [Page 6]
Internet-Draft json-proof-token March 2025
When the claims array is transferred as a property in the Issuer
Protected Header, any variations of that array between JWP will be
visible to the verifier, and can leak information about the subject
or provide an additional vector for linkability. Given the privacy
design considerations around linkability, it is RECOMMENDED that the
claims are defined external to an individual JPT or CPT and either
referenced or known by the application context.
The following is an example JWP Protected Header that includes a cid:
{
"kid": "HjfcpyjuZQ-O8Ye2hQnNbT9RbbnrobptdnExR0DUjU8",
"alg": "BBS",
"cid": "guA8PAI14Gkn4273f1rR606yMbRMFg4y"
}
8. Presented Claims and Proofs
Each claim in the issued form of the JPT or CPT results in one of
three things in the presented form of the JPT or CPT: 1. A disclosed
JSON or CBOR value. 1. An indicator that the value was not
disclosed. 1. An algorithm-specific proof method.
8.1. Disclosed
A disclosed payload of a JPT is represented as a UTF8-encoded octet
string representing a valid JSON value. A disclosed payload of a CPT
is represented as a CBOR value.
8.2. Undisclosed
The placeholder indicating that a payload was not disclosed is
represented as described in Section 6 (Serializations) of
[I-D.ietf-jose-json-web-proof].
8.3. Proof Methods
Proof methods can be returned instead of a disclosed payload. These
are generated in an algorithm-specific manner from information in the
JWP's proof value.
A proof method may be custom based on the capabilities of the
algorithm.
* TBD: Describe common proof method types available:
- range
- membership
- time
Jones, et al. Expires 18 September 2025 [Page 7]
Internet-Draft json-proof-token March 2025
- knowledge
- linking
9. Example JPTs
See the examples in Appendix A.1 of
[I-D.ietf-jose-json-proof-algorithms].
10. Security Considerations
* Protected Header Minimization
11. IANA Considerations
11.1. JSON Web Proof Header Parameters Registration
This section registers the following JWP Header Parameter in the IANA
"JSON Web Proof Header Parameters" registry established by
[I-D.ietf-jose-json-web-proof].
11.1.1. Registry Contents
11.1.1.1. "claims" (Claims) Header Parameter
* Header Parameter Name: Claims
* Header Parameter JSON Label: claims
* Header Parameter CBOR Label: 10
* Header Parameter Usage Location(s): Issued
* Change Controller: IETF
* Specification Document(s): Section 6 of this specification
11.1.1.2. "cid" (Claims ID) Header Parameter
* Header Parameter Name: Claims ID
* Header Parameter JSON Label: cid
* Header Parameter CBOR Label: 11
* Header Parameter Usage Location(s): Issued
* Change Controller: IETF
* Specification Document(s): Section 7 of this specification
11.2. JSON Web Key Parameters Registry
This section registers the following JWK parameter in the IANA "JSON
Web Key Parameters" registry [IANA.JOSE] established by [RFC7517].
11.2.1. Registry Contents
* Parameter Name: claims
Jones, et al. Expires 18 September 2025 [Page 8]
Internet-Draft json-proof-token March 2025
* Parameter Description: Array of claim names
* Used with "kty" Value(s): *
* Parameter Information Class: Public
* Change Controller: IETF
* Specification Document(s): Section 7 of this specification
11.3. COSE Key Common Parameters Registry
This section registers the following COSE_Key parameter in the IANA
"COSE Key Common Parameters" registry [IANA.COSE] established by
[RFC8152].
11.3.1. Registry Contents
* Name: claims
* Label: TBD (requested assignment 6)
* CBOR Type: array
* Value Registry: CBOR Web Token Claims
* Description: Array of claim names
* Reference: Section 7 of this specification
11.4. Media Types Registry
This section registers the following media type [RFC2046] in the IANA
"Media Types" registry <xref target="IANA.MediaTypes"/> in the manner
described in [RFC6838].
11.4.1. application/jpt
The media type for a JSON Proof Token (JPT) is application/jpt.
* Type name: application
* Subtype name: jpt
* Required parameters: n/a
* Optional parameters: n/a
* Encoding considerations: 8bit; JPT values are encoded as a series
of base64url-encoded values (some of which may be the empty
string) separated by period ('.') characters.
* Security considerations: See Section 10 of this specification
* Interoperability considerations: n/a
* Published specification: This specification
* Applications that use this media type: Applications releasing
claims with zero-knowledge proofs
* Additional information:
- Magic number(s): n/a
- File extension(s): n/a
- Macintosh file type code(s): n/a
Jones, et al. Expires 18 September 2025 [Page 9]
Internet-Draft json-proof-token March 2025
* Person & email address to contact for further information: Michael
B. Jones, michael_b_jones@hotmail.com
* Intended usage: COMMON
* Restrictions on usage: none
* Author: Michael B. Jones, michael_b_jones@hotmail.com
* Change controller: IETF
* Provisional registration: No
11.4.2. application/cpt
The media type for a CBOR Proof Token (CPT) is application/cpt.
* Type name: application
* Subtype name: cpt
* Required parameters: n/a
* Optional parameters: n/a
* Encoding considerations: 8bit; CPT values are encoded as CBOR
* Security considerations: See Section 10 of this specification
* Interoperability considerations: n/a
* Published specification: This specification
* Applications that use this media type: Applications releasing
claims with zero-knowledge proofs
* Additional information:
- Magic number(s): n/a
- File extension(s): n/a
- Macintosh file type code(s): n/a
* Person & email address to contact for further information: Michael
B. Jones, michael_b_jones@hotmail.com
* Intended usage: COMMON
* Restrictions on usage: none
* Author: Michael B. Jones, michael_b_jones@hotmail.com
* Change controller: IETF
* Provisional registration: No
11.5. CoAP Content-Formats Registry
This section registers the following CoAP Content-Formats value in
the [IANA.CoAP.Formats] registry.
11.5.1. "CPT" CoAP Content-Format
The CoAP Content-Format for a CBOR Proof Token (CPT) is as follows.
* Content Type: application/cpt
* ID: TBD (requested assignment 20)
* Reference: Section 11.4.2 of this specification
12. References
Jones, et al. Expires 18 September 2025 [Page 10]
Internet-Draft json-proof-token March 2025
12.1. Normative References
[I-D.ietf-jose-json-web-proof]
Waite, D., Jones, M. B., and J. Miller, "JSON Web Proof",
Work in Progress, Internet-Draft, draft-ietf-jose-json-
web-proof-07, 21 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-jose-
json-web-proof-07>.
[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>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[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>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
12.2. Informative References
[I-D.ietf-jose-json-proof-algorithms]
Jones, M. B., Waite, D., and J. Miller, "JSON Proof
Algorithms", Work in Progress, Internet-Draft, draft-ietf-
jose-json-proof-algorithms-07, 21 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-jose-
json-proof-algorithms-07>.
[IANA.COSE]
IANA, "CBOR Object Signing and Encryption",
<https://www.iana.org/assignments/cose>.
[IANA.CWT] IANA, "CBOR Web Token",
<https://www.iana.org/assignments/cwt>.
[IANA.CoAP.Formats]
IANA, "CoAP Content-Formats",
<https://www.iana.org/assignments/core-parameters/core-
parameters.xhtml#content-formats>.
Jones, et al. Expires 18 September 2025 [Page 11]
Internet-Draft json-proof-token March 2025
[IANA.JOSE]
IANA, "JSON Object Signing and Encryption",
<https://www.iana.org/assignments/jose>.
[IANA.JWT] IANA, "JSON Web Token",
<https://www.iana.org/assignments/jwt>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
Appendix A. Acknowledgements
This work was incubated in the DIF Applied Cryptography Working Group
(https://identity.foundation/working-groups/crypto.html).
We would like to thank Brent Zundel for his valuable contributions to
this specification.
Appendix B. Document History
[[ To be removed from the final specification ]]
-08
* Defined CBOR Proof Token (CPT).
* Registered application/jpt and application/cpt media types and CPT
CoAP Content-Format.
* Made some additional references normative.
-07
* Changing primary editor
* Move claims definition from JWP, to live beside cid
Jones, et al. Expires 18 September 2025 [Page 12]
Internet-Draft json-proof-token March 2025
* Update cid registry entry to assign CBOR label
-06
* Update reference to new repository home
* Fixed #99: Discussed issued and presented forms of JPTs.
-05
* Define and register Claims ID JWP Header Parameter.
-04
* Refactoring figures and examples to be built from a common set
across all three documents
-03
* Improvements resulting from a full proofreading.
* Added examples of JSON object and JSON boolean claims.
-02
* Update example to use the current BBS algorithm
-01
* Correct cross-references within group.
-00
* Created initial working group draft based on draft-jmiller-jose-
json-proof-token-01
Authors' Addresses
Michael B. Jones
Self-Issued Consulting
Email: michael_b_jones@hotmail.com
URI: https://self-issued.info/
David Waite
Ping Identity
Email: dwaite+jwp@pingidentity.com
Jones, et al. Expires 18 September 2025 [Page 13]
Internet-Draft json-proof-token March 2025
Jeremie Miller
Ping Identity
Email: jmiller@pingidentity.com
Jones, et al. Expires 18 September 2025 [Page 14]