Internet-Draft JWT and CWT Status List July 2023
Looker & Bastian Expires 11 January 2024 [Page]
Workgroup:
Network Working Group
Internet-Draft:
draft-looker-oauth-jwt-cwt-status-list-01
Published:
Intended Status:
Informational
Expires:
Authors:
T. Looker
MATTR
P. Bastian

JWT and CWT Status List

Abstract

This specification defines status list data structures for representing the status of JSON Web Tokens (JWTs) [RFC7519] and CBOR Web Tokens (CWTs) [RFC8392]. The status list data structures themselves are also represented as JWTs or CWTs.

About This Document

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

The latest revision of this draft can be found at https://vcstuff.github.io/draft-looker-oauth-jwt-cwt-status-list/draft-looker-oauth-jwt-cwt-status-list.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-looker-oauth-jwt-cwt-status-list/.

Source for this draft and an issue tracker can be found at https://github.com/vcstuff/draft-looker-oauth-jwt-cwt-status-list.

Status of This Memo

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

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This Internet-Draft will expire on 11 January 2024.

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Table of Contents

1. Introduction

JSON Web Tokens (JWTs) [RFC7519] and CBOR Web Tokens (CWTs) [RFC8392] as secure token formats, have vast possible applications. Some of these applications can involve issuing a token whereby certain semantics about the token can change over time, which are important to be able to communicate to relying parties in an interoperable manner, such as whether the token is considered invalidated or suspended by its issuer.

This document defines Status List representations in JWT and CWT formats that describe the individual statuses of multiple Referenced Tokens, which themselves are also JWTs or CWTs. The statuses of all Referenced Tokens are conveyed via a bit array in the Status List. Each Referenced Token is allocated an index during issuance that represents its position within this bit array. The value of the bit(s) at this position correspond to the Referenced Token's status. The document also defines how an issuer of a Referenced Token references a Status List Token. Status Lists may be composed for expressing a range of Status Types. This document defines basic Status Types for the most common use cases as well as an extensibility mechanism for custom Status Types. The Status List Token may be used by an issuer in the Issuer-Holder-Verifier model to express the status of verifiable credentials (Referenced Tokens) issued by an issuer.

The following diagram depicts the basic conceptual relationship.

+------------------+                    +-------------------+
|                  |     References     |                   |
|                  |------------------->|                   |
| Referenced Token |                    | Status List Token |
|   (JWT or CWT)   |                    |    (JWT or CWT)   |
|                  |  Describes Status  |                   |
|                  |<-------------------|                   |
+------------------+                    +-------------------+

1.1. Rationale

Revocation mechanisms are an essential part for most identity ecosystems. In the past, revocation of X.509 TLS certificates has been proven difficult. Traditional certificate revocation lists (CRLs) have limited scalability; Online Certificate Status Protocol (OCSP) has additional privacy risks, since the client is leaking the requested website to a third party. OCSP stapling is addressing some of these problems at the cost of less up-to-date data. Modern approaches use accumulator-based revocation registries and Zero-Knowledge-Proofs to accommodate for this privacy gap, but face scalability issues again.

This specification seeks to find a balance between scalability, security, and privacy by minimizing the status information to mere bits (often a single bit) and compressing the resulting binary data. Thereby, a Status List may contain statuses of 100,000 or more Referenced Tokens, but still remain relatively small. Placing large amounts of Referenced Tokens into the same list also enables herd privacy relative to the Issuer.

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. Terminology

Status List:

A bit array that lists the statuses of many Referenced Tokens.

Status List Token:

A token in JWT or CWT representation that contains a Status List.

Referenced Token:

A token in JWT or CWT representation which contains a reference to a Status List Token. The information from the contained Status List may give a verifier additional information about up-to-date status of the Referenced Token.

4. JSON Web Token Representation

4.1. Referenced Token Format and Processing Requirements

The following rules apply to validating a Referenced Token in JWT representation, which references a Status List Token. Application of additional restrictions and policy are at the discretion of the verifying party.

  1. The JWT MUST contain an "iss" (issuer) claim that contains a unique string identifier for the entity that issued the JWT. In the absence of an application profile specifying otherwise, compliant applications MUST compare issuer values using the Simple String Comparison method defined in Section 6.2.1 of [RFC3986]. The value MUST be equal to that of the "iss" claim contained within the referenced Status List Token.
  2. The JWT MUST contain an "status" (status) claim conforming to the rules outlined in Section 4.1.1

The following example is the decoded header and payload of a JWT meeting the processing rules as defined above.

{
  "alg": "ES256",
  "kid": "11"
}
.
{
  "iss": "https://example.com",
  "status": {
    "idx": 0,
    "uri": "https://example.com/statuslists/1"
  }
}

4.1.1. Status Claim Format

The following rules apply to validating the "status" (status) claim

  1. The claim value MUST be a valid JSON object.
  2. The claim value object MUST contain an "idx" (index) member with a numeric value that represents the index to check for status information in the Status List for the current JWT. The value of this member MUST be a non-negative number, containing a value of zero or greater.
  3. The claim value object MUST contain a "uri" member with a string value that identifies the Status List containing the status information for the JWT. The value of this member MUST be a uri conforming to [RFC3986].

4.2. Status List JWT Format and Processing Requirements

The following rules apply to validating a JWT-based Status List Token. Application of additional restrictions and policy are at the discretion of the verifying party.

  1. The JWT MUST contain an "iss" (issuer) claim that contains a unique string identifier for the entity that issued the JWT. In the absence of an application profile specifying otherwise, compliant applications MUST compare issuer values using the Simple String Comparison method defined in Section 6.2.1 of [RFC3986]. The value MUST be equal to that of the "iss" claim contained within the Referenced Token.
  2. The JWT MUST contain a "sub" (subject) claim that contains an unique string identifier for that Referenced Token. The value MUST be equal to that of the "uri" claim contained in the "status" claim of the Referenced Token.
  3. The JWT MUST contain an "iat" (issued at) claim that identifies the time at which it was issued.
  4. The JWT MUST contain an "status_list" (status list) claim conforming to the rules outlined in Section 4.2.1.
  5. The JWT MAY contain an "exp" (expiration time) claim that conveys when it is considered expired by its issuer.
  6. The JWT MAY contain other claims.
  7. The JWT MUST be digitally signed using an asymmetric cryptographic algorithm. Relying parties MUST reject the JWT if it is using a Message Authentication Code (MAC) algorithm. Relying parties MUST reject JWTs with an invalid signature.
  8. Relying parties MUST reject JWTs that are not valid in all other respects per "JSON Web Token (JWT)" [RFC7519]. 
{
  "typ": "statuslist+jwt",
  "alg": "ES256",
  "kid": "11"
}
.
{
  "iss": "https://example.com",
  "sub": "https://example.com/statuslists/1",
  "iat": 1683560915,
  "exp": 1686232115,
  "status_list": {
    "bits": 1,
    "lst": "H4sIAMo_jGQC_9u5GABc9QE7AgAAAA"
  }
}

4.2.1. Status List Claim Format

The following rules apply to validating the "status_list" (status list) claim

  1. The claim value MUST be a valid JSON object.
  2. The claim value object MUST contain a "bits" (bit size) member with an numeric value that represents the number of bits per Referenced Token in the Status List ("lst") of the Status List JWT. The allowed values for "bits" are 1,2,4 and 8.
  3. The claim value object MUST contain a "lst" (list) member with a string value that represents the status values for all the tokens it conveys statuses for. The value MUST be computed using the algorithm described in Section 4.2.2.

4.2.2. Status List Encoding

Each status of a Referenced Token MUST be represented with a bit size of 1,2,4, or 8. Therefore up to 2,4,16, or 256 statuses for a Referenced Token are possible, depending on the bit size. This limitation is intended to limit bit manipulation necessary to a single byte for every operation and thus keeping implementations simpler and less error prone.

  1. The overall Status List is encoded as a byte array. Depending on the bitsize, each byte corresponds to 8/(#bit-size) statuses (8,4,2, or 1). The status of each Referenced Token is identified using the index that maps to one or more specific bits within the byte array. The index starts counting at 0 and ends with "size" - 1 (being the last valid entry). The bits within an array are counted from least significant bit "0" to the most significant bit ("7"). All bits of the byte array at a particular index are set to a status value.
  2. The complete byte array is compressed using gZIP [RFC1952].
  3. The result of the gZIP compression is then base64url-encoded, as defined in Section 2 of [RFC7515].

5. Status Types

This document defines potential statuses of Referenced Tokens as Status Type values. If the Status List contains more than one bit per token (as defined by "bits" in the Status List), then the whole value of bits MUST describe one value. A Status List can not represent multiple statuses per Referenced Token.

The registry in this document describes the basic Status Type values required for the most common use cases. Additional values may defined for particular use cases.

5.1. Status Types Values

A status describes the state, mode, condition or stage of an entity that is described by the status list. Status Types MUST be numeric values between 0 and 255. Status types described by this specification comprise: - 0x00 - "VALID" - The status of the Token is valid, correct or legal. - 0x01 - "INVALID" - The status of the Token is revoked, annulled, taken back, recalled or cancelled. This state is irreversible. - 0x02 - "SUSPENDED" - The status of the Token is temporarily invalid, hanging, debarred from privilege. This state is reversible.

The issuer of the Status List Token MUST choose an adequate "bits" (bit size) to be able to describe the required Status Types for the application.

6. Example JWT Status Lists

6.1. Example Status List with 1-Bit Status Values

In this example, the Status List is used as a revocation list. It only requires the Status Types "VALID" and "INVALID"; therefore a "bits" of 1 is sufficient.

This example Status List represents the statuses of 16 Referenced Tokens, requiring 16 bits (2 bytes) of status.

status[0] = 1
status[1] = 0
status[2] = 0
status[3] = 1
status[4] = 1
status[5] = 1
status[6] = 0
status[7] = 1
status[8] = 1
status[9] = 1
status[10] = 0
status[11] = 0
status[12] = 0
status[13] = 1
status[14] = 0
status[15] = 1

These bits are concatenated:

byte             0                  1               2
bit       7 6 5 4 3 2 1 0    7 6 5 4 3 2 1 0    7
         +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+  +-+...
values   |1|0|1|1|1|0|0|1|  |1|0|1|0|0|0|1|1|  |0|...
         +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+  +-+...
index     7 6 5 4 3 2 1 0   15   ...  10 9 8   23
         \_______________/  \_______________/
                0xB9               0xA3

Resulting in the byte array:

byte_array = [0xB9, 0xA3]

After compression and base64url encoding, the generated Status List is:

"status_list": {
   "bits": 1,
   "lst": "H4sIAMo_jGQC_9u5GABc9QE7AgAAAA"
}

6.2. Example Status List with 2-Bit Status Values

In thisexample, the Status List additionally includes the Status Type "SUSPENDED. As the Status Type value for "SUSPENDED" is 0x02 and does not fit into 1 bit, the "bits" is required to be 2.

This example Status List represents the status of 12 Referenced Tokens, requiring 24 bits (3 bytes) of status.

status[0] = 1
status[1] = 2
status[2] = 0
status[3] = 3
status[4] = 0
status[5] = 1
status[6] = 0
status[7] = 1
status[8] = 1
status[9] = 2
status[10] = 3
status[11] = 3

These bits are concatenated:

byte             0                  1                  2
bit       7 6 5 4 3 2 1 0    7 6 5 4 3 2 1 0    7 6 5 4 3 2 1 0
         +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+
values   |1|1|0|0|1|0|0|1|  |0|1|0|0|0|1|0|0|  |1|1|1|1|1|0|0|1|
         +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+  +-+-+-+-+-+-+-+-+
          \ / \ / \ / \ /    \ / \ / \ / \ /    \ / \ / \ / \ /
status     3   0   2   1      1   0   1   0      3   3   2   1
index      3   2   1   0      7   6   5   4      11  10  9   8
           \___________/      \___________/      \___________/
                0xC9               0x44               0xF9

Resulting in the byte array:

byte_array = [0xC9, 0x44, 0xF9]

After compression and base64url encoding, the generated Status List is:

"status_list": {
   "bits": 2,
   "lst": "H4sIAMo_jGQC_zvp8hMAZLRLMQMAAAA"
}

7. CWT Representations

TBD Define parallel CWT representations for Status Lists and Referenced Tokens.

TBD Declare whether JWT and CWT representations can be used interchangeably by the same issuer. For instance, declare whether a status list can reference both JWT and CWT tokens.

8. Security Considerations

8.1. Correct decoding and parsing of the encoded status list

TODO elaborate on risks of incorrect parsing/decoding leading to erroneous status data

8.2. Cached and Stale status lists

TODO consumers/Verifiers of the status list should be aware if they fetch the up-to-date data

8.3. Authorized access to the Status List

TODO elaborate on authorization mechanisms preventing misuse and profiling as described in privacy section

8.4. History

TODO elaborate on status list only providing the up-to date/latest status, no historical data, may be provided by the underlying hosting architecture

9. Privacy Considerations

9.1. Herd Privacy

TODO elaborate on herd privacy, size of the status list

9.2. Profiling

TODO elaborate on Verifiers regularly fetching the status list to create a profile, possible countermeasures with authorized access to the status list

9.3. Correlation Risks and Tracking

TODO elaborate on Issuer-Verifier correlation and Verifier-Verifier correlation as the status list introduces unique,trackable data TODO elaborate on issuers avoiding sequential usage of indices and status lists TODO elaborate that a status list only gives information about the maximum number of possible statuses that a list conveys, issuers are recommended to pre-allocate lists, use dead entries that are never assigned or other obfuscation mechanisms

9.4. Malicious Issuers

TODO elaborate on issuers generating unique status lists per Referenced Token that do not offer herd privacy

9.5. Hosting Service (what's a better name here?)

TODO elaborate on increased privacy if the status list is hosted by a third party instead of the issuer reducing tracking possiblities TODO evaluate deifnition of Status List Provider? An entity that hosts the Status List as a resource for potential verifiers. The Status List Provider may be the issuer of the Status List but may also be outsourced to a trusted third party.

10. IANA Considerations

This document specifies no IANA actions.

11. Normative References

[RFC1952]
Deutsch, P., "GZIP file format specification version 4.3", RFC 1952, DOI 10.17487/RFC1952, , <https://www.rfc-editor.org/rfc/rfc1952>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3986]
Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <https://www.rfc-editor.org/rfc/rfc3986>.
[RFC7515]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, , <https://www.rfc-editor.org/rfc/rfc7515>.
[RFC7519]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, , <https://www.rfc-editor.org/rfc/rfc7519>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8392]
Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, , <https://www.rfc-editor.org/rfc/rfc8392>.

Acknowledgments

We would like to thank Christian Bormann, Michael B. Jones, Torsten Lodderstedt, and Kristina Yasuda for their valuable contributions to this specification.

Document History

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Authors' Addresses

Tobias Looker
MATTR
Paul Bastian