OAuth Status Attestations

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Table of Contents

1. Introduction

Status Attestation plays a crucial role in maintaining the integrity and trustworthiness of digital credentials, since these serve as proof that a particular digital credential, whether in JSON Web Tokens (JWT) or CBOR Web Tokens (CWT) format, has not been revoked and is still valid.¶

A digital credential may be presented to a verifier long after it has been issued. During this interval, the digital credential could potentially be invalidated for various reasons (e.g., due to the device lost or holder fraud). To ensure the digital credential's validity, the issuer provides a short-lived Status Attestation to the holder. This attestation is bound to the digital credential and can be provided to a verifier, together with the digital credential, as evidence of the digital credential's non-revocation status.¶

Status Attestation safeguards privacy and is essential in facilitating offline scenarios. In these circumstances, both the wallet and the verifier work without internet connectivity during the presentation phase; nonetheless, Status Attestation provides a method to statically validate the validity of the digital credentials, thus increasing the security of the digital credential system. By limiting the disclosure of status information, Status Attestation strikes a balance between scalability, security, and privacy.¶

+-----------------+                             +-------------------+
|                 | Requests Status Attestation |                   |
|                 |---------------------------->|                   |
| Wallet Instance |                             | Credential Issuer |
|                 | Status Attestation          |                   |
|                 |<----------------------------|                   |
+-----------------+                             +-------------------+


+-- ----------------+                             +----------+
|                   | Presents Digital Credential |          |
|  Wallet Instance  | and Status Attestation      | Verifier |
|                   |---------------------------->|          |
+-------------------+                             +----------+

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

This specification uses the terms "End-User", "Entity" as defined by OpenID Connect Core [@OpenID.Core], the term "JSON Web Token (JWT)" defined by JSON Web Token (JWT) [RFC7519].¶

Digital Credential:

A set of one or more claims about a subject made by a Credential Issuer.¶

Credential Issuer:

Entity that is responsible for the issuance of the Digital Credentials. The Issuer is responsible for the lifecycle of their issued Digital Credentials and their validity status.¶

Verifier:

Entity that relies on the validity of the Digital Credentials presented to it. This Entity, also known as a Relying Party, needs to verify the authenticity and validity of the Digital Credentials, including their revocation status, before accepting them.¶

Wallet Instance:

The digital Wallet in control of a User, also known as Wallet or Holder. It securely stores the User's Digital Credentials. It can present Digital Credentials to Verifiers and request Status Attestations from Issuers under the control of the User.¶

4. Rationale

OAuth Status Lists [@!I-D.looker-oauth-jwt-cwt-status-list] are suitable for specific scenarios, especially when the Verifier needs to verify the status of a Digital Credential at a later time after the User has presented the Digital Credential.¶

However, there are cases where the Verifier only needs to check the revocation status of a Digital Credential at the time of presentation, or situations where the Verifier should not be allowed to check the status of a Digital Credential over time due to some privacy constraints, in compliance with national privacy regulations.¶

TODO: Add an example of national privacy constraints to give the reader some intuition.¶

In scenarios where the Verifier, Credential Issuer, and OAuth Status List Provider are all part of the same domain or operate within a context where a high level of trust exists between them and the End-User, the OAuth Status List is the optimal solution; while there might be other cases where the OAuth Status List facilitates the exposure to the following privacy risks:¶

• An OAuth Status List Provider might know the association between a specific list and a Credential Issuer, especially if the latter issues a single type of Digital Credential. This could inadvertently reveal the Status List Provider which list corresponds to which Digital Credential.¶

• A Verifier retrieves an OAuth Status List by establishing a TCP/IP connection with an OAuth Status List Provider. This allows the OAuth Status List Provider to obtain the IP address of the Verifier and potentially link it to a specific Digital Credential type and Credential Issuer associated with that OAuth Status List. A malicious OAuth Status List Provider could use internet diagnostic tools, such as Whois or GeoIP lookup, to gather additional information about the Verifier. This could inadvertently disclose to the OAuth Status List Provider which Digital Credential the requester is using and from which Credential Issuer, information that should remain confidential.¶

Status Attestations differ significantly from OAuth Status Lists in several ways:¶

1. Privacy: Status Attestations are designed to be privacy-preserving. They do not require the Verifier to gather any additional information from third-party entities, thus preventing potential privacy leaks.¶

2. Static Verification: Status Attestations are designed to be statically provided to Verifiers by Wallet Instance. Once a Status Attestation is issued, it can be verified without any further communication with the Credential Issuer or any other party.¶

3. Digital Credentials Formats: Status Attestations are agnostic from the Digital Credential format to which they are bound.¶

4. Trust Model: Status Attestations operate under a model where the Verifier trusts the Credential Issuer to provide accurate status information, while the OAuth Status Lists operate under a model where the Verifier trusts the Status List Provider to maintain an accurate and up-to-date list of statuses.¶

5. Offline flow: OAuth Status List can be accessed by a Verifier when an internet connection is present. At the same time, OAuth Status List defines how to provide a static Status List Token, to be included within a Digital Credential. This requires the Wallet Instance to acquire a new Digital Credential for a specific presentation. Even if similar to the OAuth Status List Token, the Status Attestations enable the User to persistently use their preexistent Digital Credentials, as long as the linked Status Attestation is available and presented to the Verifier, and not expired.¶

5. Requirements

The general requirements for the implementation of Status Attestation are listed in this section. The Status Attestation:¶

• MUST be presented in conjunction with the Digital Credential. The Status Attestation MUST be timestamped with its issuance datetime, always referring to a previous period to the presentation time.¶

• MUST contain the expiration datetime after which the Digital Credential MUST NOT be considered valid anymore. The expiration datetime MUST be superior to the issuance datetime.¶

• enables offline use cases as it MUST be validated using a cryptographic signature and the cryptographic public key of the Credential Issuer.¶

Please note: in this specification the examples and the normative properties of Attestations are reported in accordance with the JWT standard, while for the purposes of this specification any Digital Credential or Attestation format may be used, as long as all attributes and requirements defined in this specification are satisfied, even using equivalent names or values.¶

6. Status Attestation Request

The Credential Issuer provides the Wallet Instance with a Status Attestation, which is bound to a Digital Credential. This allows the Wallet Instance to present it, along with the Digital Credential itself, to a Verifier as proof of the Digital Credential's non-revocation status.¶

The following diagram shows the Wallet Instance requesting a Status Attestation to a Credential Issuer, related to a specific Credential issued by the same Credential Issuer.¶

+-------------------+                         +--------------------+
|                   |                         |                    |
|  Wallet Instance  |                         | Credential Issuer  |
|                   |                         |                    |
+--------+----------+                         +----------+---------+
         |                                               |
         | HTTP POST /status                             |
         |  credential_pop = $CredentialPoPJWT           |
         +----------------------------------------------->
         |                                               |
         |  Response with Status Attestation JWT         |
         <-----------------------------------------------+
         |                                               |
+--------+----------+                         +----------+---------+
|                   |                         |                    |
|  Wallet Instance  |                         | Credential Issuer  |
|                   |                         |                    |
+-------------------+                         +--------------------+

The Wallet Instance sends the Status Attestation request to the Credential Issuer. The request MUST contain the Digital Credential, for which the Status Attestation is requested, and enveloped in a signed object as proof of possession. The proof of possession MUST be signed with the private key corresponding to the public key attested by the Credential Issuer and contained within the Digital Credential.¶

POST /status HTTP/1.1
Host: issuer.example.org
Content-Type: application/x-www-form-urlencoded

credential_pop=$CredentialPoPJWT

To validate that the Wallet Instance is entitled to request its Status Attestation, the following requirements MUST be satisfied:¶

• The Credential Issuer MUST verify the signature of the credential_pop object using the public key contained in the Digital Credential;¶

• the Credential Issuer MUST verify that it is the legitimate Issuer.¶

The technical and details about the credential_pop object are defined in the next section.¶

{
    "alg": "ES256",
    "typ": "status-attestation-request+jwt",
    "kid": $WIA-CNF-JWKID

}
.
{
    "iss": "0b434530-e151-4c40-98b7-74c75a5ef760",
    "aud": "https://issuer.example.org/status-attestation-endpoint",
    "iat": 1698744039,
    "exp": 1698834139,
    "jti": "6f204f7e-e453-4dfd-814e-9d155319408c",
    "credential_format": "vc+sd-jwt",
    "credential": $Issuer-Signed-JWT
}

7. Status Attestation

When a Status Attestation is requested to a Credential Issuer, the Issuer checks the status of the Digital Credential and creates a Status Attestation bound to it.¶

If the Digital Credential is valid, the Credential Issuer creates a new Status Attestation, which a non-normative example is given below.¶

{
    "alg": "ES256",
    "typ": "status-attestation+jwt",
    "kid": $ISSUER-JWKID
}
.
{
    "iss": "https://issuer.example.org",
    "iat": 1504699136,
    "exp": 1504700136,
    "credential_hash": $CREDENTIAL-HASH,
    "credential_hash_alg": "sha-256",
    "cnf": {
        "jwk": {...}
    }
}

The Status Attestation MUST contain the following claims when the JWT format is used.¶

8. Status Attestation Response

If the Status Attestation is requested for a non-existent, expired, revoked or invalid Digital Credential, the Credential Issuer MUST respond with an HTTP Response with the status code set to 404.¶

If the Digital Credential is valid, the Credential Issuer then returns the Status Attestation to the Wallet Instance, as in the following non-normative example.¶

HTTP/1.1 201 OK
Content-Type: application/json

{
    "status_attestation": "eyJhbGciOiJFUzI1Ni ...",
}

9. Credential Issuers Supporting Status Attestations

{
 "vct": "https://credentials.example.com/identity_credential",
 "given_name": "John",
 "family_name": "Doe",
 "email": "johndoe@example.com",
 "phone_number": "+1-202-555-0101",
 "address": {
   "street_address": "123 Main St",
   "locality": "Anytown",
   "region": "Anystate",
   "country": "US"
 },
 "birthdate": "1940-01-01",
 "is_over_18": true,
 "is_over_21": true,
 "is_over_65": true,
 "status": {
    "status_attestation": {
        "credential_hash_alg": "S256",
    }
 }
}

10. Presenting Status Attestations

The Wallet Instance that provides the Status Attestations SHOULD be included in the vp_token JSON array, as defined in [@OpenID4VP], the Status Attestation along with the related Digital Credential.¶

The Verifier that receives a Digital Credential supporting the Status Attestation, SHOULD:¶

• Decode and validate the Digital Credential;¶

• check the presence of status.status_attestation in the Digital Credential. If true, the Verifier SHOULD:¶

  • produce the hash of the Digital Credential using the hashing algorithm defined in status.status_attestation;¶

  • decode all the Status Attestations provided in the presentation, by matching the JWS Header parameter typ set to status-attestation+jwt and looking for the credential_hash value that matches with the hash produced at the previous point;¶

  • evaluate the validity of the Status Attestation.¶

Please note: The importance of checking the revocation status of Digital Credentials as a 'SHOULD' rather than a 'MUST' for a Verifier who gets Status Attestation for the Digital Credential stems from the fact that the decision of a Verifier to check the revocation status of Digital Credentials is not absolute and can be influenced by numerous variables. Consider as an example the case of age-over x; even if it has expired, it may still perform its intended purpose. As a result, the expiration status alone does not render it invalid. The adaptability recognizes that the need to verify revocation status may not always coincide with the actual usability of a Digital Credential, allowing Verifiers to examine and make educated conclusions based on a variety of scenarios.¶

11. Security Considerations

TODO Security¶

12. IANA Considerations

13. 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/rfc/rfc2119>.

[RFC7515]

Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, <https://www.rfc-editor.org/rfc/rfc7515>.

[RFC7516]

Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015, <https://www.rfc-editor.org/rfc/rfc7516>.

[RFC7517]

Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015, <https://www.rfc-editor.org/rfc/rfc7517>.

[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/rfc/rfc7519>.

[RFC7800]

Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)", RFC 7800, DOI 10.17487/RFC7800, April 2016, <https://www.rfc-editor.org/rfc/rfc7800>.

[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/rfc/rfc8174>.

[RFC9126]

Lodderstedt, T., Campbell, B., Sakimura, N., Tonge, D., and F. Skokan, "OAuth 2.0 Pushed Authorization Requests", RFC 9126, DOI 10.17487/RFC9126, September 2021, <https://www.rfc-editor.org/rfc/rfc9126>.

Appendix A. Acknowledgments

We would like to thank:¶

• Paul Bastien¶

• Riccardo Iaconelli¶

• Victor Näslund¶

• Giada Sciarretta¶

• Amir Sharif¶

Appendix B. Document History

TODO changelog.¶

Authors' Addresses