]> Dipartimento per la trasformazione digitale

gi.demarco@innovazione.gov.it

Transmute

orie@transmute.industries

Istituto Poligrafico e Zecca dello Stato

fa.marino@ipzs.it

digital credentials status list revocation Status Attestation is a signed object that demonstrates the validity status of a digital credential. These attestations are ephemeral and periodically provided to holders, who can present these to Verifiers along with the corresponding digital credentials. The approach outlined in this document makes the verifiers able to check the non-revocation of a digital credential without requiring to query any third-party entities. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Source for this draft and an issue tracker can be found at .

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proof that a particular digital credential, whether in JSON Web Tokens (JWT) or CBOR Web Tokens (CWT) format, has not been revoked and is still valid.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. | | | Wallet Instance | | Credential Issuer | | | Status Attestation | | | |<----------------------------| | +-----------------+ +-------------------+ +-- ----------------+ +----------+ | | Presents Digital Credential | | | Wallet Instance | and Status Attestation | Verifier | | |---------------------------->| | +-------------------+ +----------+ ]]>

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.

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) .

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.

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.

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.

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. | | | 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. 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.

Digital Credential Proof of Possession The Wallet Instance that holds a Digital Credential, when requests a Status Attestation, MUST demonstrate the proof of possession of the Digital Credential to the Credential Issuer. The proof of possession is made by enclosing the Digital Credential in an object (JWT) signed with the private key that its related public key is referenced in the Digital Credential. Below is a non-normative example of a Credential proof of possession with the JWT headers and payload are represented without applying signature and encoding, for better readability: When the JWT format is used, the JWT MUST contain the parameters defined in the following table.

JOSE Header	Description	Reference
typ	It MUST be set to status-attestation-request+jwt	Section 4.1.1
alg	A digital signature algorithm identifier such as per IANA "JSON Web Signature and Encryption Algorithms" registry. It MUST NOT be set to none or any symmetric algorithm (MAC) identifier.	Section 4.1.1
kid	Unique identifier of the JWK used for the signature of the Status Attestation Request, it MUST match the one contained in the Credential cnf.jwk.

JOSE Payload	Description	Reference
iss	Wallet identifier.	,
aud	It MUST be set to the identifier of the Credential Issuer.	,
exp	UNIX Timestamp with the expiration time of the JWT.	,
iat	UNIX Timestamp with the time of JWT issuance.	,
jti	Unique identifier for the JWT.	Section 4.1.7
credential_format	The data format of the Credential. Eg: vc+sd-jwt for SD-JWT, vc+mdoc for ISO/IEC 18013-5 MDOC CBOR [@ISO.18013-5]	this specification
credential	It MUST contain the Credential according to the data format given in the format claim.	this specification

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

JOSE Header	Description	Reference
alg	A digital signature algorithm identifier such as per IANA "JSON Web Signature and Encryption Algorithms" registry. It MUST NOT be set to none or to a symmetric algorithm (MAC) identifier.	,
typ	It MUST be set to status-attestation+jwt.	, and this specification
kid	Unique identifier of the Issuer JWK.

JOSE Payload	Description	Reference
iss	It MUST be set to the identifier of the Issuer.	,
iat	UNIX Timestamp with the time of the Status Attestation issuance.	,
exp	UNIX Timestamp with the expiry time of the Status Attestation.	,
credential_hash	Hash value of the Digital Credential the Status Attestation is bound to.	this specification
credential_hash_alg	The Algorithm used of hashing the Digital Credential to which the Status Attestation is bound. The value SHOULD be set to S256.	this specification
cnf	JSON object containing the cryptographic key binding. The cnf.jwk value MUST match with the one provided within the related Digital Credential.	Section 3.1

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.

Credential Issuers Supporting Status Attestations

Credential Issuer Metadata The Credential Issuers that uses the Status Attestations MUST include in their OpenID4VCI [@!OpenID.VCI] metadata the claim status_attestation_endpoint, which its value MUST be an HTTPs URL indicating the endpoint where the Wallet Instances can request Status Attestations.

Issued Digital Credentials The Credential Issuers that uses the Status Attestations SHOULD include in the issued Digital Credentials the object status with the JSON member status_attestation set to a JSON Object containing the following member:

• credential_hash_alg. REQUIRED. The Algorithm used of hashing the Digital Credential to which the Status Attestation is bound. The value SHOULD be set to S256.

The non-normative example of an unsecured payload of an SD-JWT VC is shown below.

• TODO: alignments with the OAuth2 Status List schema and IANA registration.

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.

Security Considerations TODO Security

IANA Considerations

JSON Web Token Claims Registration This specification requests registration of the following Claims in the IANA "JSON Web Token Claims" registry [@IANA.JWT] established by .

• Claim Name: credential_format
• Claim Description: The Digital Credential format the Status Attestation is bound to.
• Change Controller: IETF
• Specification Document(s): [[ (#digital-credential-proof-of-possession) of this specification ]]

• Claim Name: credential
• Claim Description: The Digital Credential the Status Attestation is bound to.
• Change Controller: IETF
• Specification Document(s): [[ (#digital-credential-proof-of-possession) of this specification ]]

• Claim Name: credential_hash
• Claim Description: Hash value of the Digital Credential the Status Attestation is bound to.
• Change Controller: IETF
• Specification Document(s): [[ (#status-attestation) of this specification ]]

• Claim Name: credential_hash_alg
• Claim Description: The Algorithm used of hashing the Digital Credential to which the Status Attestation is bound.
• Change Controller: IETF
• Specification Document(s): [[ (#status-attestation) of this specification ]]

Media Type Registration This section requests registration of the following media types [@RFC2046] in the "Media Types" registry [@IANA.MediaTypes] in the manner described in [@RFC6838]. To indicate that the content is an JWT-based Status List:

• Type name: application
• Subtype name: status-attestation-request+jwt
• Required parameters: n/a
• Optional parameters: n/a
• Encoding considerations: binary; A JWT-based Status Attestation Request object is a JWT; JWT 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 (#Security) of [[ this specification ]]
• Interoperability considerations: n/a
• Published specification: [[ this specification ]]
• Applications that use this media type: Applications using [[ this specification ]] for updated status information of tokens
• Fragment identifier considerations: n/a
• Additional information:
  • File extension(s): n/a
  • Macintosh file type code(s): n/a
• Person & email address to contact for further information: Giuseppe De Marco, gi.demarco@innovazione.gov.it
• Intended usage: COMMON
• Restrictions on usage: none
• Author: Giuseppe De Marco, gi.demarco@innovazione.gov.it
• Change controller: IETF
• Provisional registration? No

To indicate that the content is an CWT-based Status List:

• Type name: application
• Subtype name: status-attestation+jwt
• Required parameters: n/a
• Optional parameters: n/a
• Encoding considerations: binary
• Security considerations: See (#Security) of [[ this specification ]]
• Interoperability considerations: n/a
• Published specification: [[ this specification ]]
• Applications that use this media type: Applications using [[ this specification ]] for status attestation of tokens and Digital Credentials
• Fragment identifier considerations: n/a
• Additional information:
  • File extension(s): n/a
  • Macintosh file type code(s): n/a
• Person & email address to contact for further information: Giuseppe De Marco, gi.demarco@innovazione.gov.it
• Intended usage: COMMON
• Restrictions on usage: none
• Author: Giuseppe De Marco, gi.demarco@innovazione.gov.it
• Change controller: IETF
• Provisional registration? No

Normative References JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification. JSON Web Encryption (JWE) represents encrypted content using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries defined by that specification. Related digital signature and Message Authentication Code (MAC) capabilities are described in the separate JSON Web Signature (JWS) specification. A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data structure that represents a cryptographic key. This specification also defines a JWK Set JSON data structure that represents a set of JWKs. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries established by that specification. JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted. This specification describes how to declare in a JSON Web Token (JWT) that the presenter of the JWT possesses a particular proof-of- possession key and how the recipient can cryptographically confirm proof of possession of the key by the presenter. Being able to prove possession of a key is also sometimes described as the presenter being a holder-of-key. This document defines the pushed authorization request (PAR) endpoint, which allows clients to push the payload of an OAuth 2.0 authorization request to the authorization server via a direct request and provides them with a request URI that is used as reference to the data in a subsequent call to the authorization endpoint. 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. 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.

Acknowledgments We would like to thank:

• Paul Bastien
• Riccardo Iaconelli
• Victor Näslund
• Giada Sciarretta
• Amir Sharif

Document History TODO changelog.