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%%% title = "OpenID4VC High Assurance Interoperability Profile with SD-JWT VC - draft 01" abbrev = "openid4vc-high-assurance-interoperability-profile-sd-jwt-vc" ipr = "none" workgroup = "Digital Credentials Protocols" keyword = ["security", "openid4vc", "sd-jwt", "sd-jwt-vc"]

[seriesInfo] name = "Internet-Draft" value = "openid4vc-high-assurance-interoperability-profile-sd-jwt-vc-1_0-01" status = "standard"

[[author]] initials="K." surname="Yasuda" fullname="Kristina Yasuda" organization="SPRIND" [author.address] email = "kristina.yasuda@sprind.org"

[[author]] initials="T." surname="Lodderstedt" fullname="Torsten Lodderstedt" organization="sprind.org" [author.address] email = "torsten@lodderstedt.net"

%%%

.# Abstract

This document defines a profile of OpenID for Verifiable Credentials in combination with the credential format SD-JWT VC. The aim is to select features and to define a set of requirements for the existing specifications to enable interoperability among Issuers, Wallets and Verifiers of Credentials where a high level of security and privacy is required. The profiled specifications include OpenID for Verifiable Credential Issuance [@!OIDF.OID4VCI], OpenID for Verifiable Presentations [@!OIDF.OID4VP], Self-Issued OpenID Provider v2 [@!OIDF.SIOPv2], and SD-JWT VC [@!I-D.ietf-oauth-sd-jwt-vc].

{mainmatter}

Introduction

This document defines a set of requirements for the existing specifications to enable interoperability among Issuers, Wallets and Verifiers of Credentials where a high level of security and privacy is required. This document is an interoperability profile that can be used by implementations in various contexts, be it a certain industry or a certain regulatory environment.

This document is not a specification, but a profile. It refers to the specifications required for implementations to interoperate among each other and for the optionalities mentioned in the referenced specifications, defines the set of features to be mandatory to implement.

The profile uses OpenID for Verifiable Credential Issuance [@!OIDF.OID4VCI] and OpenID for Verifiable Presentations [@!OIDF.OID4VP] as the base protocols for issuance and presentation of Credentials, respectively. The credential format used is SD-JWT VC as specified in [@!I-D.ietf-oauth-sd-jwt-vc]. Additionally, considerations are given on how deployments can perform a combined issuance of credentials in both SD-JWT VC and ISO mdoc [@ISO.18013-5] formats.

A full list of the open standards used in this profile can be found in Overview of the Open Standards Requirements (reference).

Audience Target audience/Usage

The audience of the document is implementers that require a high level of security and privacy for their solutions. A non-exhaustive list of the interested parties includes eIDAS 2.0, California Department of Motor Vehicles, Open Wallet Foundation (OWF), IDunion, GAIN, and the Trusted Web project of the Japanese government, but is expected to grow to include other jurisdictions and private sector companies.

Terminology

This specification uses the terms "Holder", "Issuer", "Verifier", and "Verifiable Credential" as defined in [@!I-D.ietf-oauth-sd-jwt-vc].

Scope

The following aspects are in scope of this interoperability profile:

  • Protocol for issuance of the Verifiable Credentials (can be both remote and in-person) (OID4VCI)
  • Protocol for online presentation of Verifiable Credentials (can be both remote and in-person) (OID4VP)
  • Protocol for User Authentication by the Wallet at a Verifier (SIOP v2)
  • Wallet Attestation (during Credential issuance)
  • Credential Format (SD-JWT VC)
  • Status Management of the Credentials, including revocation
  • Cryptographic Holder Binding
  • Issuer key resolution
  • Issuer identification (as prerequisite for trust management)
  • Crypto Suites

Assumptions made are the following:

  • The issuers and verifiers cannot pre-discover wallet’s capability
  • The issuer is talking to the wallet supporting the features defined in this profile (via wallet invocation mechanism)
  • There are mechanisms in place for the verifiers and issuers to discover each other’s capability

Out of Scope

The following items are out of scope for the current version of this document, but might be added in future versions:

  • Trust Management, i.e. authorization of an issuer to issue certain types of credentials, authorization of the Wallet to be issued certain types of credentials, authorization of the Verifier to receive certain types of credentials.
  • Protocol for presentation of Verifiable Credentials for offline use-cases, e.g. over BLE.

Scenarios/Business Requirements

  • Combined Issuance of SD-JWT VC and mdoc
  • Both issuer-initiated and wallet-initiated issuance
  • eIDAS PID and (Q)EAA as defined in eIDAS ARF 1.0

Standards Requirements

Unless explicitly stated, all normative requirements apply to all participating entities: Issuers, Wallets and Verifiers.

(as defined in this profile) Issuer Wallet Verifier
OID4VP N/A MUST MUST
OID4VCI MUST MUST N/A
SIOPv2 N/A MUST SHOULD
SD-JWT VC profile as defined in (#sd-jwt-vc) MUST MUST MUST

OpenID for Verifiable Credential Issuance

Implementations of this profile:

  • MUST support both pre-auth code flow and authorization code flow.
  • MUST support protocol extensions for the SD-JWT VC credential format profile as defined in (#vc_sd_jwt_profile).
  • MUST support sender-constrained tokens using the mechanism defined in [@!RFC9449].
  • MUST support [@!RFC7636] with S256 as the code challenge method.

Both Wallet initiated and Issuer initiated issuance is supported.

Credential Offer

  • The Grant Types authorization_code and urn:ietf:params:oauth:grant-type:pre-authorized_code MUST be supported as defined in Section 4.1.1 in [@!OIDF.OID4VCI]
  • For Grant Type authorization_code, the Issuer MUST include a scope value in order to allow the Wallet to identify the desired credential type. The wallet MUST use that value in the scope Authorization parameter. For Grant Type urn:ietf:params:oauth:grant-type:pre-authorized_code, the pre-authorized code is used by the issuer to identify the credential type(s).
  • As a way to invoke the Wallet, at least a custom URL scheme haip:// MUST be supported. Implementations MAY support other ways to invoke the wallets as agreed by trust frameworks/ecosystems/jurisdictions, not limited to using other custom URL schemes.

Note: The Authorization Code flow does not require a Credential Offer from the Issuer to the Wallet. However, it is included in the feature set of the Credential Offer because it might be easier to implement with existing libraries and on top of existing implementations than the pre-authorized code Grant Type.

Both sending Credential Offer same-device and cross-device is supported.

Authorization Endpoint

  • MUST use Pushed Authorization Requests (PAR) [@!RFC9126] to send the Authorization Request.
  • Wallets MUST authenticate itself at the PAR endpoint using the same rules as defined in (#token-endpoint) for client authentication at the token endpoint.
  • MUST use the scope parameter to communicate credential type(s) to be issued. The scope value MUST map to a specific Credential type. The scope value may be pre-agreed, obtained from the Credential Offer, or the Credential Issuer Metadata.
  • The client_id value in the PAR request MUST be a string that the Wallet has used as the sub value in the client attestation JWT.

Token Endpoint {#token-endpoint}

  • The Wallets MUST perform client authentication as defined in [@!I-D.ietf-oauth-attestation-based-client-auth].
  • Refresh tokens MUST be supported for credential refresh.
  • The Wallet Attestation JWT scheme is defined in (#wallet-attestation-schema).

Note: It is RECOMMENDED to use ephemeral client attestation JWTs for client authentication in order to prevent linkability across Credential Issuers.

Note: Issuers should be mindful of how long the usage of the refresh token is allowed to refresh a credential, as opposed to starting the issuance flow from the beginning. For example, if the User is trying to refresh a credential more than a year after its original issuance, the usage of the refresh tokens is NOT RECOMMENDED.

Wallet Attestation Schema {#wallet-attestation-schema}

Wallets MUST use attestations following the definition given in [@!I-D.ietf-oauth-attestation-based-client-auth].

In addition to this definition, the Wallet Attestation MAY contain the following claims in the cnf element:

  • key_type: OPTIONAL. JSON String that asserts the security mechanism the Wallet uses to manage the private key associated with the public key given in the cnf claim. This mechanism is based on the capabilities of the execution environent of the Wallet, this might be a secure element (in case of a wallet residing on a smartphone) or a Cloud-HSM (in case of a cloud Wallet). This specification defines the following values for key_type:
    • software: It MUST be used when the Wallet uses software-based key management.
    • hardware: It MUST be used when the wallet uses hardware-based key management.
    • tee: It SHOULD be used when the Wallet uses the Trusted Execution Environment for key management.
    • secure_enclave: It SHOULD be used when the Wallet uses the Secure Enclave for key management.
    • strong_box: It SHOULD be used when the Wallet uses the Strongbox for key management.
    • secure_element: It SHOULD be used when the Wallet uses a Secure Element for key management.
    • hsm: It SHOULD be used when the Wallet uses Hardware Security Module (HSM).
  • user_authentication: OPTIONAL. JSON String that asserts the security mechanism the Wallet uses to authenticate the user to authorize access to the private key associated with the public key given in the cnf claim. This specification defines the following values for user_authentication:
    • system_biometry: It MUST be used when the key usage is authorized by the mobile operating system using a biometric factor.
    • system_pin: It MUST be used when the key usage is authorized by the mobile operating system using personal identification number (PIN).
    • internal_biometry: It MUST be used when the key usage is authorized by the Wallet using a biometric factor.
    • internal_pin: It MUST be used when the key usage is authorized by the Wallet using PIN.
    • secure_element_pin It MUST be used when the key usage is authorized by the secure element managing the key itself using PIN.

The Wallet Attestation MAY also contain the following claim:

  • aal: OPTIONAL. JSON String asserting the authentication level of the Wallet and the key as asserted in the cnf claim.

To obtain the issuer's Public key for verification, wallet attestions MUST support web-based key resolution as defined in Section 5 of [@!I-D.ietf-oauth-sd-jwt-vc]. The JOSE header kid MUST be used to identify the respective key.

This is an example of a Wallet Instance Attestation:

{
  "typ": "wallet-attestation+jwt",
  "alg": "ES256",
  "kid": "1"
}
.
{
  "iss": "<identifier of the issuer of this wallet attestation>",
  "sub": "<`client_id` of the OAuth client>",
  "iat": 1516247022,
  "exp": 1541493724,
  "aal" : "https://trust-list.eu/aal/high",
  "cnf": {
    "jwk": {
      "kty": "EC",
      "crv": "P-256",
      "x": "TCAER19Zvu3OHF4j4W4vfSVoHIP1ILilDls7vCeGemc",
      "y": "ZxjiWWbZMQGHVWKVQ4hbSIirsVfuecCE6t4jT9F2HZQ"
    },
    "key_type": "strong_box",
    "user_authentication": "system_pin",
  }
}

Credential Endpoint

  • The JWT proof type MUST be supported.

Server Metadata

  • The Credential Issuer MUST publish a mapping of every Credential Type it supports to a scope value.

OpenID for Verifiable Presentations

  • MUST support protocol extensions for SD-JWT VC credential format profile as defined in this specification (#vc_sd_jwt_profile).
  • As a way to invoke the Wallet, at least a custom URL scheme haip:// MUST be supported. Implementations MAY support other ways to invoke the wallets as agreed by trust frameworks/ecosystems/jurisdictions, not limited to using other custom URL schemes.
  • Response type MUST be vp_token.
  • Response mode MUST be direct_post. The Verifier MUST return redirect_uri in response to the HTTP POST request from the Wallet, where the Wallet redirects the User to, as defined in Section 6.2 of [@!OIDF.OID4VP]. Implementation considerations for the response mode direct_post are given in Section 11.5 of [@!OIDF.OID4VP].
  • Authorization Request MUST be sent using the request_uri parameter as defined in JWT-Secured Authorization Request (JAR) [@!RFC9101].
  • client_id_scheme parameter MUST be present in the Authorization Request.
  • client_id_scheme value MUST be either x509_san_dns or verifier_attestation. The Wallet MUST support both. The Verifier MUST support at least one.
  • To obtain the issuer's public key for verification, verifiers MUST support Web-based key resolution, as defined in Section 5 of [@!I-D.ietf-oauth-sd-jwt-vc]. The JOSE header kid MUST be used to identify the respective key.
  • Presentation Definition JSON object MUST be sent using a presentation_definition parameter.
  • The following features from the DIF Presentation Exchange v2.0.0 MUST be supported. A JSON schema for the supported features is in (#presentation-definition-schema):
* In the `presentation_definition` object, `id`, `input_descriptors` and `submission_requirements` properties MUST be supported.
* In the `input-descriptors` object, `id`, `name`, `purpose`, `group`, `format`, and `constraints` properties MUST be supported. In the `constraints` object, `limit_disclosure`, and `fields` properties MUST be supported. In the `fields` object, `path` and `filter` properties MUST be supported. A `path` MUST contain exactly one entry with a static path to a certain claim. A `filter` MUST only contain `type` elements of value `string` and `const` elements.
* In the `submission_requirements` object, `name`, `rule (`pick` only)`, `count`, `from` properties MUST be supported.

Self-Issued OP v2

To authenticate the user, subject identifier in a Self-Issued ID Token MUST be used as defined in [@!OIDF.SIOPv2].

  • As a way to invoke the Wallet, at least a custom URL scheme haip:// MUST be supported. Implementations MAY support other ways to invoke the wallets as agreed by trust frameworks/ecosystems/jurisdictions, not limited to using other custom URL schemes.
  • subject_syntax_types_supported value MUST be urn:ietf:params:oauth:jwk-thumbprint

SD-JWT VCs {#sd-jwt-vc}

As credential format, SD-JWT VCs as defined in [@!I-D.ietf-oauth-sd-jwt-vc] MUST be used.

In addition, this profile defines the following additional requirements.

  • Compact serialization MUST be supported as defined in [@!I-D.ietf-oauth-selective-disclosure-jwt]. JSON serialization MAY be supported.
  • The following JWT Claims MUST be supported Content (differentiate issuance & presentation)
Claim SD-JWT as issued by the Issuer Normative Definition
iss MUST [@!RFC7519], Section 4.1.1
iat MUST [@!RFC7519], Section 4.1.6
exp SHOULD (at the discretion of the issuer) [@!RFC7519], Section 4.1.4
cnf MUST [@!RFC7800]
vct MUST [@!I-D.ietf-oauth-sd-jwt-vc]
status SHOULD (at the discretion of the issuer) [@!I-D.ietf-oauth-status-list]
  • The Issuer MUST NOT make any of the JWT Claims in the table above to be selectively disclosable, so that they are always present in the SD-JWT-VC presented by the Holder.
  • It is at the discretion of the Issuer whether to use exp claim and/or a status claim to express the validity period of an SD-JWT-VC. The wallet and the verifier MUST support both mechanisms.
  • The iss claim MUST be an HTTPS URL. The iss value is used to obtain Issuer’s signing key as defined in (#issuer-key-resolution).
  • The vct JWT claim as defined in [@!I-D.ietf-oauth-sd-jwt-vc].
  • The cnf claim [@!RFC7800] MUST conform to the definition given in [@!I-D.ietf-oauth-sd-jwt-vc]. Implementations conforming to this profile MUST include the JSON Web Key [@!RFC7517] in the jwk sub claim.

Note: Currently this profile only supports presentation of credentials with cryptographic Holder Binding: the holder's signature is required to proof the credential is presented by the holder it was issued to. This profile might support claim-based and biometrics-based holder binding once OpenID for Verifiable Credentials adds support for other forms of Holder Binding. See https://bitbucket.org/openid/connect/issues/1537/presenting-vc-without-a-vp-using-openid4vp

Note: Re-using the same Credential across Verifiers, or re-using the same JWK value across multiple Credentials gives colluding Verifiers a mechanism to correlate the User. There are currently two known ways to address this with SD-JWT VCs. First is to issue multiple instances of the same credentials with different JWK values, so that if each instance of the credential is used at only one Verifier, it can be reused multiple times. Another is to use each credential only once (ephemeral credentials). It is RECOMMENDED to adopt one of these mechanisms.

Note: If there is a requirement to communicate information about the verification status and identity assurance data of the claims about the subject, the syntax defined by [@!OIDF.ekyc-ida] SHOULD be used. It is up to each jurisdiction and ecosystem, whether to require it to the implementers of this profile.

Note: If there is a requirement to provide the Subject’s identifier assigned and maintained by the Issuer, the sub claim MAY be used. There is no requirement for a binding to exist between the sub and cnf claims. See the Implementation Considerations section in [@!I-D.ietf-oauth-sd-jwt-vc].

Note: In some credential types, it is not desirable to include an expiration date (eg: diploma attestation). Therefore, this profile leaves its inclusion to the Issuer, or the body defining the respective credential type.

Issuer identification and key resolution to validate an issued Credential {#issuer-key-resolution}

This profile supports two ways to represent and resolve the key required to validate the issuer signature of an SD-JWT VC, the web PKI-based key resolution and the x.509 certificates.

  • Web-based key resolution: The key used to validate the Issuer’s signature on the SD-JWT VC MUST be obtained from the SD-JWT VC issuer's metadata as defined in Section 5 of [@!I-D.ietf-oauth-sd-jwt-vc]. The JOSE header kid MUST be used to identify the respective key.
  • x.509 certificates: the SD-JWT VC contains the issuer's certificate along with a trust chain in the x5c JOSE header. In this case, the iss value MUST be an URL with a FQDN matching a dNSName Subject Alternative Name (SAN) [@!RFC5280] entry in the leaf certificate.

Note: The issuer MAY decide to support both options. In which case, it is at the discretion of the Wallet and the Verifier which key to use for the issuer signature validation.

Cryptographic Holder Binding between VC and VP

  • For Cryptographic Holder Binding, a KB-JWT, as defined in [@!I-D.ietf-oauth-sd-jwt-vc], MUST always be present when presenting an SD-JWT VC.

OpenID4VC Credential Format Profile {#vc_sd_jwt_profile}

A Credential Format Profile for Credentials complying with IETF SD-JWT VCs [@!I-D.ietf-oauth-sd-jwt-vc] is defined in Annex A.3 of [@!OIDF.OID4VCI] and Annex A.4 of [@!OIDF.OID4VP].

Crypto Suites

Issuers, holders and verifiers MUST support P-256 (secp256r1) as a key type with ES256 JWT algorithm for signing and signature validation whenever this profiles requires to do so:

  • SD-JWT-VC
  • Wallet Instance Attestation
  • DPoP
  • HB JWT
  • Authorization request during presentation

SHA256 MUST be supported by all the entities as the hash algorithm to generate and validate the digests in the SD-JWT VC.

Note: When using this profile with other cryptosuites, it is recommended to be explicit about which entity is required to support which curve for signing and/or signature validation

Implementations Considerations

Validity Period of the Signature and the Claim Values

iat and exp JWT claims express both the validity period of both the signature and the claims about the subject, unless there is a separate claim used to express the validity of the claims.

{backmatter}

<title>OpenID for Verifiable Credential Issuance</title> yes.com Microsoft Mattr <title>OpenID for Verifiable Presentations</title> Spruce Systems, Inc. yes.com Microsoft Convergence.tech Mattr <title>Self-Issued OpenID Provider V2</title> Microsoft Microsoft yes.com <title>OpenID Connect for Identity Assurance 1.0</title> yes yes Considrd.Consulting Ltd Santander 1&1 Mail & Media Development & Technology GmbH KDDI Corporation <title>ISO/IEC 18013-5:2021 Personal identification — ISO-compliant driving license — Part 5: Mobile driving license (mDL) application</title> ISO/IEC JTC 1/SC 17 Cards and security devices for personal identification <title>Verifiable Credentials Data Model v2.0</title> Digital Bazaar Digital Bazaar Crossword Cybersecurity PLC

Combined Issuance of SD-JWT VC and mdocs

  • If combined issuance is required, the Batch Credential Endpoint MUST be supported.

JSON Schema for the supported Presentation Definition properties {#presentation-definition-schema}

<{{schemas/presentation_definition.json}}

Acknowledgements {#Acknowledgements}

We would like to thank Paul Bastian, Christian Bormann, Mike Jones, Oliver Terbu, Daniel Fett, and Giuseppe De Marco for their valuable feedback and contributions to this specification.

Notices

Copyright (c) 2023 The OpenID Foundation.

The OpenID Foundation (OIDF) grants to any Contributor, developer, implementer, or other interested party a non-exclusive, royalty free, worldwide copyright license to reproduce, prepare derivative works from, distribute, perform and display, this Implementers Draft or Final Specification solely for the purposes of (i) developing specifications, and (ii) implementing Implementers Drafts and Final Specifications based on such documents, provided that attribution be made to the OIDF as the source of the material, but that such attribution does not indicate an endorsement by the OIDF.

The technology described in this specification was made available from contributions from various sources, including members of the OpenID Foundation and others. Although the OpenID Foundation has taken steps to help ensure that the technology is available for distribution, it takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this specification or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any independent effort to identify any such rights. The OpenID Foundation and the contributors to this specification make no (and hereby expressly disclaim any) warranties (express, implied, or otherwise), including implied warranties of merchantability, non-infringement, fitness for a particular purpose, or title, related to this specification, and the entire risk as to implementing this specification is assumed by the implementer. The OpenID Intellectual Property Rights policy requires contributors to offer a patent promise not to assert certain patent claims against other contributors and against implementers. The OpenID Foundation invites any interested party to bring to its attention any copyrights, patents, patent applications, or other proprietary rights that MAY cover technology that MAY be required to practice this specification.