OpenID4VC High Assurance Interoperability Profile with SD-JWT VC - draft 01

Table of Contents

1. 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).¶

2. Terminology

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

3. 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¶

4. 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 Section 7.2.¶
• 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.¶

{
  "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",
  }
}

5. OpenID for Verifiable Presentations

• MUST support protocol extensions for SD-JWT VC credential format profile as defined in this specification Section 7.2.¶
• 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 Appendix B:¶

  • 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 (pickonly), count, from properties MUST be supported.¶

6. 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¶

7. SD-JWT VCs

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)¶

• 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 Section 7.1.¶
• 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.¶

8. 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¶

9. Implementations Considerations

Appendix A. Combined Issuance of SD-JWT VC and mdocs

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

Appendix B. JSON Schema for the supported Presentation Definition properties

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "Presentation Definition for a High Assurance Profile",
    "type": "object",
    "properties": {
      "presentation_definition": {
        "$ref": "#/definitions/presentation_definition"
      }
    },
    "definitions": {
      "presentation_definition": {
        "type": "object",
        "properties": {
          "id": {
            "type": "string"
          },
          "input_descriptors": {
            "type": "array",
            "items": {
              "$ref": "#/definitions/input_descriptor"
            }
          },
          "submission_requirements": {
            "type": "array",
            "items": {
              "$ref": "#/definitions/submission_requirement"
            }
          }
        },
        "required": [
          "id",
          "input_descriptors"
        ],
        "additionalProperties": false
      },
      "input_descriptor": {
        "type": "object",
        "additionalProperties": false,
        "properties": {
          "id": {
            "type": "string"
          },
          "name": {
            "type": "string"
          },
          "purpose": {
            "type": "string"
          },
          "format": {
            "$ref": "http://identity.foundation/claim-format-registry/schemas/presentation-definition-claim-format-designations.json"
          },
          "group": {
            "type": "array",
            "items": {
              "type": "string"
            }
          },
          "constraints": {
            "type": "object",
            "additionalProperties": false,
            "properties": {
              "limit_disclosure": {
                "type": "string",
                "enum": [
                  "required",
                  "preferred"
                ]
              },
              "fields": {
                "type": "array",
                "items": {
                  "path": {
                    "type": "array",
                    "items": {
                      "type": "string"
                    }
                  },
                  "filter": {
                    "$ref": "http://json-schema.org/draft-07/schema#"
                  }
                }
              }
            }
          }
        },
        "required": [
          "id",
          "constraints"
        ]
      },
      "submission_requirement": {
        "type": "object",
        "oneOf": [
          {
            "properties": {
              "name": {
                "type": "string"
              },
              "rule": {
                "type": "string",
                "enum": [
                  "pick"
                ]
              },
              "count": {
                "type": "integer",
                "minimum": 1
              },
              "from": {
                "type": "string"
              }
            },
            "required": [
              "rule",
              "from"
            ],
            "additionalProperties": false
          }
        ]
      }
    }
  }

Appendix C. 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.¶

Appendix D. 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.¶

Authors' Addresses