SD-JWT VC と mdoc の比較｜ウォレットのクレデンシャル形式

import { createHash, generateKeyPairSync, randomBytes, sign } from "node:crypto";
import { SignJWT, exportJWK } from "jose";
import { Encoder, Tag } from "cbor-x";

const sha256 = (b) => createHash("sha256").update(b).digest();
const b64u = (b) => Buffer.from(b).toString("base64url");
const cbor = new Encoder({ useRecords: false, useTag259ForMaps: false, variableMapSize: true, tagUint8Array: false });
const tag24 = (v) => new Tag(cbor.encode(v), 24);

// RFC 9901 §4.2.3 example: digest of the family_name Disclosure
const rfcDisclosure = "WyJfMjZiYzRMVC1hYzZxMktJNmNCVzVlcyIsICJmYW1pbHlfbmFtZSIsICJNw7ZiaXVzIl0";
console.log("RFC 9901 example digest:", b64u(sha256(rfcDisclosure)));

const claims = { given_name: "Erika", family_name: "Mustermann", birth_date: "1984-01-26", age_over_18: true, nationality: "DE" };
const issuer = generateKeyPairSync("ec", { namedCurve: "P-256" });
const holder = generateKeyPairSync("ec", { namedCurve: "P-256" });
const holderJwk = await exportJWK(holder.publicKey);
const nonce = b64u(randomBytes(16));

// SD-JWT VC: one salted Disclosure per claim, their digests signed in _sd
const disclosures = Object.entries(claims).map(([k, v]) => b64u(JSON.stringify([b64u(randomBytes(16)), k, v])));
const jwt = await new SignJWT({
  iss: "https://issuer.example", vct: "https://credentials.example/identity_credential",
  _sd: disclosures.map((d) => b64u(sha256(d))), _sd_alg: "sha-256", cnf: { jwk: holderJwk },
}).setProtectedHeader({ alg: "ES256", typ: "dc+sd-jwt" }).sign(issuer.privateKey);
const issued = `${jwt}~${disclosures.join("~")}~`;
const shown = `${jwt}~${disclosures[3]}~`; // reveal age_over_18 only
const kbJwt = await new SignJWT({ aud: "https://verifier.example", nonce, sd_hash: b64u(sha256(shown)) })
  .setProtectedHeader({ alg: "ES256", typ: "kb+jwt" }).setIssuedAt().sign(holder.privateKey);
console.log(`SD-JWT VC: issued ${issued.length} bytes; presentation of 1 of 5 claims ${(shown + kbJwt).length} bytes`);

// mdoc (ISO/IEC 18013-5): one salted IssuerSignedItem per element, digests signed in the MSO
const ns = "org.iso.18013.5.1";
const docType = "org.iso.18013.5.1.mDL";
const items = Object.entries(claims).map(([k, v], i) =>
  tag24({ digestID: i, random: randomBytes(16), elementIdentifier: k, elementValue: v }));
const coseSign1 = (key, payload, detached) => {
  const prot = cbor.encode(new Map([[1, -7]])); // alg: ES256
  const toBeSigned = cbor.encode(["Signature1", prot, Buffer.alloc(0), payload]);
  return [prot, {}, detached ? null : payload, sign("sha256", toBeSigned, { key, dsaEncoding: "ieee-p1363" })];
};
const mso = {
  version: "1.0", digestAlgorithm: "SHA-256", docType,
  valueDigests: { [ns]: new Map(items.map((t, i) => [i, sha256(cbor.encode(t))])) },
  deviceKeyInfo: { deviceKey: new Map([[1, 2], [-1, 1], [-2, Buffer.from(holderJwk.x, "base64url")], [-3, Buffer.from(holderJwk.y, "base64url")]]) },
  validityInfo: { signed: new Tag("2026-10-20T00:00:00Z", 0), validFrom: new Tag("2026-10-20T00:00:00Z", 0), validUntil: new Tag("2027-10-20T00:00:00Z", 0) },
};
const issuerAuth = coseSign1(issuer.privateKey, cbor.encode(tag24(mso)));
const issuedMdoc = cbor.encode({ nameSpaces: { [ns]: items }, issuerAuth });

// Presentation over OpenID4VP: DeviceResponse signed by the device key over the session transcript
const handoverInfo = cbor.encode(["https://verifier.example", nonce, null, "https://verifier.example/response"]);
const transcript = [null, null, ["OpenID4VPHandover", sha256(handoverInfo)]];
const deviceNameSpaces = tag24({});
const deviceAuth = cbor.encode(tag24(["DeviceAuthentication", transcript, docType, deviceNameSpaces]));
const response = cbor.encode({
  version: "1.0", status: 0,
  documents: [{ docType, issuerSigned: { nameSpaces: { [ns]: [items[3]] }, issuerAuth },
    deviceSigned: { nameSpaces: deviceNameSpaces, deviceAuth: { deviceSignature: coseSign1(holder.privateKey, deviceAuth, true) } } }],
});
console.log(`mdoc:      issued ${issuedMdoc.length} bytes; presentation of 1 of 5 elements ${response.length} bytes (${b64u(response).length} as base64url)`);

RFC 9901 example digest: X9yH0Ajrdm1Oij4tWso9UzzKJvPoDxwmuEcO3XAdRC0
SD-JWT VC: issued 1112 bytes; presentation of 1 of 5 claims 1159 bytes
mdoc:      issued 1046 bytes; presentation of 1 of 5 elements 895 bytes (1194 as base64url)