buildProof method

@override FutureOr<Map<String, dynamic>> buildProof(dynamic data, WalletStore wallet, String did, { String? challenge, String? domain, String? proofPurpose, })

Build a LinkedDataProof / DataIntegrityProof

Implementation

@override
FutureOr<Map<String, dynamic>> buildProof(
    data, WalletStore wallet, String did,
    {String? challenge, String? domain, String? proofPurpose}) async {
  var proofOptions = {
    '@context': jsonWebSignature2020ContextIri,
    'type': typeName,
    'proofPurpose': proofPurpose ?? 'assertionMethod',
    'verificationMethod': '$did#${did.split(':')[2]}',
    'created': DateTime.now().toUtc().toIso8601String()
  };
  if (domain != null) {
    proofOptions['domain'] = domain;
  }
  if (challenge != null) {
    proofOptions['challenge'] = challenge;
  }

  List<int> hash = await _dataToHash(data);

  var pOptionsHash = sha256
      .convert(utf8.encode(await JsonLdProcessor.normalize(proofOptions,
          options:
              JsonLdOptions(safeMode: true, documentLoader: loadDocument))))
      .bytes;
  var payload = pOptionsHash + hash;

  String alg;
  Identifier c, a;

  if (did.startsWith('did:key:zQ3s')) {
    c = curves.p256k;
    alg = 'ES256K';
    a = algorithms.signing.ecdsa.sha256;
  } else if (did.startsWith('did:key:z82')) {
    c = curves.p384;
    alg = 'ES384';
    a = algorithms.signing.ecdsa.sha384;
  } else if (did.startsWith('did:key:z2J9')) {
    c = curves.p521;
    alg = 'ES512';
    a = algorithms.signing.ecdsa.sha512;
  } else {
    c = curves.p256;
    alg = 'ES256';
    a = algorithms.signing.ecdsa.sha256;
  }

  var critical = <String, dynamic>{};
  critical['b64'] = false;
  var header = buildJwsHeader(alg: alg, extra: critical);
  var headerEnc = removePaddingFromBase64(header);

  var hashToSign = utf8.encode('$headerEnc.') + payload;

  // proofOptions.remove('@context');

  var privateKeyHex = await wallet.getPrivateKeyForCredentialDid(did);
  privateKeyHex ??= await wallet.getPrivateKeyForConnectionDid(did);
  if (privateKeyHex == null) throw Exception('Could not find a private key');

  var privateKey = EcPrivateKey(
      eccPrivateKey: web3_crypto.hexToInt(privateKeyHex), curve: c);

  var signer = privateKey.createSigner(a);
  var sig = signer.sign(hashToSign);

  proofOptions['jws'] = '$headerEnc.'
      '.${base64UrlEncode(sig.data)}';

  return proofOptions;
}