add experimental passkey utils

lib/src/soroban/soroban_passkey.dart

@@ -0,0 +1,205 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:stellar_flutter_sdk/src/key_pair.dart';
+import 'package:stellar_flutter_sdk/src/network.dart';
+import 'package:stellar_flutter_sdk/src/util.dart';
+import 'package:stellar_flutter_sdk/src/xdr/xdr_contract.dart';
+import 'package:stellar_flutter_sdk/src/xdr/xdr_data_io.dart';
+import 'package:stellar_flutter_sdk/src/xdr/xdr_transaction.dart';
+import 'package:stellar_flutter_sdk/src/xdr/xdr_type.dart';
+
+class PasskeyUtils {
+
+  /// Extracts the public key from the authenticator attestation [response] received
+  /// from the webauthn registration.
+  static Uint8List? getPublicKey(AuthenticatorAttestationResponse response) {
+    final publicKeyStr = response.publicKey;
+
+    Uint8List? publicKey = publicKeyStr != null
+        ? base64Url.decode(base64Url.normalize(publicKeyStr))
+        : null;
+
+    if (publicKey == null ||
+        publicKey.isEmpty ||
+        publicKey.first != 0x04 ||
+        publicKey.length != 65) {
+      // see https://www.w3.org/TR/webauthn/#attestation-object
+      final authenticatorDataStr = response.authenticatorData;
+      if (authenticatorDataStr != null) {
+        Uint8List authData =
+            base64Url.decode(base64Url.normalize(authenticatorDataStr));
+        // Get credentialIdLength, which is at offset 53 (and is big-endian)
+        final credentialIdLength = (authData[53] << 8) + authData[54];
+        final x =
+            authData.sublist(65 + credentialIdLength, 97 + credentialIdLength);
+        final y = authData.sublist(
+            100 + credentialIdLength, 132 + credentialIdLength);
+        return Uint8List.fromList([
+          [0x04],
+          x,
+          y
+        ].expand((x) => x).toList());
+      }
+
+      final attestationObjectStr = response.attestationObject;
+      if (attestationObjectStr != null) {
+        Uint8List attestationObject =
+            base64Url.decode(base64Url.normalize(attestationObjectStr));
+        final publicKeyPrefixSlice = Uint8List.fromList(
+            [0xa5, 0x01, 0x02, 0x03, 0x26, 0x20, 0x01, 0x21, 0x58, 0x20]);
+        var startIndex =
+            attestationObject.indexOfElements(publicKeyPrefixSlice);
+        if (startIndex != -1) {
+          startIndex = startIndex + publicKeyPrefixSlice.length;
+          final x = attestationObject.sublist(startIndex, 32 + startIndex);
+          final y = attestationObject.sublist(35 + startIndex, 67 + startIndex);
+          return Uint8List.fromList([
+            [0x04],
+            x,
+            y
+          ].expand((x) => x).toList());
+        }
+      }
+    }
+    return publicKey;
+  }
+
+  /// Generates the webauthn (account) contract salt from the webauthn registration response credentials id or
+  /// authentication response credentials id.
+  static Uint8List getContractSalt(String credentialsId) {
+    return Util.hash(base64Url.decode(base64Url.normalize(credentialsId)));
+  }
+
+  /// Derives a contract id of the webauthn (account) contract that will be created from the [contractSalt],
+  /// the contract id: [factoryContractId] of the factory contract that will be used to deploy the webauthn (account) contract
+  /// and the stellar [network] where the webauthn and factory contracts are operation.
+  static String deriveContractId(
+      {required Uint8List contractSalt,
+      required String factoryContractId,
+      required Network network}) {
+    final preimage =
+        XdrHashIDPreimage(XdrEnvelopeType.ENVELOPE_TYPE_CONTRACT_ID);
+    final contractIdPreimage = XdrContractIDPreimage(
+        XdrContractIDPreimageType.CONTRACT_ID_PREIMAGE_FROM_ADDRESS);
+    contractIdPreimage.address = XdrSCAddress.forContractId(factoryContractId);
+    contractIdPreimage.salt = XdrUint256(contractSalt);
+    final preimageCID = XdrHashIDPreimageContractID(
+        XdrHash(network.networkId!), contractIdPreimage);
+    preimage.contractID = preimageCID;
+    XdrDataOutputStream xdrOutputStream = XdrDataOutputStream();
+    XdrHashIDPreimage.encode(xdrOutputStream, preimage);
+    return StrKey.encodeContractId(
+        Util.hash(Uint8List.fromList(xdrOutputStream.bytes)));
+  }
+
+  /// Convert EcdsaSignatureAsn [signature] received from the webauthn authentication
+  /// to compact. The resulting compact signature is to be used as authentication
+  /// signature for the webauthn (account) contract __checkAuth invocation.
+  static Uint8List compactSignature(Uint8List signature) {
+    // Decode the DER signature
+    var offset = 2;
+    final rLength = signature[offset + 1];
+    final r = signature.sublist(offset + 2, offset + 2 + rLength);
+
+    offset += 2 + rLength;
+
+    final sLength = signature[offset + 1];
+    final s = signature.sublist(offset + 2, offset + 2 + sLength);
+
+    // Convert r and s to BigInt
+    final rHexStr = Util.bytesToHex(r);
+    final sHexStr = Util.bytesToHex(s);
+    final rBigInt = BigInt.parse('0x$rHexStr');
+    var sBigInt = BigInt.parse('0x$sHexStr');
+
+    // Ensure s is in the low-S form
+    // https://github.com/stellar/stellar-protocol/discussions/1435#discussioncomment-8809175
+    // https://discord.com/channels/897514728459468821/1233048618571927693
+    // Define the order of the curve secp256r1
+    // https://github.com/RustCrypto/elliptic-curves/blob/master/p256/src/lib.rs#L72
+    final BigInt n = BigInt.parse('0xffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551');
+    final BigInt halfN = n ~/ BigInt.from(2);
+
+    if (sBigInt > halfN) {
+      sBigInt = n - sBigInt;
+    }
+
+    // Convert back to buffers and ensure they are 32 bytes
+    final rPadded = rBigInt.toRadixString(16).padLeft(64, '0');
+    final sLowS = sBigInt.toRadixString(16).padLeft(64, '0');
+    final rPaddedBytes = Util.hexToBytes(rPadded);
+    final sLowSBytes = Util.hexToBytes(sLowS);
+
+    // Concatenate r and low-s
+    var b = BytesBuilder();
+    b.add(rPaddedBytes);
+    b.add(sLowSBytes);
+
+    final concatSignature = b.toBytes();
+    return concatSignature;
+  }
+}
+
+/// https://w3c.github.io/webauthn/#dictdef-authenticatorattestationresponsejson
+class AuthenticatorAttestationResponse {
+  String? clientDataJSON;
+  String? authenticatorData;
+  String? attestationObject;
+  List<String>? transports;
+  String? publicKey;
+
+  /// Constructor for AuthenticatorAttestationResponse.
+  AuthenticatorAttestationResponse({
+    this.clientDataJSON,
+    this.authenticatorData,
+    this.attestationObject,
+    this.transports,
+    this.publicKey,
+  });
+
+  /// Construct AuthenticatorAttestationResponse from JSON.
+  factory AuthenticatorAttestationResponse.fromJson(Map<String, dynamic> json) {
+    return AuthenticatorAttestationResponse(
+      clientDataJSON: json['clientDataJSON'],
+      attestationObject: json['attestationObject'],
+      authenticatorData: json['authenticatorData'],
+      publicKey: json['publicKey'],
+      transports: json['transports'] != null
+          ? List<String>.from(json['transports'])
+          : null,
+    );
+  }
+
+  /// Convert Response to JSON.
+  Map<String, dynamic> toJson() {
+    return {
+      'clientDataJSON': clientDataJSON,
+      'authenticatorData': authenticatorData,
+      'attestationObject': attestationObject,
+      'transports': transports,
+      'publicKey': publicKey,
+    };
+  }
+}
+
+extension IndexOfElements<T> on List<T> {
+  int indexOfElements(List<T> elements, [int start = 0]) {
+    if (elements.isEmpty) return start;
+    var end = length - elements.length;
+    if (start > end) return -1;
+    var first = elements.first;
+    var pos = start;
+    while (true) {
+      pos = indexOf(first, pos);
+      if (pos < 0 || pos > end) return -1;
+      for (var i = 1; i < elements.length; i++) {
+        if (this[pos + i] != elements[i]) {
+          pos++;
+          continue;
+        }
+      }
+      return pos;
+    }
+  }
+}

lib/stellar_flutter_sdk.dart

@@ -187,4 +187,5 @@ export 'src/sep/0008/regulated_assets.dart';
 /// Soroban
 export 'src/soroban/soroban_server.dart';
 export 'src/soroban/soroban_auth.dart';
-export 'src/soroban/soroban_contract_parser.dart';
+export 'src/soroban/soroban_contract_parser.dart';
+export 'src/soroban/soroban_passkey.dart';