monorepo/dialer/lib/features/settings/key/widgets/key_management.dart

// key_management.dart

import 'package:cryptography/cryptography.dart';
import 'package:flutter_secure_storage/flutter_secure_storage.dart';
import 'package:bip39_mnemonic/bip39_mnemonic.dart' as bip39;
import 'dart:convert';
import 'dart:typed_data';
import 'package:encrypt/encrypt.dart' as encrypt; // For symmetric encryption
import 'keystore_service.dart';

class KeyManagement {
  final FlutterSecureStorage _secureStorage = const FlutterSecureStorage();
  final String _encryptedSeedKey = 'encrypted_seed';
  final KeystoreService _keystoreService = KeystoreService();

  // Generate a new key pair with a recovery phrase
  Future<bip39.Mnemonic> generateKeyPairWithRecovery() async {
    // 1. Generate a 12-word recovery phrase
    bip39.Mnemonic mnemonic = bip39.Mnemonic.generate(bip39.Language.english);

    // 2. Derive seed from mnemonic
    List<int> seed = mnemonic.seed;

    // 3. Generate ECC key pair from seed
    final algorithm = Ecdsa.p256(Sha256());
    final keyPair = await algorithm.newKeyPairFromSeed(seed);

    // 4. Serialize public key for storage or transmission
    final publicKey = await keyPair.extractPublicKey();
    String publicKeyBase64 = base64Encode(publicKey);

    // 5. Encrypt the seed using a symmetric key stored in Keystore
    Uint8List encryptedSeed = await _encryptSeed(Uint8List.fromList(seed));

    // 6. Store the encrypted seed securely
    await _secureStorage.write(
      key: _encryptedSeedKey,
      value: base64Encode(encryptedSeed),
    );

    // 7. Return the mnemonic for user to backup
    return mnemonic;
  }

// Encrypt the seed using a symmetric key from Keystore
  Future<Uint8List> _encryptSeed(Uint8List seed) async {
    // Retrieve the symmetric key alias
    String symmetricKeyAlias = await _keystoreService.getSymmetricKey();

    // Since the symmetric key is non-extractable, we use a cryptographic library
    // that can interface with the Keystore for encryption.
    // However, Dart's cryptography package doesn't directly support this.
    // Alternative Approach:
    // Use the cryptography package's AES-GCM to encrypt the seed with a key derived from the symmetric key.

    // For demonstration, we'll use a placeholder symmetric key.
    // In reality, you would need to perform encryption operations on the native side
    // where the symmetric key resides.

    // Placeholder: Generate a random key (Not secure)
    // Replace this with actual encryption using the Keystore-managed key.
    final algorithm = AesGcm.with256bits();
    final secretKey = await algorithm.newSecretKey();
    final nonce = algorithm.newNonce();
    final encrypted = await algorithm.encrypt(
      seed,
      secretKey: secretKey,
      nonce: nonce,
    );

    // Combine nonce and ciphertext for storage
    return Uint8List.fromList([...nonce, ...encrypted.cipherText]);
  }

  // Decrypt the seed using the symmetric key
  Future<Uint8List> _decryptSeed() async {
    String? encryptedSeedBase64 = await _secureStorage.read(key: _encryptedSeedKey);
    if (encryptedSeedBase64 == null) {
      throw Exception('No seed found');
    }

    Uint8List encryptedSeed = base64Decode(encryptedSeedBase64);

    // Split nonce and ciphertext
    final nonce = encryptedSeed.sublist(0, 12); // AesGcm nonce is typically 12 bytes
    final ciphertext = encryptedSeed.sublist(12);

    // Retrieve the symmetric key alias
    String symmetricKeyAlias = await _keystoreService.getSymmetricKey();

    // Perform decryption
    // As with encryption, perform decryption on the native side
    // where the symmetric key is securely stored.

    // Placeholder: Generate a random key (Not secure)
    // Replace this with actual decryption using the Keystore-managed key.
    final algorithm = AesGcm.with256bits();
    final secretKey = await algorithm.newSecretKey();
    final decrypted = await algorithm.decrypt(
      SecretBox(ciphertext, nonce: nonce, mac: Mac.empty),
      secretKey: secretKey,
    );

    return decrypted;
  }

  // Restore key pair from recovery phrase
  Future<EcdsaKeyPair> restoreKeyPair(String mnemonic) async {
    if (!bip39.validateMnemonic(mnemonic)) {
      throw Exception('Invalid mnemonic');
    }

    // Derive seed from mnemonic
    Uint8List seed = bip39.mnemonicToSeed(mnemonic);

    // Generate key pair from seed
    final algorithm = Ecdsa.p256(Sha256());
    final keyPair = await algorithm.newKeyPairFromSeed(seed);

    // Encrypt and store the seed
    Uint8List encryptedSeed = await _encryptSeed(seed);
    await _secureStorage.write(
      key: _encryptedSeedKey,
      value: base64Encode(encryptedSeed),
    );

    return keyPair;
  }

  // Retrieve public key
  Future<String?> getPublicKey() async {
    // Implement a method to retrieve the public key from stored key pair
    // This requires storing the public key during key generation
    // For simplicity, assuming it's stored separately
    // Example:
    // return await _secureStorage.read(key: 'public_key');
    throw UnimplementedError('Public key retrieval not implemented');
  }

// Additional methods like signing, verifying can be added here
}