appe2ee.dart

	    import 'dart:typed_data';
	    import 'package:shared_preferences/shared_preferences.dart';
	    import 'package:webcrypto/webcrypto.dart';
	    class AppE2EE {
	      static final AppE2EE 
	    = AppE2EE._internal();
	      factory AppE2EE() {
	        return 
	    ;
	      }
	      AppE2EE._internal();
	      KeyPair<EcdhPrivateKey, EcdhPublicKey> keyPair;
	      Uint8List derivedBits;
	      AesGcmSecretKey aesGcmSecretKey;
	      final Uint8List iv = Uint8List.fromList('Initialization Vector'.codeUnits);
	      Future<void> generateKeys() async {
	        final prefs = await SharedPreferences.
	    ();
	        String derivedBitsString = (prefs.getString('derivedBits') ?? '');
	        if (derivedBitsString.isNotEmpty) {
	          derivedBits = Uint8List.fromList(derivedBitsString.codeUnits);
	          print('derivedBits present');
	          return;
	        }
	        // 1. Generate keys
	        keyPair = await EcdhPrivateKey.
	    (EllipticCurve.p256);
	        Map<String, dynamic> publicKeyJwk =
	            await keyPair.publicKey.exportJsonWebKey();
	        Map<String, dynamic> privateKeyJwk =
	            await keyPair.privateKey.exportJsonWebKey();
	        print('keypair $keyPair, $publicKeyJwk, $privateKeyJwk');
	        deriveBits();
	      }
	      Future<void> deriveBits() async {
	        // 2. Derive bits
	        derivedBits = await keyPair.privateKey.deriveBits(256, keyPair.publicKey);
	        final prefs = await SharedPreferences.
	    ();
	        prefs.setString('derivedBits', String.fromCharCodes(derivedBits));
	        print('derivedBits $derivedBits');
	      }
	      Future<String> encrypt(String message) async {
	        // 3. Encrypt
	        aesGcmSecretKey = await AesGcmSecretKey.
	    (derivedBits);
	        List<int> list = message.codeUnits;
	        Uint8List data = Uint8List.fromList(list);
	        Uint8List encryptedBytes = await aesGcmSecretKey.encryptBytes(data, iv);
	        String encryptedString = String.fromCharCodes(encryptedBytes);
	        print('encryptedString $encryptedString');
	        return encryptedString;
	      }
	      Future<String> decrypt(String encryptedMessage) async {
	        // 4. Decrypt
	        aesGcmSecretKey = await AesGcmSecretKey.
	    (derivedBits);
	        List<int> message = Uint8List.fromList(encryptedMessage.codeUnits);
	        Uint8List decryptdBytes = await aesGcmSecretKey.decryptBytes(message, iv);
	        String decryptdString = String.fromCharCodes(decryptdBytes);
	        print('decryptdString $decryptdString');
	        return decryptdString;
	      }
	    }