Asymmetric Encryption RSA-AES-CBC with public/private keys using pointycastle lib

pointy_castle_asymmetric_encryption.dart

import 'dart:convert';
import 'dart:math';
import 'dart:typed_data';

import 'package:basic_utils/basic_utils.dart';
import 'package:encrypt/encrypt.dart';
// ignore: depend_on_referenced_packages
import 'package:crypto/crypto.dart';
import 'package:flutter/foundation.dart' as flutter;
import 'package:pointycastle/export.dart';

typedef EncryptionResult = ({
  Uint8List aesEncryptedPayload,
  Uint8List aesKey,
  Uint8List aesIV,
  String? keyChecksum,
});

class AsymmetricEncryption {
  final _RsaAesCbcEncoder _encoder;
  final AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey> _keys;
  final String publicKeyAsPem;
  final String privateKeyAsPem;

  factory AsymmetricEncryption.rsa() {
    final encoder = _RsaAesCbcEncoder();
    final keys = encoder.generateRSAKeyPair();
    final pem = CryptoUtils.encodeRSAPublicKeyToPem(keys.publicKey);
    final privatePem = CryptoUtils.encodeRSAPrivateKeyToPem(keys.privateKey);
    return AsymmetricEncryption(
      keys: keys,
      encoder: encoder,
      publicKeyAsPem: pem,
      privateKeyAsPem: privatePem,
    );
  }

  AsymmetricEncryption({
    required _RsaAesCbcEncoder encoder,
    required AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey> keys,
    required this.publicKeyAsPem,
    required this.privateKeyAsPem,
  })  : _encoder = encoder,
        _keys = keys;

  String encrypt(String data) {
    final req = {
      "encrypt": "aes-cbc-256",
      "publicKey": base64Encode(utf8.encode(publicKeyAsPem)),
      "data": base64Encode(utf8.encode(data)),
    };

    return base64Encode(utf8.encode(jsonEncode(req)));
  }

  String decrypt(String token) {
    final json = utf8.decode(base64Decode(token));
    final res = jsonDecode(json);

    if (res
        case ({
          'publicKeyChecksum': String publicKeyPemCheckSum,
          'key': String aesKey,
          'iv': String aesIV,
          'data': String aesEncryptedPayload,
        })) {
      if (publicKeyPemCheckSum != "SHA256:${sha256.convert(utf8.encode(publicKeyAsPem))}") {
        throw 'invalid pubic key checksum';
      }
      return _encoder.decryptAesCbc(
        (
          aesKey: base64.decode(aesKey),
          aesEncryptedPayload: base64.decode(aesEncryptedPayload),
          aesIV: base64.decode(aesIV),
          keyChecksum: publicKeyPemCheckSum,
        ),
        _keys,
      );
    }
    throw "invalid json input";
  }
}

class _RsaAesCbcEncoder {
  Uint8List decryptRsa(Uint8List data, AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey> pair) {
    final algo = RSA(
      publicKey: pair.publicKey,
      privateKey: pair.privateKey,
      encoding: RSAEncoding.OAEP,
    );
    final encrypter = Encrypter(algo);
    final res = encrypter.decryptBytes(Encrypted(data));
    assert(res.length == 32);
    return Uint8List.fromList(res);
  }

  String decryptAesCbc(EncryptionResult res, AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey> pair) {
    final aesKey = decryptRsa(res.aesKey, pair);
    final encrypter = Encrypter(AES(Key(aesKey), mode: AESMode.cbc));
    return encrypter.decrypt(Encrypted(res.aesEncryptedPayload), iv: IV(res.aesIV));
  }

  AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey> generateRSAKeyPair() {
    if (flutter.kIsWeb) {
      return AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey>(
        CryptoUtils.rsaPublicKeyFromPemPkcs1(_publicKeyPem),
        CryptoUtils.rsaPrivateKeyFromPemPkcs1(_privateKeyPem),
      );
    }

    final randomSeed = Uint8List.fromList(List<int>.generate(32, (i) => i));
    final rsaKeyGenerator = RSAKeyGeneratorParameters(BigInt.from(flutter.kIsWeb ? 15 : 65537), 4096, 64);
    final randomGenerator = FortunaRandom()..seed(KeyParameter(randomSeed));

    final keyGen = RSAKeyGenerator()
      ..init(
        ParametersWithRandom(
          rsaKeyGenerator,
          randomGenerator,
        ),
      );

    final pair = keyGen.generateKeyPair();
    final myPublic = pair.publicKey as RSAPublicKey;
    final myPrivate = pair.privateKey as RSAPrivateKey;

    return AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey>(myPublic, myPrivate);
  }

  String generatebase64RandomKey({int length = 32}) {
    final random = Random.secure();
    final items = List<int>.generate(length, (i) => random.nextInt(256));
    return base64.encode(items);
  }
}

final _privateKeyPem = '''-----BEGIN RSA PRIVATE KEY-----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ner3lnqKAseXHpV8pGVTnlNVLRd9KrWFb19i9fmpshOs1a6yE18bFJ6YI3VtK1LK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3rku/d/oW2741xQdIvhLDC8BtxxwIpD/D2gGpTOM11/hknFvpDg1zfnxX6k=
-----END RSA PRIVATE KEY-----''';

final _publicKeyPem = '''-----BEGIN RSA PUBLIC KEY-----
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
-----END RSA PUBLIC KEY-----''';