Flutter - How to generate a private/public key pair to encrypt messages

There is a Dart2 and Flutter compatible pre-release of Pointycastle available.

The default README.md points to the first non-pre-release version and therefore the frontpage shows "DART 2 INCOMPATIBLE", but that only applies to version < 0.11.1.

Just add to pubspec.yaml

dependencies: 
  pointycastle: ^1.0.0-rc4

For examples check the unit tests https://github.com/PointyCastle/pointycastle/blob/master/test/key_generators/rsa_key_generator_test.dart

I started using some sample code for generating public key / private key pair using pointy castles. After a long time of debugging and editing code, I ended up with the following code:

  var keyParams = new RSAKeyGeneratorParameters(BigInt.from(65537), 2048, 5);

  var secureRandom = new FortunaRandom();
  var random = new Random.secure();

  List<int> seeds = [];
  for (int i = 0; i < 32; i++) {
    seeds.add(random.nextInt(255));
  }


  secureRandom.seed(new KeyParameter(new Uint8List.fromList(seeds)));

  var rngParams = new ParametersWithRandom(keyParams, secureRandom);
  var k = new RSAKeyGenerator();
  k.init(rngParams);

  var keyPair = k.generateKeyPair();

  print(new RsaKeyHelper().encodePublicKeyToPem(keyPair.publicKey) );
  print(new RsaKeyHelper().encodePrivateKeyToPem(keyPair.privateKey) );

  AsymmetricKeyParameter<RSAPublicKey> keyParametersPublic = new PublicKeyParameter(keyPair.publicKey);
  var cipher = new RSAEngine()..init(true, keyParametersPublic);

  var cipherText = cipher.process(new Uint8List.fromList("Hello World".codeUnits));

  print("Encrypted: ${new String.fromCharCodes(cipherText)}");

  AsymmetricKeyParameter<RSAPrivateKey> keyParametersPrivate = new PrivateKeyParameter(keyPair.privateKey);

  cipher.init( false, keyParametersPrivate )
  ;
  var decrypted = cipher.process(cipherText);
  print("Decrypted: ${new String.fromCharCodes(decrypted)}");

I used this guy's edits from this git issue page (Look here for some more functions such as encoding to / decoding from PEM