refactor: Clean up the X3DH implementation

lib/src/x3dh/x3dh.dart

@@ -1,125 +0,0 @@
-import 'dart:convert';
-import 'dart:typed_data';
-import 'package:cryptography/cryptography.dart';
-import 'package:pinenacl/api.dart';
-import 'package:pinenacl/tweetnacl.dart';
-
-/// The overarching assumption is that we use Ed25519 keys for the identity keys
-
-class X3DHRun {
-
-  const X3DHRun(this.epk, this.sharedSecret);
-  final SimpleKeyPair epk;
-  final List<int> sharedSecret;
-}
-
-SimpleKeyPairData fromPublicKey(SimplePublicKey pk) {
-  return SimpleKeyPairData([], publicKey: pk, type: KeyPairType.x25519);
-}
-
-Future<List<int>> sig(SimpleKeyPair keyPair, List<int> message) async {
-  final signature = await Ed25519().sign(
-    message,
-    keyPair: keyPair,
-  );
-
-  return signature.bytes;
-}
-
-/// Performs X25519 with [pk1] and [pk2]. If [identityKey] is set, then
-/// it indicates which of [pk1] ([identityKey] == 1) or [pk2] ([identityKey] == 2)
-/// is the identity key.
-Future<List<int>> dh(SimpleKeyPair kp, SimplePublicKey pk, int identityKey) async {
-  var ckp = kp;
-  var cpk = pk;
-
-  if (identityKey == 1) {
-    final pubkeyBytes = (await kp.extractPublicKey()).bytes;
-    final pkc = Uint8List(32);
-    TweetNaClExt.crypto_sign_ed25519_pk_to_x25519_pk(pkc, Uint8List.fromList(pubkeyBytes));
-
-    final keyPairData = await kp.extract();
-    final privateKeyBytes = await keyPairData.extractPrivateKeyBytes();
-    final skc = Uint8List(32);
-    TweetNaClExt.crypto_sign_ed25519_sk_to_x25519_sk(skc, Uint8List.fromList(privateKeyBytes));
-
-    ckp = SimpleKeyPairData(
-      List<int>.from(skc),
-      publicKey: SimplePublicKey(List<int>.from(pkc), type: KeyPairType.x25519),
-      type: KeyPairType.x25519,
-    );
-  } else if (identityKey == 2) {
-    final pubkeyBytes = pk.bytes;
-    final pkc = Uint8List(32);
-    TweetNaClExt.crypto_sign_ed25519_pk_to_x25519_pk(pkc, Uint8List.fromList(pubkeyBytes));
-
-    cpk = SimplePublicKey(
-      List<int>.from(pkc),
-      type: KeyPairType.x25519,
-    );
-  }
-
-  final shared = await Cryptography.instance.x25519().sharedSecretKey(
-    keyPair: ckp,
-    remotePublicKey: cpk,
-  );
-
-  return shared.extractBytes();
-}
-
-Future<List<int>> kdf(List<int> km) async {
-  final f = List<int>.filled(32, 0xFF);
-  final input = List<int>.empty(growable: true);
-  input
-    ..addAll(f)
-    ..addAll(km);
-
-  final algorithm = Hkdf(
-    hmac: Hmac(Sha256()),
-    outputLength: 32,
-  );
-  final output = await algorithm.deriveKey(
-    secretKey: SecretKey(input),
-    // TODO: Fix
-    nonce: List<int>.filled(32, 0x00),
-    info: utf8.encode('OMEMO X3DH'),
-  );
-
-  return output.extractBytes();
-}
-
-List<int> concat(List<List<int>> inputs) {
-  final tmp = List<int>.empty(growable: true);
-  for (final input in inputs) {
-    tmp.addAll(input);
-  }
-
-  return tmp;
-}
-
-// Alice -> Bob
-Future<X3DHRun> x3dhFromPrekeyBundle(SimplePublicKey ikb, SimplePublicKey spkb, SimplePublicKey opkb, SimpleKeyPair ika) async {
-  // Generate EPK
-  final epk = await Cryptography.instance.x25519().newKeyPair();
-
-  final dh1 = await dh(ika, spkb, 1);
-  final dh2 = await dh(epk, ikb,  2);
-  final dh3 = await dh(epk, spkb, 0);
-  final dh4 = await dh(epk, opkb, 0);
-
-  final sk = await kdf(concat([dh1, dh2, dh3, dh4]));
-
-  return X3DHRun(
-    epk,
-    sk,
-  );
-}
-
-Future<List<int>> x3dhFromInitialMessage(SimplePublicKey ika, SimplePublicKey epk, SimpleKeyPair opkb, SimpleKeyPair spk, SimpleKeyPair ikb) async {
-  final dh1 = await dh(spk, ika, 2);
-  final dh2 = await dh(ikb, epk, 1);
-  final dh3 = await dh(spk, epk, 0);
-  final dh4 = await dh(opkb, epk, 0);
-
-  return kdf(concat([dh1, dh2, dh3, dh4]));
-}