fix: Make decryption work

lib/omemo_dart.dart

@@ -5,4 +5,5 @@ export 'src/errors.dart';
 export 'src/helpers.dart';
 export 'src/keys.dart';
 export 'src/omemo/bundle.dart';
+export 'src/omemo/sessionmanager.dart';
 export 'src/x3dh/x3dh.dart';

lib/src/omemo/sessionmanager.dart

@@ -5,6 +5,7 @@ import 'package:omemo_dart/src/crypto.dart';
 import 'package:omemo_dart/src/double_ratchet/double_ratchet.dart';
 import 'package:omemo_dart/src/errors.dart';
 import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/omemo/bundle.dart';
 import 'package:omemo_dart/src/omemo/device.dart';
 import 'package:synchronized/synchronized.dart';
 
@@ -36,6 +37,7 @@ class OmemoSessionManager {
 
   /// Generate a new cryptographic identity.
   static Future<OmemoSessionManager> generateNewIdentity({ int opkAmount = 100 }) async {
+    assert(opkAmount > 0, 'opkAmount must be bigger than 0.');
     final device = await Device.generateNewDevice(opkAmount: opkAmount);
 
     return OmemoSessionManager(device);
@@ -73,6 +75,10 @@ class OmemoSessionManager {
     });
   }
 
+  Future<void> addSessionFromBundle(String jid, String deviceId, OmemoBundle bundle) async {
+    // TODO(PapaTutuWawa): Do
+  }
+  
   /// Encrypt the key [plaintext] for all known bundles of [jid]. Returns a map that
   /// maps the Bundle Id to the ciphertext of [plaintext].
   Future<EncryptionResult> encryptToJid(String jid, String plaintext) async {
@@ -87,7 +93,7 @@ class OmemoSessionManager {
       keys.iv,
     );
     final hmac = await truncatedHmac(ciphertext, keys.authenticationKey);
-    final concatKey = concat([keys.encryptionKey, hmac]);
+    final concatKey = concat([key, hmac]);
 
     await _lock.synchronized(() async {
       // We assume that the user already checked if the session exists
@@ -127,7 +133,7 @@ class OmemoSessionManager {
     final message = OMEMOMessage.fromBuffer(authMessage.message);
     
     final ratchet = _ratchetMap[senderDeviceId]!;
-    final keyAndHmac = await ratchet.ratchetDecrypt(message, message.ciphertext);
+    final keyAndHmac = await ratchet.ratchetDecrypt(message, decodedRawKey);
     final key = keyAndHmac.sublist(0, 32);
     final hmac = keyAndHmac.sublist(32, 48);
     final derivedKeys = await deriveEncryptionKeys(key, omemoPayloadInfoString);

test/omemo_test.dart

@@ -0,0 +1,69 @@
+import 'dart:convert';
+import 'package:omemo_dart/omemo_dart.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('Test using OMEMO sessions with only one device per user', () async {
+    const aliceJid = 'alice@server.example';
+    const bobJid = 'bob@other.server.example';
+      
+    // Alice and Bob generate their sessions
+    final aliceSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
+    final bobSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
+
+    // Perform the X3DH
+    final x3dhAliceResult = await x3dhFromBundle(
+      await bobSession.device.toBundle(),
+      aliceSession.device.ik,
+    );
+    final x3dhBobResult = await x3dhFromInitialMessage(
+      X3DHMessage(
+        aliceSession.device.ik.pk,
+        x3dhAliceResult.ek.pk,
+        '2',
+      ),
+      bobSession.device.spk,
+      bobSession.device.opks.values.elementAt(0),
+      bobSession.device.ik,
+    );
+
+    // Build the ratchets
+    final aliceRatchet = await OmemoDoubleRatchet.initiateNewSession(
+      bobSession.device.spk.pk,
+      x3dhAliceResult.sk,
+      x3dhAliceResult.ad,
+    );
+    final bobRatchet = await OmemoDoubleRatchet.acceptNewSession(
+      bobSession.device.spk,
+      x3dhBobResult.sk,
+      x3dhBobResult.ad,
+    );
+
+    // Add the ratchets to the session managers
+    await aliceSession.addSession(bobJid, bobSession.device.id, aliceRatchet);
+    await bobSession.addSession(aliceJid, aliceSession.device.id, bobRatchet);
+
+    // Alice encrypts a message for Bob
+    const messagePlaintext = 'Hello Bob!';
+    final aliceMessage = await aliceSession.encryptToJid(bobJid, messagePlaintext);
+    expect(aliceMessage.encryptedKeys.length, 1);
+
+    // Alice sends the message to Bob
+    // ...
+
+    // Bob decrypts it
+    final bobMessage = await bobSession.decryptMessage(
+      aliceMessage.ciphertext,
+      aliceJid,
+      aliceSession.device.id,
+      [
+        EncryptedKey(
+          bobSession.device.id,
+          base64.encode(aliceMessage.encryptedKeys[bobSession.device.id]!),
+        ),
+      ],
+    );
+
+    expect(messagePlaintext, bobMessage);
+  });
+}