CHANGELOG.md

@@ -54,15 +54,3 @@
 ## 0.4.3
 
 - Fix bug that causes ratchets to be unable to decrypt anything after receiving a heartbeat with a completely new session
-
-## 0.5.0
-
-This version is a complete rework of omemo_dart!
-
-- Removed events from `OmemoManager`
-- Removed `OmemoSessionManager`
-- Removed serialization/deserialization code
-- Replace exceptions with errors inside a result type
-- Ratchets and trust data is now loaded and cached on demand
-- Accessing the trust manager must happen via `withTrustManager`
-- Overriding the base implementations is replaced by providing callback functions

README.md

@@ -28,33 +28,23 @@ Include `omemo_dart` in your `pubspec.yaml` like this:
 dependencies:
   omemo_dart:
     hosted: https://git.polynom.me/api/packages/PapaTutuWawa/pub
-    version: ^0.5.0
+    version: ^0.4.3
   # [...]
 
 # [...]
 ```
 
-### Example
-
-This repository includes a documented ["example"](./example/omemo_dart_example.dart) that explains the basic usage of the library while
-leaving out the XMPP specific bits. For a more functional and integrated example, see the `omemo_client.dart` example from
-[moxxmpp](https://codeberg.org/moxxy/moxxmpp).
-
-### Persistence
-
-By default, `omemo_dart` uses in-memory implementations for everything. For a real-world application, this is unsuitable as OMEMO devices would be constantly added.
-In order to allow persistence, your application needs to keep track of the following:
-
-- The `OmemoDevice` assigned to the `OmemoManager`
-- `JID -> [int]`: The device list for each JID
-- `(JID, device) -> Ratchet`: The actual ratchet
-
-If you also use the `BlindTrustBeforeVerificationTrustManager`, you additionally need to keep track of:
-
-- `(JID, device) -> (int, bool)`: The trust level and the enablement state
-
 ## Contributing
 
+Due to issues with `protobuf`, `omemo_dart` reimplements the Protobuf encoding for the required
+OMEMO messages. As such, `protobuf` is only a dependency for testing that the serialisation and
+deserialisation of the custom implementation. In order to run tests, you need the Protbuf
+compiler. After that, making sure that
+the [Dart Protobuf compiler addon](https://pub.dev/packages/protoc_plugin) and the
+Protobuf compiler itself is in your PATH,
+run `protoc -I=./protobuf/ --dart_out=lib/protobuf/ ./protobuf/schema.proto` in the
+repository's root to generate the real Protobuf bindings.
+
 When submitting a PR, please run the linter using `dart analyze` and make sure that all
 tests still pass using `dart test`.
 

analysis_options.yaml

@@ -9,5 +9,8 @@ linter:
 
 analyzer:
   exclude:
-    - "lib/src/protobuf/*.dart"
+    - "lib/protobuf/*.dart"
+    # TODO: Remove once OmemoSessionManager is gone
+    - "test/omemo_test.dart"
     - "example/omemo_dart_example.dart"
+    - "test/serialisation_test.dart"

example/omemo_dart_example.dart

@@ -35,10 +35,6 @@ void main() async {
     // This needs to be wired into your XMPP library's OMEMO implementation.
     // For simplicity, we use an empty function and imagine it works.
     (jid) async {},
-    // This function is called whenever our own device bundle has to be republished to our PEP node.
-    // This needs to be wired into your XMPP library's OMEMO implementation.
-    // For simplicity, we use an empty function and imagine it works.
-    (device) async {},
   );
 
   // Alice now wants to chat with Bob at his bare Jid "bob@other.server". To make things
@@ -46,7 +42,7 @@ void main() async {
   // request it using PEP and then convert the device bundle into a OmemoBundle object.
   final bobManager = OmemoManager(
     await OmemoDevice.generateNewDevice(bobJid),
-    BlindTrustBeforeVerificationTrustManager(),
+    MemoryBTBVTrustManager(),
     (result, recipient) async => {},
     (jid) async => [],
     (jid, id) async => null,
@@ -149,11 +145,6 @@ void main() async {
       /// The text of the <payload /> element, if it exists. If not, then the message might be
       /// a hearbeat, where no payload is sent. In that case, use null.
       payload,
-
-      /// Since we did not receive this message due to a catch-up mechanism, like MAM, we
-      /// set this to false. If we, however, did use a catch-up mechanism, we must set this
-      /// to true to prevent the OPKs from being replaced.
-      false,
     ),
   );
 

lib/omemo_dart.dart

@@ -8,10 +8,9 @@ export 'src/omemo/bundle.dart';
 export 'src/omemo/device.dart';
 export 'src/omemo/encrypted_key.dart';
 export 'src/omemo/encryption_result.dart';
-export 'src/omemo/errors.dart';
+export 'src/omemo/events.dart';
 export 'src/omemo/fingerprint.dart';
-export 'src/omemo/omemo.dart';
-export 'src/omemo/ratchet_data.dart';
+export 'src/omemo/omemomanager.dart';
 export 'src/omemo/ratchet_map_key.dart';
 export 'src/omemo/stanza.dart';
 export 'src/trust/base.dart';

lib/src/common/constants.dart

@@ -1,11 +0,0 @@
-/// The overarching assumption is that we use Ed25519 keys for the identity keys
-const omemoX3DHInfoString = 'OMEMO X3DH';
-
-/// The info used for when encrypting the AES key for the actual payload.
-const omemoPayloadInfoString = 'OMEMO Payload';
-
-/// Info string for ENCRYPT
-const encryptHkdfInfoString = 'OMEMO Message Key Material';
-
-/// Amount of messages we may skip per session
-const maxSkip = 1000;

lib/src/crypto.dart

@@ -1,7 +1,5 @@
 import 'dart:convert';
 import 'package:cryptography/cryptography.dart';
-import 'package:moxlib/moxlib.dart';
-import 'package:omemo_dart/src/errors.dart';
 import 'package:omemo_dart/src/keys.dart';
 
 /// Performs X25519 with [kp] and [pk]. If [identityKey] is set, then
@@ -94,7 +92,7 @@ Future<List<int>> aes256CbcEncrypt(
 
 /// A small helper function to make AES-256-CBC easier. Decrypt [ciphertext] using [key] as
 /// the encryption key and [iv] as the IV. Returns the ciphertext.
-Future<Result<MalformedCiphertextError, List<int>>> aes256CbcDecrypt(
+Future<List<int>> aes256CbcDecrypt(
   List<int> ciphertext,
   List<int> key,
   List<int> iv,
@@ -102,19 +100,13 @@ Future<Result<MalformedCiphertextError, List<int>>> aes256CbcDecrypt(
   final algorithm = AesCbc.with256bits(
     macAlgorithm: MacAlgorithm.empty,
   );
-  try {
-    return Result(
-      await algorithm.decrypt(
-        NoMacSecretBox(
-          ciphertext,
-          nonce: iv,
-        ),
-        secretKey: SecretKey(key),
-      ),
-    );
-  } catch (ex) {
-    return Result(MalformedCiphertextError(ex));
-  }
+  return algorithm.decrypt(
+    NoMacSecretBox(
+      ciphertext,
+      nonce: iv,
+    ),
+    secretKey: SecretKey(key),
+  );
 }
 
 /// OMEMO often uses the output of a HMAC-SHA-256 truncated to its first 16 bytes.

lib/src/double_ratchet/crypto.dart

@@ -0,0 +1,60 @@
+import 'package:omemo_dart/src/crypto.dart';
+import 'package:omemo_dart/src/errors.dart';
+import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/protobuf/omemo_authenticated_message.dart';
+import 'package:omemo_dart/src/protobuf/omemo_message.dart';
+
+/// Info string for ENCRYPT
+const encryptHkdfInfoString = 'OMEMO Message Key Material';
+
+/// Signals ENCRYPT function as specified by OMEMO 0.8.3.
+/// Encrypt [plaintext] using the message key [mk], given associated_data [associatedData]
+/// and the AD output from the X3DH [sessionAd].
+Future<List<int>> encrypt(
+  List<int> mk,
+  List<int> plaintext,
+  List<int> associatedData,
+  List<int> sessionAd,
+) async {
+  // Generate encryption, authentication key and IV
+  final keys = await deriveEncryptionKeys(mk, encryptHkdfInfoString);
+  final ciphertext =
+      await aes256CbcEncrypt(plaintext, keys.encryptionKey, keys.iv);
+
+  final header =
+      OmemoMessage.fromBuffer(associatedData.sublist(sessionAd.length))
+        ..ciphertext = ciphertext;
+  final headerBytes = header.writeToBuffer();
+  final hmacInput = concat([sessionAd, headerBytes]);
+  final hmacResult = await truncatedHmac(hmacInput, keys.authenticationKey);
+  final message = OmemoAuthenticatedMessage()
+    ..mac = hmacResult
+    ..message = headerBytes;
+  return message.writeToBuffer();
+}
+
+/// Signals DECRYPT function as specified by OMEMO 0.8.3.
+/// Decrypt [ciphertext] with the message key [mk], given the associated_data [associatedData]
+/// and the AD output from the X3DH.
+Future<List<int>> decrypt(
+  List<int> mk,
+  List<int> ciphertext,
+  List<int> associatedData,
+  List<int> sessionAd,
+) async {
+  // Generate encryption, authentication key and IV
+  final keys = await deriveEncryptionKeys(mk, encryptHkdfInfoString);
+
+  // Assumption ciphertext is a OMEMOAuthenticatedMessage
+  final message = OmemoAuthenticatedMessage.fromBuffer(ciphertext);
+  final header = OmemoMessage.fromBuffer(message.message!);
+
+  final hmacInput = concat([sessionAd, header.writeToBuffer()]);
+  final hmacResult = await truncatedHmac(hmacInput, keys.authenticationKey);
+
+  if (!listsEqual(hmacResult, message.mac!)) {
+    throw InvalidMessageHMACException();
+  }
+
+  return aes256CbcDecrypt(header.ciphertext!, keys.encryptionKey, keys.iv);
+}

lib/src/double_ratchet/double_ratchet.dart

@@ -1,25 +1,48 @@
+import 'dart:convert';
 import 'package:cryptography/cryptography.dart';
 import 'package:hex/hex.dart';
 import 'package:meta/meta.dart';
-import 'package:moxlib/moxlib.dart';
-import 'package:omemo_dart/src/common/constants.dart';
 import 'package:omemo_dart/src/crypto.dart';
+import 'package:omemo_dart/src/double_ratchet/crypto.dart';
 import 'package:omemo_dart/src/double_ratchet/kdf.dart';
 import 'package:omemo_dart/src/errors.dart';
 import 'package:omemo_dart/src/helpers.dart';
 import 'package:omemo_dart/src/keys.dart';
-import 'package:omemo_dart/src/protobuf/schema.pb.dart';
+import 'package:omemo_dart/src/protobuf/omemo_message.dart';
+
+/// Amount of messages we may skip per session
+const maxSkip = 1000;
+
+class RatchetStep {
+  const RatchetStep(this.header, this.ciphertext);
+  final OmemoMessage header;
+  final List<int> ciphertext;
+}
 
 @immutable
 class SkippedKey {
   const SkippedKey(this.dh, this.n);
 
-  /// The DH public key for which we skipped a message key.
-  final OmemoPublicKey dh;
+  factory SkippedKey.fromJson(Map<String, dynamic> data) {
+    return SkippedKey(
+      OmemoPublicKey.fromBytes(
+        base64.decode(data['public']! as String),
+        KeyPairType.x25519,
+      ),
+      data['n']! as int,
+    );
+  }
 
-  /// The associated number of the message key we skipped.
+  final OmemoPublicKey dh;
   final int n;
 
+  Future<Map<String, dynamic>> toJson() async {
+    return {
+      'public': base64.encode(await dh.getBytes()),
+      'n': n,
+    };
+  }
+
   @override
   bool operator ==(Object other) {
     return other is SkippedKey && other.dh == dh && other.n == n;
@@ -29,28 +52,6 @@ class SkippedKey {
   int get hashCode => dh.hashCode ^ n.hashCode;
 }
 
-@immutable
-class KeyExchangeData {
-  const KeyExchangeData(
-    this.pkId,
-    this.spkId,
-    this.ik,
-    this.ek,
-  );
-
-  /// The id of the used OPK.
-  final int pkId;
-
-  /// The id of the used SPK.
-  final int spkId;
-
-  /// The ephemeral key used while the key exchange.
-  final OmemoPublicKey ek;
-
-  /// The identity key used in the key exchange.
-  final OmemoPublicKey ik;
-}
-
 class OmemoDoubleRatchet {
   OmemoDoubleRatchet(
     this.dhs, // DHs
@@ -65,9 +66,77 @@ class OmemoDoubleRatchet {
     this.sessionAd,
     this.mkSkipped, // MKSKIPPED
     this.acknowledged,
+    this.kexTimestamp,
     this.kex,
   );
 
+  factory OmemoDoubleRatchet.fromJson(Map<String, dynamic> data) {
+    /*
+    {
+      'dhs': 'base/64/encoded',
+      'dhs_pub': 'base/64/encoded',
+      'dhr': null | 'base/64/encoded',
+      'rk': 'base/64/encoded',
+      'cks': null | 'base/64/encoded',
+      'ckr': null | 'base/64/encoded',
+      'ns': 0,
+      'nr': 0,
+      'pn': 0,
+      'ik_pub': null | 'base/64/encoded',
+      'session_ad': 'base/64/encoded',
+      'acknowledged': true | false,
+      'kex_timestamp': int,
+      'kex': 'base/64/encoded',
+      'mkskipped': [
+        {
+          'key': 'base/64/encoded',
+          'public': 'base/64/encoded',
+          'n': 0
+        }, ...
+      ]
+    }
+    */
+    // NOTE: Dart has some issues with just casting a List<dynamic> to List<Map<...>>, as
+    //       such we need to convert the items by hand.
+    final mkSkipped = Map<SkippedKey, List<int>>.fromEntries(
+      (data['mkskipped']! as List<dynamic>)
+          .map<MapEntry<SkippedKey, List<int>>>(
+        (entry) {
+          final map = entry as Map<String, dynamic>;
+          final key = SkippedKey.fromJson(map);
+          return MapEntry(
+            key,
+            base64.decode(map['key']! as String),
+          );
+        },
+      ),
+    );
+
+    return OmemoDoubleRatchet(
+      OmemoKeyPair.fromBytes(
+        base64.decode(data['dhs_pub']! as String),
+        base64.decode(data['dhs']! as String),
+        KeyPairType.x25519,
+      ),
+      decodeKeyIfNotNull(data, 'dhr', KeyPairType.x25519),
+      base64.decode(data['rk']! as String),
+      base64DecodeIfNotNull(data, 'cks'),
+      base64DecodeIfNotNull(data, 'ckr'),
+      data['ns']! as int,
+      data['nr']! as int,
+      data['pn']! as int,
+      OmemoPublicKey.fromBytes(
+        base64.decode(data['ik_pub']! as String),
+        KeyPairType.ed25519,
+      ),
+      base64.decode(data['session_ad']! as String),
+      mkSkipped,
+      data['acknowledged']! as bool,
+      data['kex_timestamp']! as int,
+      data['kex'] as String?,
+    );
+  }
+
   /// Sending DH keypair
   OmemoKeyPair dhs;
 
@@ -92,14 +161,16 @@ class OmemoDoubleRatchet {
   /// for verification purposes
   final OmemoPublicKey ik;
 
-  /// Associated data for this ratchet.
   final List<int> sessionAd;
 
-  /// List of skipped message keys.
   final Map<SkippedKey, List<int>> mkSkipped;
 
+  /// The point in time at which we performed the kex exchange to create this ratchet.
+  /// Precision is milliseconds since epoch.
+  int kexTimestamp;
+
   /// The key exchange that was used for initiating the session.
-  final KeyExchangeData kex;
+  final String? kex;
 
   /// Indicates whether we received an empty OMEMO message after building a session with
   /// the device.
@@ -110,22 +181,21 @@ class OmemoDoubleRatchet {
   /// a X3DH. [ik] refers to Bob's (the receiver's) IK public key.
   static Future<OmemoDoubleRatchet> initiateNewSession(
     OmemoPublicKey spk,
-    int spkId,
     OmemoPublicKey ik,
-    OmemoPublicKey ownIk,
-    OmemoPublicKey ek,
     List<int> sk,
     List<int> ad,
-    int pkId,
+    int timestamp,
   ) async {
     final dhs = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
-    final rk = await kdfRk(sk, await omemoDH(dhs, spk, 0));
+    final dhr = spk;
+    final rk = await kdfRk(sk, await omemoDH(dhs, dhr, 0));
+    final cks = rk;
 
     return OmemoDoubleRatchet(
       dhs,
-      spk,
-      List.from(rk),
-      List.from(rk),
+      dhr,
+      rk,
+      cks,
       null,
       0,
       0,
@@ -134,12 +204,8 @@ class OmemoDoubleRatchet {
       ad,
       {},
       false,
-      KeyExchangeData(
-        pkId,
-        spkId,
-        ownIk,
-        ek,
-      ),
+      timestamp,
+      '',
     );
   }
 
@@ -149,12 +215,10 @@ class OmemoDoubleRatchet {
   /// Alice's (the initiator's) IK public key.
   static Future<OmemoDoubleRatchet> acceptNewSession(
     OmemoKeyPair spk,
-    int spkId,
     OmemoPublicKey ik,
-    int pkId,
-    OmemoPublicKey ek,
     List<int> sk,
     List<int> ad,
+    int kexTimestamp,
   ) async {
     return OmemoDoubleRatchet(
       spk,
@@ -169,52 +233,72 @@ class OmemoDoubleRatchet {
       ad,
       {},
       true,
-      KeyExchangeData(
-        pkId,
-        spkId,
-        ik,
-        ek,
-      ),
+      kexTimestamp,
+      null,
     );
   }
 
-  /// Performs a single ratchet step in case we received a new
-  /// public key in [header].
-  Future<void> _dhRatchet(OMEMOMessage header) async {
-    pn = ns;
-    ns = 0;
-    nr = 0;
-    dhr = OmemoPublicKey.fromBytes(header.dhPub, KeyPairType.x25519);
-    final newRk1 = await kdfRk(
-      rk,
-      await omemoDH(
-        dhs,
-        dhr!,
-        0,
-      ),
-    );
-    rk = List.from(newRk1);
-    ckr = List.from(newRk1);
+  Future<Map<String, dynamic>> toJson() async {
+    final mkSkippedSerialised =
+        List<Map<String, dynamic>>.empty(growable: true);
+    for (final entry in mkSkipped.entries) {
+      final result = await entry.key.toJson();
+      result['key'] = base64.encode(entry.value);
 
-    dhs = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
-    final newRk2 = await kdfRk(
-      rk,
-      await omemoDH(
-        dhs,
-        dhr!,
-        0,
-      ),
-    );
-    rk = List.from(newRk2);
-    cks = List.from(newRk2);
+      mkSkippedSerialised.add(result);
+    }
+
+    return {
+      'dhs': base64.encode(await dhs.sk.getBytes()),
+      'dhs_pub': base64.encode(await dhs.pk.getBytes()),
+      'dhr': dhr != null ? base64.encode(await dhr!.getBytes()) : null,
+      'rk': base64.encode(rk),
+      'cks': cks != null ? base64.encode(cks!) : null,
+      'ckr': ckr != null ? base64.encode(ckr!) : null,
+      'ns': ns,
+      'nr': nr,
+      'pn': pn,
+      'ik_pub': base64.encode(await ik.getBytes()),
+      'session_ad': base64.encode(sessionAd),
+      'mkskipped': mkSkippedSerialised,
+      'acknowledged': acknowledged,
+      'kex_timestamp': kexTimestamp,
+      'kex': kex,
+    };
   }
 
-  /// Skip (and keep track of) message keys until our receive counter is
-  /// equal to [until]. If we would skip too many messages, returns
-  /// a [SkippingTooManyKeysError]. If not, returns null.
-  Future<OmemoError?> _skipMessageKeys(int until) async {
+  /// Returns the OMEMO compatible fingerprint of the ratchet session.
+  Future<String> getOmemoFingerprint() async {
+    final curveKey = await ik.toCurve25519();
+    return HEX.encode(await curveKey.getBytes());
+  }
+
+  Future<List<int>?> _trySkippedMessageKeys(
+    OmemoMessage header,
+    List<int> ciphertext,
+  ) async {
+    final key = SkippedKey(
+      OmemoPublicKey.fromBytes(header.dhPub!, KeyPairType.x25519),
+      header.n!,
+    );
+    if (mkSkipped.containsKey(key)) {
+      final mk = mkSkipped[key]!;
+      mkSkipped.remove(key);
+
+      return decrypt(
+        mk,
+        ciphertext,
+        concat([sessionAd, header.writeToBuffer()]),
+        sessionAd,
+      );
+    }
+
+    return null;
+  }
+
+  Future<void> _skipMessageKeys(int until) async {
     if (nr + maxSkip < until) {
-      return SkippingTooManyKeysError();
+      throw SkippingTooManyMessagesException();
     }
 
     if (ckr != null) {
@@ -222,140 +306,88 @@ class OmemoDoubleRatchet {
         final newCkr = await kdfCk(ckr!, kdfCkNextChainKey);
         final mk = await kdfCk(ckr!, kdfCkNextMessageKey);
         ckr = newCkr;
-
         mkSkipped[SkippedKey(dhr!, nr)] = mk;
         nr++;
       }
     }
-
-    return null;
   }
 
-  /// Decrypt [ciphertext] using keys derived from the message key [mk]. Also computes the
-  /// HMAC from the [OMEMOMessage] embedded in [message].
-  ///
-  /// If the computed HMAC does not match the HMAC in [message], returns
-  /// [InvalidMessageHMACError]. If it matches, returns the decrypted
-  /// payload.
-  Future<Result<OmemoError, List<int>>> _decrypt(
-    OMEMOAuthenticatedMessage message,
-    List<int> ciphertext,
-    List<int> mk,
-  ) async {
-    final keys = await deriveEncryptionKeys(mk, encryptHkdfInfoString);
+  Future<void> _dhRatchet(OmemoMessage header) async {
+    pn = ns;
+    ns = 0;
+    nr = 0;
+    dhr = OmemoPublicKey.fromBytes(header.dhPub!, KeyPairType.x25519);
 
-    final hmacInput = concat([sessionAd, message.message]);
-    final hmacResult = await truncatedHmac(hmacInput, keys.authenticationKey);
-    if (!listsEqual(hmacResult, message.mac)) {
-      return Result(InvalidMessageHMACError());
-    }
-
-    final plaintext =
-        await aes256CbcDecrypt(ciphertext, keys.encryptionKey, keys.iv);
-    if (plaintext.isType<MalformedCiphertextError>()) {
-      return Result(plaintext.get<MalformedCiphertextError>());
-    }
-
-    return Result(plaintext.get<List<int>>());
+    final newRk = await kdfRk(rk, await omemoDH(dhs, dhr!, 0));
+    rk = List.from(newRk);
+    ckr = List.from(newRk);
+    dhs = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
+    final newNewRk = await kdfRk(rk, await omemoDH(dhs, dhr!, 0));
+    rk = List.from(newNewRk);
+    cks = List.from(newNewRk);
   }
 
-  /// Checks whether we could decrypt the payload in [header] with a skipped key. If yes,
-  /// attempts to decrypt it. If not, returns null.
-  ///
-  /// If the decryption is successful, returns the plaintext payload. If an error occurs, like
-  /// an [InvalidMessageHMACError], that is returned instead.
-  Future<Result<OmemoError, List<int>?>> _trySkippedMessageKeys(
-    OMEMOAuthenticatedMessage message,
-    OMEMOMessage header,
-  ) async {
-    final key = SkippedKey(
-      OmemoPublicKey.fromBytes(header.dhPub, KeyPairType.x25519),
-      header.n,
+  /// Encrypt [plaintext] using the Double Ratchet.
+  Future<RatchetStep> ratchetEncrypt(List<int> plaintext) async {
+    final newCks = await kdfCk(cks!, kdfCkNextChainKey);
+    final mk = await kdfCk(cks!, kdfCkNextMessageKey);
+
+    cks = newCks;
+    final header = OmemoMessage()
+      ..dhPub = await dhs.pk.getBytes()
+      ..pn = pn
+      ..n = ns;
+
+    ns++;
+
+    return RatchetStep(
+      header,
+      await encrypt(
+        mk,
+        plaintext,
+        concat([sessionAd, header.writeToBuffer()]),
+        sessionAd,
+      ),
     );
-    if (mkSkipped.containsKey(key)) {
-      final mk = mkSkipped[key]!;
-      mkSkipped.remove(key);
-
-      return _decrypt(message, header.ciphertext, mk);
-    }
-
-    return const Result(null);
   }
 
-  /// Decrypt the payload (deeply) embedded in [message].
+  /// Decrypt a [ciphertext] that was sent with the header [header] using the Double
+  /// Ratchet. Returns the decrypted (raw) plaintext.
   ///
-  /// If everything goes well, returns the plaintext payload. If an error occurs, that
-  /// is returned instead.
-  Future<Result<OmemoError, List<int>>> ratchetDecrypt(
-    OMEMOAuthenticatedMessage message,
+  /// Throws an SkippingTooManyMessagesException if too many messages were to be skipped.
+  Future<List<int>> ratchetDecrypt(
+    OmemoMessage header,
+    List<int> ciphertext,
   ) async {
-    final header = OMEMOMessage.fromBuffer(message.message);
-
-    // Try skipped keys
-    final plaintextRaw = await _trySkippedMessageKeys(message, header);
-    if (plaintextRaw.isType<OmemoError>()) {
-      // Propagate the error
-      return Result(plaintextRaw.get<OmemoError>());
-    }
-
-    final plaintext = plaintextRaw.get<List<int>?>();
+    // Check if we skipped too many messages
+    final plaintext = await _trySkippedMessageKeys(header, ciphertext);
     if (plaintext != null) {
-      return Result(plaintext);
+      return plaintext;
     }
 
-    if (dhr == null || !listsEqual(header.dhPub, await dhr!.getBytes())) {
-      final skipResult1 = await _skipMessageKeys(header.pn);
-      if (skipResult1 != null) {
-        return Result(skipResult1);
-      }
-
+    final dhPubMatches = listsEqual(
+      header.dhPub!,
+      (await dhr?.getBytes()) ?? <int>[],
+    );
+    if (!dhPubMatches) {
+      await _skipMessageKeys(header.pn!);
       await _dhRatchet(header);
     }
 
-    final skipResult2 = await _skipMessageKeys(header.n);
-    if (skipResult2 != null) {
-      return Result(skipResult2);
-    }
-
-    final ck = await kdfCk(ckr!, kdfCkNextChainKey);
+    await _skipMessageKeys(header.n!);
+    final newCkr = await kdfCk(ckr!, kdfCkNextChainKey);
     final mk = await kdfCk(ckr!, kdfCkNextMessageKey);
-    ckr = ck;
+    ckr = newCkr;
     nr++;
 
-    return _decrypt(message, header.ciphertext, mk);
+    return decrypt(
+      mk,
+      ciphertext,
+      concat([sessionAd, header.writeToBuffer()]),
+      sessionAd,
+    );
   }
 
-  /// Encrypt the payload [plaintext] using the double ratchet session.
-  Future<OMEMOAuthenticatedMessage> ratchetEncrypt(List<int> plaintext) async {
-    // Advance the ratchet
-    final ck = await kdfCk(cks!, kdfCkNextChainKey);
-    final mk = await kdfCk(cks!, kdfCkNextMessageKey);
-    cks = ck;
-
-    // Generate encryption, authentication key and IV
-    final keys = await deriveEncryptionKeys(mk, encryptHkdfInfoString);
-    final ciphertext =
-        await aes256CbcEncrypt(plaintext, keys.encryptionKey, keys.iv);
-
-    // Fill-in the header and serialize it here so we do it only once
-    final header = OMEMOMessage()
-      ..dhPub = await dhs.pk.getBytes()
-      ..pn = pn
-      ..n = ns
-      ..ciphertext = ciphertext;
-    final headerBytes = header.writeToBuffer();
-
-    // Increment the send counter
-    ns++;
-
-    final newAd = concat([sessionAd, headerBytes]);
-    final hmac = await truncatedHmac(newAd, keys.authenticationKey);
-    return OMEMOAuthenticatedMessage()
-      ..mac = hmac
-      ..message = headerBytes;
-  }
-
-  /// Returns a copy of the ratchet.
   OmemoDoubleRatchet clone() {
     return OmemoDoubleRatchet(
       dhs,
@@ -370,16 +402,27 @@ class OmemoDoubleRatchet {
       sessionAd,
       Map<SkippedKey, List<int>>.from(mkSkipped),
       acknowledged,
+      kexTimestamp,
       kex,
     );
   }
 
-  /// Computes the fingerprint of the double ratchet, according to
-  /// XEP-0384.
-  Future<String> get fingerprint async {
-    final curveKey = await ik.toCurve25519();
-    return HEX.encode(
-      await curveKey.getBytes(),
+  OmemoDoubleRatchet cloneWithKex(String kex) {
+    return OmemoDoubleRatchet(
+      dhs,
+      dhr,
+      rk,
+      cks != null ? List<int>.from(cks!) : null,
+      ckr != null ? List<int>.from(ckr!) : null,
+      ns,
+      nr,
+      pn,
+      ik,
+      sessionAd,
+      Map<SkippedKey, List<int>>.from(mkSkipped),
+      acknowledged,
+      kexTimestamp,
+      kex,
     );
   }
 
@@ -411,6 +454,7 @@ class OmemoDoubleRatchet {
         ns == other.ns &&
         nr == other.nr &&
         pn == other.pn &&
-        listsEqual(sessionAd, other.sessionAd);
+        listsEqual(sessionAd, other.sessionAd) &&
+        kexTimestamp == other.kexTimestamp;
   }
 }

lib/src/double_ratchet/kdf.dart

@@ -8,7 +8,7 @@ const kdfRkInfoString = 'OMEMO Root Chain';
 const kdfCkNextMessageKey = 0x01;
 const kdfCkNextChainKey = 0x02;
 
-/// Signals KDF_CK function as specified by OMEMO 0.8.3.
+/// Signals KDF_CK function as specified by OMEMO 0.8.0.
 Future<List<int>> kdfCk(List<int> ck, int constant) async {
   final hkdf = Hkdf(hmac: Hmac(Sha256()), outputLength: 32);
   final result = await hkdf.deriveKey(
@@ -19,7 +19,7 @@ Future<List<int>> kdfCk(List<int> ck, int constant) async {
   return result.extractBytes();
 }
 
-/// Signals KDF_RK function as specified by OMEMO 0.8.3.
+/// Signals KDF_RK function as specified by OMEMO 0.8.0.
 Future<List<int>> kdfRk(List<int> rk, List<int> dhOut) async {
   final algorithm = Hkdf(
     hmac: Hmac(Sha256()),

lib/src/errors.dart

@@ -1,39 +1,61 @@
-abstract class OmemoError {}
+abstract class OmemoException {}
 
 /// Triggered during X3DH if the signature if the SPK does verify to the actual SPK.
-class InvalidKeyExchangeSignatureError extends OmemoError {}
+class InvalidSignatureException extends OmemoException implements Exception {
+  String errMsg() =>
+      'The signature of the SPK does not match the provided signature';
+}
 
 /// Triggered by the Double Ratchet if the computed HMAC does not match the attached HMAC.
-class InvalidMessageHMACError extends OmemoError {}
+/// Triggered by the Session Manager if the computed HMAC does not match the attached HMAC.
+class InvalidMessageHMACException extends OmemoException implements Exception {
+  String errMsg() => 'The computed HMAC does not match the provided HMAC';
+}
 
 /// Triggered by the Double Ratchet if skipping messages would cause skipping more than
 /// MAXSKIP messages
-class SkippingTooManyKeysError extends OmemoError {}
+class SkippingTooManyMessagesException extends OmemoException
+    implements Exception {
+  String errMsg() => 'Skipping messages would cause a skip bigger than MAXSKIP';
+}
 
 /// Triggered by the Session Manager if the message key is not encrypted for the device.
-class NotEncryptedForDeviceError extends OmemoError {}
+class NotEncryptedForDeviceException extends OmemoException
+    implements Exception {
+  String errMsg() => 'Not encrypted for this device';
+}
+
+/// Triggered by the Session Manager when there is no key for decrypting the message.
+class NoDecryptionKeyException extends OmemoException implements Exception {
+  String errMsg() => 'No key available for decrypting the message';
+}
 
 /// Triggered by the Session Manager when the identifier of the used Signed Prekey
 /// is neither the current SPK's identifier nor the old one's.
-class UnknownSignedPrekeyError extends OmemoError {}
+class UnknownSignedPrekeyException extends OmemoException implements Exception {
+  String errMsg() => 'Unknown Signed Prekey used.';
+}
+
+/// Triggered by the Session Manager when the received Key Exchange message does not meet
+/// the requirement that a key exchange, given that the ratchet already exists, must be
+/// sent after its creation.
+class InvalidKeyExchangeException extends OmemoException implements Exception {
+  String errMsg() => 'The key exchange was sent before the last kex finished';
+}
+
+/// Triggered by the Session Manager when a message's sequence number is smaller than we
+/// expect it to be.
+class MessageAlreadyDecryptedException extends OmemoException
+    implements Exception {
+  String errMsg() => 'The message has already been decrypted';
+}
 
 /// Triggered by the OmemoManager when we could not encrypt a message as we have
 /// no key material available. That happens, for example, when we want to create a
 /// ratchet session with a JID we had no session with but fetching the device bundle
 /// failed.
-class NoKeyMaterialAvailableError extends OmemoError {}
-
-/// A non-key-exchange message was received that was encrypted for our device, but we have no ratchet with
-/// the device that sent the message.
-class NoSessionWithDeviceError extends OmemoError {}
-
-/// Caused when the AES-256 CBC decryption failed.
-class MalformedCiphertextError extends OmemoError {
-  MalformedCiphertextError(this.ex);
-
-  /// The exception that was raised while decryption.
-  final Object ex;
+class NoKeyMaterialAvailableException extends OmemoException
+    implements Exception {
+  String errMsg() =>
+      'No key material available to create a ratchet session with';
 }
-
-/// Caused by an empty <key /> element
-class MalformedEncryptedKeyError extends OmemoError {}

lib/src/helpers.dart

@@ -1,5 +1,7 @@
 import 'dart:convert';
 import 'dart:math';
+import 'package:cryptography/cryptography.dart';
+import 'package:omemo_dart/src/keys.dart';
 
 /// Flattens [inputs] and concatenates the elements.
 List<int> concat(List<List<int>> inputs) {
@@ -41,35 +43,41 @@ int generateRandom32BitNumber() {
   return Random.secure().nextInt(4294967295 /*pow(2, 32) - 1*/);
 }
 
-/// Describes the differences between two lists in terms of its items.
-class ListDiff<T> {
-  ListDiff(this.added, this.removed);
+OmemoPublicKey? decodeKeyIfNotNull(
+  Map<String, dynamic> map,
+  String key,
+  KeyPairType type,
+) {
+  if (map[key] == null) return null;
 
-  /// The items that were added.
-  final List<T> added;
-
-  /// The items that were removed.
-  final List<T> removed;
+  return OmemoPublicKey.fromBytes(
+    base64.decode(map[key]! as String),
+    type,
+  );
 }
 
-extension AppendToListOrCreateExtension<K, V> on Map<K, List<V>> {
-  /// Create or append [value] to the list identified with key [key].
-  void appendOrCreate(K key, V value, {bool checkExistence = false}) {
-    if (containsKey(key)) {
-      if (!checkExistence) {
-        this[key]!.add(value);
-      }
-      if (!this[key]!.contains(value)) {
-        this[key]!.add(value);
-      }
-    } else {
-      this[key] = [value];
-    }
-  }
+List<int>? base64DecodeIfNotNull(Map<String, dynamic> map, String key) {
+  if (map[key] == null) return null;
+
+  return base64.decode(map[key]! as String);
 }
 
-extension StringFromBase64Extension on String {
-  /// Base64-decode this string. Useful for doing `someString?.fromBase64()` instead
-  /// of `someString != null ? base64Decode(someString) : null`.
-  List<int> fromBase64() => base64Decode(this);
+String? base64EncodeIfNotNull(List<int>? bytes) {
+  if (bytes == null) return null;
+
+  return base64.encode(bytes);
+}
+
+OmemoKeyPair? decodeKeyPairIfNotNull(String? pk, String? sk, KeyPairType type) {
+  if (pk == null || sk == null) return null;
+
+  return OmemoKeyPair.fromBytes(
+    base64.decode(pk),
+    base64.decode(sk),
+    type,
+  );
+}
+
+int getTimestamp() {
+  return DateTime.now().millisecondsSinceEpoch;
 }

lib/src/omemo/constants.dart

@@ -0,0 +1,2 @@
+/// The info used for when encrypting the AES key for the actual payload.
+const omemoPayloadInfoString = 'OMEMO Payload';

lib/src/omemo/decryption_result.dart

@@ -3,15 +3,7 @@ import 'package:omemo_dart/src/errors.dart';
 
 @immutable
 class DecryptionResult {
-  const DecryptionResult(this.payload, this.usedOpkId, this.error);
-
-  /// The decrypted payload or null, if it was an empty OMEMO message.
+  const DecryptionResult(this.payload, this.error);
   final String? payload;
-
-  /// In case a key exchange has been performed: The id of the used OPK. Useful for
-  /// replacing the OPK after a message catch-up.
-  final int? usedOpkId;
-
-  /// The error that occurred during decryption or null, if no error occurred.
-  final OmemoError? error;
+  final OmemoException? error;
 }

lib/src/omemo/device.dart

@@ -22,6 +22,76 @@ class OmemoDevice {
     this.opks,
   );
 
+  /// Deserialize the Device
+  factory OmemoDevice.fromJson(Map<String, dynamic> data) {
+    // NOTE: We use the way OpenSSH names their keys, meaning that ik is the Identity
+    //       Keypair's private key, while ik_pub refers to the Identity Keypair's public
+    //       key.
+    /*
+    {
+      'jid': 'alice@...',
+      'id': 123,
+      'ik': 'base/64/encoded',
+      'ik_pub': 'base/64/encoded',
+      'spk': 'base/64/encoded',
+      'spk_pub': 'base/64/encoded',
+      'spk_id': 123,
+      'spk_sig': 'base/64/encoded',
+      'old_spk': 'base/64/encoded',
+      'old_spk_pub': 'base/64/encoded',
+      'old_spk_id': 122,
+      'opks': [
+        {
+          'id': 0,
+          'public': 'base/64/encoded',
+          'private': 'base/64/encoded'
+        }, ...
+      ]
+    }
+    */
+    // NOTE: Dart has some issues with just casting a List<dynamic> to List<Map<...>>, as
+    //       such we need to convert the items by hand.
+    final opks = Map<int, OmemoKeyPair>.fromEntries(
+      (data['opks']! as List<dynamic>).map<MapEntry<int, OmemoKeyPair>>(
+        (opk) {
+          final map = opk as Map<String, dynamic>;
+          return MapEntry(
+            map['id']! as int,
+            OmemoKeyPair.fromBytes(
+              base64.decode(map['public']! as String),
+              base64.decode(map['private']! as String),
+              KeyPairType.x25519,
+            ),
+          );
+        },
+      ),
+    );
+
+    return OmemoDevice(
+      data['jid']! as String,
+      data['id']! as int,
+      OmemoKeyPair.fromBytes(
+        base64.decode(data['ik_pub']! as String),
+        base64.decode(data['ik']! as String),
+        KeyPairType.ed25519,
+      ),
+      OmemoKeyPair.fromBytes(
+        base64.decode(data['spk_pub']! as String),
+        base64.decode(data['spk']! as String),
+        KeyPairType.x25519,
+      ),
+      data['spk_id']! as int,
+      base64.decode(data['spk_sig']! as String),
+      decodeKeyPairIfNotNull(
+        data['old_spk_pub'] as String?,
+        data['old_spk'] as String?,
+        KeyPairType.x25519,
+      ),
+      data['old_spk_id'] as int?,
+      opks,
+    );
+  }
+
   /// Generate a completely new device, i.e. cryptographic identity.
   static Future<OmemoDevice> generateNewDevice(
     String jid, {
@@ -35,16 +105,7 @@ class OmemoDevice {
 
     final opks = <int, OmemoKeyPair>{};
     for (var i = 0; i < opkAmount; i++) {
-      // Generate unique ids for each key
-      while (true) {
-        final opkId = generateRandom32BitNumber();
-        if (opks.containsKey(opkId)) {
-          continue;
-        }
-
-        opks[opkId] = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
-        break;
-      }
+      opks[i] = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
     }
 
     return OmemoDevice(jid, id, ik, spk, spkId, signature, null, null, opks);
@@ -81,18 +142,7 @@ class OmemoDevice {
   /// a new Device object that copies over everything but replaces said key.
   @internal
   Future<OmemoDevice> replaceOnetimePrekey(int id) async {
-    opks.remove(id);
-
-    // Generate a new unique id for the OPK.
-    while (true) {
-      final newId = generateRandom32BitNumber();
-      if (opks.containsKey(newId)) {
-        continue;
-      }
-
-      opks[newId] = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
-      break;
-    }
+    opks[id] = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
 
     return OmemoDevice(
       jid,
@@ -171,6 +221,34 @@ class OmemoDevice {
     return HEX.encode(await curveKey.getBytes());
   }
 
+  /// Serialise the device information.
+  Future<Map<String, dynamic>> toJson() async {
+    /// Serialise the OPKs
+    final serialisedOpks = List<Map<String, dynamic>>.empty(growable: true);
+    for (final entry in opks.entries) {
+      serialisedOpks.add({
+        'id': entry.key,
+        'public': base64.encode(await entry.value.pk.getBytes()),
+        'private': base64.encode(await entry.value.sk.getBytes()),
+      });
+    }
+
+    return {
+      'jid': jid,
+      'id': id,
+      'ik': base64.encode(await ik.sk.getBytes()),
+      'ik_pub': base64.encode(await ik.pk.getBytes()),
+      'spk': base64.encode(await spk.sk.getBytes()),
+      'spk_pub': base64.encode(await spk.pk.getBytes()),
+      'spk_id': spkId,
+      'spk_sig': base64.encode(spkSignature),
+      'old_spk': base64EncodeIfNotNull(await oldSpk?.sk.getBytes()),
+      'old_spk_pub': base64EncodeIfNotNull(await oldSpk?.pk.getBytes()),
+      'old_spk_id': oldSpkId,
+      'opks': serialisedOpks,
+    };
+  }
+
   @visibleForTesting
   Future<bool> equals(OmemoDevice other) async {
     var opksMatch = true;

lib/src/omemo/encrypted_key.dart

@@ -1,23 +1,12 @@
-import 'dart:convert';
-
 import 'package:meta/meta.dart';
 
 /// EncryptedKey is the intermediary format of a <key /> element in the OMEMO message's
 /// <keys /> header.
 @immutable
 class EncryptedKey {
-  const EncryptedKey(this.rid, this.value, this.kex);
-
-  /// The id of the device the key is encrypted for.
+  const EncryptedKey(this.jid, this.rid, this.value, this.kex);
+  final String jid;
   final int rid;
-
-  /// The base64-encoded payload.
   final String value;
-
-  /// Flag indicating whether the payload is a OMEMOKeyExchange (true) or
-  /// an OMEMOAuthenticatedMessage (false).
   final bool kex;
-
-  /// The base64-decoded payload.
-  List<int> get data => base64Decode(value);
 }

lib/src/omemo/encryption_result.dart

@@ -1,6 +1,7 @@
 import 'package:meta/meta.dart';
+import 'package:omemo_dart/src/errors.dart';
 import 'package:omemo_dart/src/omemo/encrypted_key.dart';
-import 'package:omemo_dart/src/omemo/errors.dart';
+import 'package:omemo_dart/src/omemo/ratchet_map_key.dart';
 
 @immutable
 class EncryptionResult {
@@ -8,7 +9,7 @@ class EncryptionResult {
     this.ciphertext,
     this.encryptedKeys,
     this.deviceEncryptionErrors,
-    this.canSend,
+    this.jidEncryptionErrors,
   );
 
   /// The actual message that was encrypted.
@@ -16,12 +17,17 @@ class EncryptionResult {
 
   /// Mapping of the device Id to the key for decrypting ciphertext, encrypted
   /// for the ratchet with said device Id.
-  final Map<String, List<EncryptedKey>> encryptedKeys;
+  final List<EncryptedKey> encryptedKeys;
 
-  /// Mapping of a JID to
-  final Map<String, List<EncryptToJidError>> deviceEncryptionErrors;
+  /// Mapping of a ratchet map keys to a possible exception.
+  final Map<RatchetMapKey, OmemoException> deviceEncryptionErrors;
 
-  /// A flag indicating that the message could be sent like that, i.e. we were able
-  /// to encrypt to at-least one device per recipient.
-  final bool canSend;
+  /// Mapping of a JID to a possible exception.
+  final Map<String, OmemoException> jidEncryptionErrors;
+
+  /// True if the encryption was a success. This means that we could encrypt for
+  /// at least one ratchet.
+  bool isSuccess(int numberOfRecipients) =>
+      encryptedKeys.isNotEmpty &&
+      jidEncryptionErrors.length < numberOfRecipients;
 }

lib/src/omemo/errors.dart

@@ -1,12 +0,0 @@
-import 'package:omemo_dart/src/errors.dart';
-
-/// Returned on encryption, if encryption failed for some reason.
-class EncryptToJidError extends OmemoError {
-  EncryptToJidError(this.device, this.error);
-
-  /// The device the error occurred with
-  final int? device;
-
-  /// The actual error.
-  final OmemoError error;
-}

lib/src/omemo/events.dart

@@ -0,0 +1,44 @@
+import 'package:omemo_dart/src/double_ratchet/double_ratchet.dart';
+import 'package:omemo_dart/src/omemo/device.dart';
+
+abstract class OmemoEvent {}
+
+/// Triggered when a ratchet has been modified
+class RatchetModifiedEvent extends OmemoEvent {
+  RatchetModifiedEvent(
+    this.jid,
+    this.deviceId,
+    this.ratchet,
+    this.added,
+    this.replaced,
+  );
+  final String jid;
+  final int deviceId;
+  final OmemoDoubleRatchet ratchet;
+
+  /// Indicates whether the ratchet has just been created (true) or just modified (false).
+  final bool added;
+
+  /// Indicates whether the ratchet has been replaced (true) or not.
+  final bool replaced;
+}
+
+/// Triggered when a ratchet has been removed and should be removed from storage.
+class RatchetRemovedEvent extends OmemoEvent {
+  RatchetRemovedEvent(this.jid, this.deviceId);
+  final String jid;
+  final int deviceId;
+}
+
+/// Triggered when the device map has been modified
+class DeviceListModifiedEvent extends OmemoEvent {
+  DeviceListModifiedEvent(this.list);
+  final Map<String, List<int>> list;
+}
+
+/// Triggered by the OmemoSessionManager when our own device bundle was modified
+/// and thus should be republished.
+class DeviceModifiedEvent extends OmemoEvent {
+  DeviceModifiedEvent(this.device);
+  final OmemoDevice device;
+}

lib/src/omemo/omemomanager.dart

@@ -0,0 +1,854 @@
+import 'dart:async';
+import 'dart:collection';
+import 'dart:convert';
+import 'package:collection/collection.dart';
+import 'package:cryptography/cryptography.dart';
+import 'package:hex/hex.dart';
+import 'package:logging/logging.dart';
+import 'package:meta/meta.dart';
+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/keys.dart';
+import 'package:omemo_dart/src/omemo/bundle.dart';
+import 'package:omemo_dart/src/omemo/constants.dart';
+import 'package:omemo_dart/src/omemo/decryption_result.dart';
+import 'package:omemo_dart/src/omemo/device.dart';
+import 'package:omemo_dart/src/omemo/encrypted_key.dart';
+import 'package:omemo_dart/src/omemo/encryption_result.dart';
+import 'package:omemo_dart/src/omemo/events.dart';
+import 'package:omemo_dart/src/omemo/fingerprint.dart';
+import 'package:omemo_dart/src/omemo/ratchet_map_key.dart';
+import 'package:omemo_dart/src/omemo/stanza.dart';
+import 'package:omemo_dart/src/protobuf/omemo_authenticated_message.dart';
+import 'package:omemo_dart/src/protobuf/omemo_key_exchange.dart';
+import 'package:omemo_dart/src/protobuf/omemo_message.dart';
+import 'package:omemo_dart/src/trust/base.dart';
+import 'package:omemo_dart/src/x3dh/x3dh.dart';
+import 'package:synchronized/synchronized.dart';
+
+class _InternalDecryptionResult {
+  const _InternalDecryptionResult(
+    this.ratchetCreated,
+    this.ratchetReplaced,
+    this.payload,
+  ) : assert(
+          !ratchetCreated || !ratchetReplaced,
+          'Ratchet must be either replaced or created',
+        );
+  final bool ratchetCreated;
+  final bool ratchetReplaced;
+  final String? payload;
+}
+
+class OmemoManager {
+  OmemoManager(
+    this._device,
+    this._trustManager,
+    this.sendEmptyOmemoMessageImpl,
+    this.fetchDeviceListImpl,
+    this.fetchDeviceBundleImpl,
+    this.subscribeToDeviceListNodeImpl,
+  );
+
+  final Logger _log = Logger('OmemoManager');
+
+  /// Functions for connecting with the OMEMO library
+
+  /// Send an empty OMEMO:2 message using the encrypted payload @result to
+  /// @recipientJid.
+  final Future<void> Function(EncryptionResult result, String recipientJid)
+      sendEmptyOmemoMessageImpl;
+
+  /// Fetch the list of device ids associated with @jid. If the device list cannot be
+  /// fetched, return null.
+  final Future<List<int>?> Function(String jid) fetchDeviceListImpl;
+
+  /// Fetch the device bundle for the device with id @id of jid. If it cannot be fetched, return null.
+  final Future<OmemoBundle?> Function(String jid, int id) fetchDeviceBundleImpl;
+
+  /// Subscribe to the device list PEP node of @jid.
+  final Future<void> Function(String jid) subscribeToDeviceListNodeImpl;
+
+  /// Map bare JID to its known devices
+  Map<String, List<int>> _deviceList = {};
+
+  /// Map bare JIDs to whether we already requested the device list once
+  final Map<String, bool> _deviceListRequested = {};
+
+  /// Map bare a ratchet key to its ratchet. Note that this is also locked by
+  /// _ratchetCriticalSectionLock.
+  Map<RatchetMapKey, OmemoDoubleRatchet> _ratchetMap = {};
+
+  /// Map bare JID to whether we already tried to subscribe to the device list node.
+  final Map<String, bool> _subscriptionMap = {};
+
+  /// For preventing a race condition in encryption/decryption
+  final Map<String, Queue<Completer<void>>> _ratchetCriticalSectionQueue = {};
+  final Lock _ratchetCriticalSectionLock = Lock();
+
+  /// The OmemoManager's trust management
+  final TrustManager _trustManager;
+  TrustManager get trustManager => _trustManager;
+
+  /// Our own keys...
+  final Lock _deviceLock = Lock();
+  // ignore: prefer_final_fields
+  OmemoDevice _device;
+
+  /// The event bus of the session manager
+  final StreamController<OmemoEvent> _eventStreamController =
+      StreamController<OmemoEvent>.broadcast();
+  Stream<OmemoEvent> get eventStream => _eventStreamController.stream;
+
+  /// Enter the critical section for performing cryptographic operations on the ratchets
+  Future<void> _enterRatchetCriticalSection(String jid) async {
+    final completer = await _ratchetCriticalSectionLock.synchronized(() {
+      if (_ratchetCriticalSectionQueue.containsKey(jid)) {
+        final c = Completer<void>();
+        _ratchetCriticalSectionQueue[jid]!.addLast(c);
+        return c;
+      }
+
+      _ratchetCriticalSectionQueue[jid] = Queue();
+      return null;
+    });
+
+    if (completer != null) {
+      await completer.future;
+    }
+  }
+
+  /// Leave the critical section for the ratchets.
+  Future<void> _leaveRatchetCriticalSection(String jid) async {
+    await _ratchetCriticalSectionLock.synchronized(() {
+      if (_ratchetCriticalSectionQueue.containsKey(jid)) {
+        if (_ratchetCriticalSectionQueue[jid]!.isEmpty) {
+          _ratchetCriticalSectionQueue.remove(jid);
+        } else {
+          _ratchetCriticalSectionQueue[jid]!.removeFirst().complete();
+        }
+      }
+    });
+  }
+
+  Future<String?> _decryptAndVerifyHmac(
+    List<int>? ciphertext,
+    List<int> keyAndHmac,
+  ) async {
+    // Empty OMEMO messages should just have the key decrypted and/or session set up.
+    if (ciphertext == null) {
+      return null;
+    }
+
+    final key = keyAndHmac.sublist(0, 32);
+    final hmac = keyAndHmac.sublist(32, 48);
+    final derivedKeys = await deriveEncryptionKeys(key, omemoPayloadInfoString);
+    final computedHmac =
+        await truncatedHmac(ciphertext, derivedKeys.authenticationKey);
+    if (!listsEqual(hmac, computedHmac)) {
+      throw InvalidMessageHMACException();
+    }
+
+    return utf8.decode(
+      await aes256CbcDecrypt(
+        ciphertext,
+        derivedKeys.encryptionKey,
+        derivedKeys.iv,
+      ),
+    );
+  }
+
+  /// Add a session [ratchet] with the [deviceId] to the internal tracking state.
+  /// NOTE: Must be called from within the ratchet critical section.
+  void _addSession(String jid, int deviceId, OmemoDoubleRatchet ratchet) {
+    // Add the bundle Id
+    if (!_deviceList.containsKey(jid)) {
+      _deviceList[jid] = [deviceId];
+
+      // Commit the device map
+      _eventStreamController.add(DeviceListModifiedEvent(_deviceList));
+    } else {
+      // Prevent having the same device multiple times in the list
+      if (!_deviceList[jid]!.contains(deviceId)) {
+        _deviceList[jid]!.add(deviceId);
+
+        // Commit the device map
+        _eventStreamController.add(DeviceListModifiedEvent(_deviceList));
+      }
+    }
+
+    // Add the ratchet session
+    final key = RatchetMapKey(jid, deviceId);
+    _ratchetMap[key] = ratchet;
+
+    // Commit the ratchet
+    _eventStreamController
+        .add(RatchetModifiedEvent(jid, deviceId, ratchet, true, false));
+  }
+
+  /// Build a new session with the user at [jid] with the device [deviceId] using data
+  /// from the key exchange [kex]. In case [kex] contains an unknown Signed Prekey
+  /// identifier an UnknownSignedPrekeyException will be thrown.
+  Future<OmemoDoubleRatchet> _addSessionFromKeyExchange(
+    String jid,
+    int deviceId,
+    OmemoKeyExchange kex,
+  ) async {
+    // Pick the correct SPK
+    final device = await getDevice();
+    OmemoKeyPair spk;
+    if (kex.spkId == _device.spkId) {
+      spk = _device.spk;
+    } else if (kex.spkId == _device.oldSpkId) {
+      spk = _device.oldSpk!;
+    } else {
+      throw UnknownSignedPrekeyException();
+    }
+
+    final kexResult = await x3dhFromInitialMessage(
+      X3DHMessage(
+        OmemoPublicKey.fromBytes(kex.ik!, KeyPairType.ed25519),
+        OmemoPublicKey.fromBytes(kex.ek!, KeyPairType.x25519),
+        kex.pkId!,
+      ),
+      spk,
+      device.opks.values.elementAt(kex.pkId!),
+      device.ik,
+    );
+    final ratchet = await OmemoDoubleRatchet.acceptNewSession(
+      spk,
+      OmemoPublicKey.fromBytes(kex.ik!, KeyPairType.ed25519),
+      kexResult.sk,
+      kexResult.ad,
+      getTimestamp(),
+    );
+
+    // Notify the trust manager
+    await trustManager.onNewSession(jid, deviceId);
+
+    return ratchet;
+  }
+
+  /// Create a ratchet session initiated by Alice to the user with Jid [jid] and the device
+  /// [deviceId] from the bundle [bundle].
+  @visibleForTesting
+  Future<OmemoKeyExchange> addSessionFromBundle(
+    String jid,
+    int deviceId,
+    OmemoBundle bundle,
+  ) async {
+    final device = await getDevice();
+    final kexResult = await x3dhFromBundle(
+      bundle,
+      device.ik,
+    );
+    final ratchet = await OmemoDoubleRatchet.initiateNewSession(
+      bundle.spk,
+      bundle.ik,
+      kexResult.sk,
+      kexResult.ad,
+      getTimestamp(),
+    );
+
+    await _trustManager.onNewSession(jid, deviceId);
+    _addSession(jid, deviceId, ratchet);
+
+    return OmemoKeyExchange()
+      ..pkId = kexResult.opkId
+      ..spkId = bundle.spkId
+      ..ik = await device.ik.pk.getBytes()
+      ..ek = await kexResult.ek.pk.getBytes();
+  }
+
+  /// In case a decryption error occurs, the Double Ratchet spec says to just restore
+  /// the ratchet to its old state. As such, this function restores the ratchet at
+  /// [mapKey] with [oldRatchet].
+  /// NOTE: Must be called from within the ratchet critical section
+  void _restoreRatchet(RatchetMapKey mapKey, OmemoDoubleRatchet oldRatchet) {
+    _log.finest(
+      'Restoring ratchet ${mapKey.jid}:${mapKey.deviceId} to ${oldRatchet.nr}',
+    );
+    _ratchetMap[mapKey] = oldRatchet;
+
+    // Commit the ratchet
+    _eventStreamController.add(
+      RatchetModifiedEvent(
+        mapKey.jid,
+        mapKey.deviceId,
+        oldRatchet,
+        false,
+        false,
+      ),
+    );
+  }
+
+  /// Attempt to decrypt [ciphertext]. [keys] refers to the <key /> elements inside the
+  /// <keys /> element with a "jid" attribute matching our own. [senderJid] refers to the
+  /// bare Jid of the sender. [senderDeviceId] refers to the "sid" attribute of the
+  /// <encrypted /> element.
+  /// [timestamp] refers to the time the message was sent. This might be either what the
+  /// server tells you via "XEP-0203: Delayed Delivery" or the point in time at which
+  /// you received the stanza, if no Delayed Delivery element was found.
+  ///
+  /// If the received message is an empty OMEMO message, i.e. there is no <payload />
+  /// element, then [ciphertext] must be set to null. In this case, this function
+  /// will return null as there is no message to be decrypted. This, however, is used
+  /// to set up sessions or advance the ratchets.
+  Future<_InternalDecryptionResult> _decryptMessage(
+    List<int>? ciphertext,
+    String senderJid,
+    int senderDeviceId,
+    List<EncryptedKey> keys,
+    int timestamp,
+  ) async {
+    // Try to find a session we can decrypt with.
+    var device = await getDevice();
+    final rawKey = keys.firstWhereOrNull((key) => key.rid == device.id);
+    if (rawKey == null) {
+      throw NotEncryptedForDeviceException();
+    }
+
+    final decodedRawKey = base64.decode(rawKey.value);
+    List<int>? keyAndHmac;
+    OmemoAuthenticatedMessage authMessage;
+    OmemoMessage? message;
+
+    // If the ratchet already existed, we store it. If it didn't, oldRatchet will stay
+    // null.
+    final ratchetKey = RatchetMapKey(senderJid, senderDeviceId);
+    final oldRatchet = getRatchet(ratchetKey)?.clone();
+    if (rawKey.kex) {
+      final kex = OmemoKeyExchange.fromBuffer(decodedRawKey);
+      authMessage = kex.message!;
+      message = OmemoMessage.fromBuffer(authMessage.message!);
+
+      // Guard against old key exchanges
+      if (oldRatchet != null) {
+        _log.finest(
+          'KEX for existent ratchet ${ratchetKey.toJsonKey()}. ${oldRatchet.kexTimestamp} > $timestamp: ${oldRatchet.kexTimestamp > timestamp}',
+        );
+        if (oldRatchet.kexTimestamp > timestamp) {
+          throw InvalidKeyExchangeException();
+        }
+      }
+
+      final r =
+          await _addSessionFromKeyExchange(senderJid, senderDeviceId, kex);
+
+      // Try to decrypt with the new ratchet r
+      try {
+        keyAndHmac =
+            await r.ratchetDecrypt(message, authMessage.writeToBuffer());
+        final result = await _decryptAndVerifyHmac(ciphertext, keyAndHmac);
+
+        // Add the new ratchet
+        _addSession(senderJid, senderDeviceId, r);
+
+        // Replace the OPK
+        await _deviceLock.synchronized(() async {
+          device = await device.replaceOnetimePrekey(kex.pkId!);
+
+          // Commit the device
+          _eventStreamController.add(DeviceModifiedEvent(device));
+        });
+
+        // Commit the ratchet
+        _eventStreamController.add(
+          RatchetModifiedEvent(
+            senderJid,
+            senderDeviceId,
+            r,
+            oldRatchet == null,
+            oldRatchet != null,
+          ),
+        );
+
+        return _InternalDecryptionResult(
+          oldRatchet == null,
+          oldRatchet != null,
+          result,
+        );
+      } catch (ex) {
+        _log.finest('Kex failed due to $ex. Not proceeding with kex.');
+      }
+    } else {
+      authMessage = OmemoAuthenticatedMessage.fromBuffer(decodedRawKey);
+      message = OmemoMessage.fromBuffer(authMessage.message!);
+    }
+
+    final devices = _deviceList[senderJid];
+    if (devices?.contains(senderDeviceId) != true) {
+      throw NoDecryptionKeyException();
+    }
+
+    // TODO(PapaTutuWawa): When receiving a message that is not an OMEMOKeyExchange from a device there is no session with, clients SHOULD create a session with that device and notify it about the new session by responding with an empty OMEMO message as per Sending a message.
+
+    // We can guarantee that the ratchet exists at this point in time
+    final ratchet = getRatchet(ratchetKey)!;
+
+    try {
+      if (rawKey.kex) {
+        keyAndHmac =
+            await ratchet.ratchetDecrypt(message, authMessage.writeToBuffer());
+      } else {
+        keyAndHmac = await ratchet.ratchetDecrypt(message, decodedRawKey);
+      }
+    } catch (_) {
+      _restoreRatchet(ratchetKey, oldRatchet!);
+      rethrow;
+    }
+
+    // Commit the ratchet
+    _eventStreamController.add(
+      RatchetModifiedEvent(
+        senderJid,
+        senderDeviceId,
+        ratchet,
+        false,
+        false,
+      ),
+    );
+
+    try {
+      return _InternalDecryptionResult(
+        false,
+        false,
+        await _decryptAndVerifyHmac(ciphertext, keyAndHmac),
+      );
+    } catch (_) {
+      _restoreRatchet(ratchetKey, oldRatchet!);
+      rethrow;
+    }
+  }
+
+  /// Returns, if it exists, the ratchet associated with [key].
+  /// NOTE: Must be called from within the ratchet critical section.
+  @visibleForTesting
+  OmemoDoubleRatchet? getRatchet(RatchetMapKey key) => _ratchetMap[key];
+
+  /// Figure out what bundles we have to still build a session with.
+  Future<List<OmemoBundle>> _fetchNewBundles(String jid) async {
+    // Check if we already requested the device list for [jid]
+    List<int> bundlesToFetch;
+    if (!_deviceListRequested.containsKey(jid) ||
+        !_deviceList.containsKey(jid)) {
+      // We don't have an up-to-date version of the device list
+      final newDeviceList = await fetchDeviceListImpl(jid);
+      if (newDeviceList == null) return [];
+
+      _deviceList[jid] = newDeviceList;
+      bundlesToFetch = newDeviceList.where((id) {
+        return !_ratchetMap.containsKey(RatchetMapKey(jid, id)) ||
+            _deviceList[jid]?.contains(id) == false;
+      }).toList();
+
+      // Trigger an event with the new device list
+      _eventStreamController.add(DeviceListModifiedEvent(_deviceList));
+    } else {
+      // We already have an up-to-date version of the device list
+      bundlesToFetch = _deviceList[jid]!
+          .where((id) => !_ratchetMap.containsKey(RatchetMapKey(jid, id)))
+          .toList();
+    }
+
+    if (bundlesToFetch.isNotEmpty) {
+      _log.finest('Fetching bundles $bundlesToFetch for $jid');
+    }
+
+    final device = await getDevice();
+    final newBundles = List<OmemoBundle>.empty(growable: true);
+    for (final id in bundlesToFetch) {
+      if (jid == device.jid && id == device.id) continue;
+
+      final bundle = await fetchDeviceBundleImpl(jid, id);
+      if (bundle != null) newBundles.add(bundle);
+    }
+
+    return newBundles;
+  }
+
+  /// Encrypt the key [plaintext] for all known bundles of the Jids in [jids]. Returns a
+  /// map that maps the device Id to the ciphertext of [plaintext].
+  ///
+  /// If [plaintext] is null, then the result will be an empty OMEMO message, i.e. one that
+  /// does not contain a <payload /> element. This means that the ciphertext attribute of
+  /// the result will be null as well.
+  /// NOTE: Must be called within the ratchet critical section
+  Future<EncryptionResult> _encryptToJids(
+    List<String> jids,
+    String? plaintext,
+  ) async {
+    final encryptedKeys = List<EncryptedKey>.empty(growable: true);
+
+    var ciphertext = const <int>[];
+    var keyPayload = const <int>[];
+    if (plaintext != null) {
+      // Generate the key and encrypt the plaintext
+      final key = generateRandomBytes(32);
+      final keys = await deriveEncryptionKeys(key, omemoPayloadInfoString);
+      ciphertext = await aes256CbcEncrypt(
+        utf8.encode(plaintext),
+        keys.encryptionKey,
+        keys.iv,
+      );
+      final hmac = await truncatedHmac(ciphertext, keys.authenticationKey);
+      keyPayload = concat([key, hmac]);
+    } else {
+      keyPayload = List<int>.filled(32, 0x0);
+    }
+
+    final kex = <RatchetMapKey, OmemoKeyExchange>{};
+    for (final jid in jids) {
+      for (final newSession in await _fetchNewBundles(jid)) {
+        kex[RatchetMapKey(jid, newSession.id)] = await addSessionFromBundle(
+          newSession.jid,
+          newSession.id,
+          newSession,
+        );
+      }
+    }
+
+    // We assume that the user already checked if the session exists
+    final deviceEncryptionErrors = <RatchetMapKey, OmemoException>{};
+    final jidEncryptionErrors = <String, OmemoException>{};
+    for (final jid in jids) {
+      final devices = _deviceList[jid];
+      if (devices == null) {
+        _log.severe('Device list does not exist for $jid.');
+        jidEncryptionErrors[jid] = NoKeyMaterialAvailableException();
+        continue;
+      }
+
+      if (!_subscriptionMap.containsKey(jid)) {
+        unawaited(subscribeToDeviceListNodeImpl(jid));
+        _subscriptionMap[jid] = true;
+      }
+
+      for (final deviceId in devices) {
+        // Empty OMEMO messages are allowed to bypass trust
+        if (plaintext != null) {
+          // Only encrypt to devices that are trusted
+          if (!(await _trustManager.isTrusted(jid, deviceId))) continue;
+
+          // Only encrypt to devices that are enabled
+          if (!(await _trustManager.isEnabled(jid, deviceId))) continue;
+        }
+
+        final ratchetKey = RatchetMapKey(jid, deviceId);
+        var ratchet = _ratchetMap[ratchetKey];
+        if (ratchet == null) {
+          _log.severe('Ratchet ${ratchetKey.toJsonKey()} does not exist.');
+          deviceEncryptionErrors[ratchetKey] =
+              NoKeyMaterialAvailableException();
+          continue;
+        }
+
+        final ciphertext =
+            (await ratchet.ratchetEncrypt(keyPayload)).ciphertext;
+
+        if (kex.containsKey(ratchetKey)) {
+          // The ratchet did not exist
+          final k = kex[ratchetKey]!
+            ..message = OmemoAuthenticatedMessage.fromBuffer(ciphertext);
+          final buffer = base64.encode(k.writeToBuffer());
+          encryptedKeys.add(
+            EncryptedKey(
+              jid,
+              deviceId,
+              buffer,
+              true,
+            ),
+          );
+
+          ratchet = ratchet.cloneWithKex(buffer);
+          _ratchetMap[ratchetKey] = ratchet;
+        } else if (!ratchet.acknowledged) {
+          // The ratchet exists but is not acked
+          if (ratchet.kex != null) {
+            final oldKex =
+                OmemoKeyExchange.fromBuffer(base64.decode(ratchet.kex!))
+                  ..message = OmemoAuthenticatedMessage.fromBuffer(ciphertext);
+
+            encryptedKeys.add(
+              EncryptedKey(
+                jid,
+                deviceId,
+                base64.encode(oldKex.writeToBuffer()),
+                true,
+              ),
+            );
+          } else {
+            // The ratchet is not acked but we don't have the old key exchange
+            _log.warning(
+              'Ratchet for $jid:$deviceId is not acked but the kex attribute is null',
+            );
+            encryptedKeys.add(
+              EncryptedKey(
+                jid,
+                deviceId,
+                base64.encode(ciphertext),
+                false,
+              ),
+            );
+          }
+        } else {
+          // The ratchet exists and is acked
+          encryptedKeys.add(
+            EncryptedKey(
+              jid,
+              deviceId,
+              base64.encode(ciphertext),
+              false,
+            ),
+          );
+        }
+
+        // Commit the ratchet
+        _eventStreamController
+            .add(RatchetModifiedEvent(jid, deviceId, ratchet, false, false));
+      }
+    }
+
+    return EncryptionResult(
+      plaintext != null ? ciphertext : null,
+      encryptedKeys,
+      deviceEncryptionErrors,
+      jidEncryptionErrors,
+    );
+  }
+
+  /// Call when receiving an OMEMO:2 encrypted stanza. Will handle everything and
+  /// decrypt it.
+  Future<DecryptionResult> onIncomingStanza(OmemoIncomingStanza stanza) async {
+    await _enterRatchetCriticalSection(stanza.bareSenderJid);
+
+    if (!_subscriptionMap.containsKey(stanza.bareSenderJid)) {
+      unawaited(subscribeToDeviceListNodeImpl(stanza.bareSenderJid));
+      _subscriptionMap[stanza.bareSenderJid] = true;
+    }
+
+    final ratchetKey =
+        RatchetMapKey(stanza.bareSenderJid, stanza.senderDeviceId);
+    final _InternalDecryptionResult result;
+    try {
+      result = await _decryptMessage(
+        stanza.payload != null ? base64.decode(stanza.payload!) : null,
+        stanza.bareSenderJid,
+        stanza.senderDeviceId,
+        stanza.keys,
+        stanza.timestamp,
+      );
+    } on OmemoException catch (ex) {
+      await _leaveRatchetCriticalSection(stanza.bareSenderJid);
+      return DecryptionResult(
+        null,
+        ex,
+      );
+    }
+
+    // Check if the ratchet is acked
+    final ratchet = getRatchet(ratchetKey);
+    assert(
+      ratchet != null,
+      'We decrypted the message, so the ratchet must exist',
+    );
+
+    if (ratchet!.acknowledged) {
+      // Ratchet is acknowledged
+      if (ratchet.nr > 53 || result.ratchetCreated || result.ratchetReplaced) {
+        await sendEmptyOmemoMessageImpl(
+          await _encryptToJids(
+            [stanza.bareSenderJid],
+            null,
+          ),
+          stanza.bareSenderJid,
+        );
+      }
+
+      // Ratchet is acked
+      await _leaveRatchetCriticalSection(stanza.bareSenderJid);
+      return DecryptionResult(
+        result.payload,
+        null,
+      );
+    } else {
+      // Ratchet is not acked.
+      // Mark as acked and send an empty OMEMO message.
+      await ratchetAcknowledged(
+        stanza.bareSenderJid,
+        stanza.senderDeviceId,
+        enterCriticalSection: false,
+      );
+      await sendEmptyOmemoMessageImpl(
+        await _encryptToJids(
+          [stanza.bareSenderJid],
+          null,
+        ),
+        stanza.bareSenderJid,
+      );
+
+      await _leaveRatchetCriticalSection(stanza.bareSenderJid);
+      return DecryptionResult(
+        result.payload,
+        null,
+      );
+    }
+  }
+
+  /// Call when sending out an encrypted stanza. Will handle everything and
+  /// encrypt it.
+  Future<EncryptionResult> onOutgoingStanza(OmemoOutgoingStanza stanza) async {
+    _log.finest('Waiting to enter critical section');
+    await _enterRatchetCriticalSection(stanza.recipientJids.first);
+    _log.finest('Entered critical section');
+
+    final result = _encryptToJids(
+      stanza.recipientJids,
+      stanza.payload,
+    );
+
+    await _leaveRatchetCriticalSection(stanza.recipientJids.first);
+
+    return result;
+  }
+
+  // Sends a hearbeat message as specified by XEP-0384 to [jid].
+  Future<void> sendOmemoHeartbeat(String jid) async {
+    // TODO(Unknown): Include some error handling
+    final result = await _encryptToJids(
+      [jid],
+      null,
+    );
+    await sendEmptyOmemoMessageImpl(result, jid);
+  }
+
+  /// Mark the ratchet for device [deviceId] from [jid] as acked.
+  Future<void> ratchetAcknowledged(
+    String jid,
+    int deviceId, {
+    bool enterCriticalSection = true,
+  }) async {
+    if (enterCriticalSection) await _enterRatchetCriticalSection(jid);
+
+    final key = RatchetMapKey(jid, deviceId);
+    if (_ratchetMap.containsKey(key)) {
+      final ratchet = _ratchetMap[key]!..acknowledged = true;
+
+      // Commit it
+      _eventStreamController
+          .add(RatchetModifiedEvent(jid, deviceId, ratchet, false, false));
+    } else {
+      _log.severe(
+        'Attempted to acknowledge ratchet ${key.toJsonKey()}, even though it does not exist',
+      );
+    }
+
+    if (enterCriticalSection) await _leaveRatchetCriticalSection(jid);
+  }
+
+  /// Generates an entirely new device. May be useful when the user wants to reset their cryptographic
+  /// identity. Triggers an event to commit it to storage.
+  Future<void> regenerateDevice() async {
+    await _deviceLock.synchronized(() async {
+      _device = await OmemoDevice.generateNewDevice(_device.jid);
+
+      // Commit it
+      _eventStreamController.add(DeviceModifiedEvent(_device));
+    });
+  }
+
+  /// Returns the device used for encryption and decryption.
+  Future<OmemoDevice> getDevice() => _deviceLock.synchronized(() => _device);
+
+  /// Returns the id of the device used for encryption and decryption.
+  Future<int> getDeviceId() async => (await getDevice()).id;
+
+  /// Directly aquire the current device as a OMEMO device bundle.
+  Future<OmemoBundle> getDeviceBundle() async => (await getDevice()).toBundle();
+
+  /// Directly aquire the current device's fingerprint.
+  Future<String> getDeviceFingerprint() async =>
+      (await getDevice()).getFingerprint();
+
+  /// Returns the fingerprints for all devices of [jid] that we have a session with.
+  /// If there are not sessions with [jid], then returns null.
+  Future<List<DeviceFingerprint>?> getFingerprintsForJid(String jid) async {
+    if (!_deviceList.containsKey(jid)) return null;
+
+    await _enterRatchetCriticalSection(jid);
+
+    final fingerprintKeys = _deviceList[jid]!
+        .map((id) => RatchetMapKey(jid, id))
+        .where((key) => _ratchetMap.containsKey(key));
+
+    final fingerprints = List<DeviceFingerprint>.empty(growable: true);
+    for (final key in fingerprintKeys) {
+      final curveKey = await _ratchetMap[key]!.ik.toCurve25519();
+      fingerprints.add(
+        DeviceFingerprint(
+          key.deviceId,
+          HEX.encode(await curveKey.getBytes()),
+        ),
+      );
+    }
+
+    await _leaveRatchetCriticalSection(jid);
+    return fingerprints;
+  }
+
+  /// Ensures that the device list is fetched again on the next message sending.
+  void onNewConnection() {
+    _deviceListRequested.clear();
+    _subscriptionMap.clear();
+  }
+
+  /// Sets the device list for [jid] to [devices]. Triggers a DeviceListModifiedEvent.
+  void onDeviceListUpdate(String jid, List<int> devices) {
+    _deviceList[jid] = devices;
+    _deviceListRequested[jid] = true;
+
+    // Trigger an event
+    _eventStreamController.add(DeviceListModifiedEvent(_deviceList));
+  }
+
+  void initialize(
+    Map<RatchetMapKey, OmemoDoubleRatchet> ratchetMap,
+    Map<String, List<int>> deviceList,
+  ) {
+    _deviceList = deviceList;
+    _ratchetMap = ratchetMap;
+  }
+
+  /// Removes all ratchets for JID [jid]. This also removes all trust decisions for
+  /// [jid] from the trust manager. This function triggers a RatchetRemovedEvent for
+  /// every removed ratchet and a DeviceListModifiedEvent afterwards. Behaviour for
+  /// the trust manager is dependent on its implementation.
+  Future<void> removeAllRatchets(String jid) async {
+    await _enterRatchetCriticalSection(jid);
+
+    for (final deviceId in _deviceList[jid]!) {
+      // Remove the ratchet and commit it
+      _ratchetMap.remove(RatchetMapKey(jid, deviceId));
+      _eventStreamController.add(RatchetRemovedEvent(jid, deviceId));
+    }
+
+    // Remove the devices from the device list cache and commit it
+    _deviceList.remove(jid);
+    _deviceListRequested.remove(jid);
+    _eventStreamController.add(DeviceListModifiedEvent(_deviceList));
+
+    // Remove trust decisions
+    await _trustManager.removeTrustDecisionsForJid(jid);
+
+    await _leaveRatchetCriticalSection(jid);
+  }
+
+  /// Replaces the internal device with [newDevice]. Does not trigger an event.
+  Future<void> replaceDevice(OmemoDevice newDevice) async {
+    await _deviceLock.synchronized(() {
+      _device = newDevice;
+    });
+  }
+}

lib/src/omemo/queue.dart

@@ -1,100 +0,0 @@
-import 'dart:async';
-import 'dart:collection';
-
-import 'package:meta/meta.dart';
-import 'package:synchronized/synchronized.dart';
-
-extension UtilAllMethodsList<T> on List<T> {
-  void removeAll(List<T> values) {
-    for (final value in values) {
-      remove(value);
-    }
-  }
-
-  bool containsAll(List<T> values) {
-    for (final value in values) {
-      if (!contains(value)) {
-        return false;
-      }
-    }
-
-    return true;
-  }
-}
-
-class _RatchetAccessQueueEntry {
-  _RatchetAccessQueueEntry(
-    this.jids,
-    this.completer,
-  );
-
-  final List<String> jids;
-  final Completer<void> completer;
-}
-
-class RatchetAccessQueue {
-  final Queue<_RatchetAccessQueueEntry> _queue = Queue();
-
-  @visibleForTesting
-  final List<String> runningOperations = List<String>.empty(growable: true);
-
-  final Lock lock = Lock();
-
-  bool canBypass(List<String> jids) {
-    for (final jid in jids) {
-      if (runningOperations.contains(jid)) {
-        return false;
-      }
-    }
-
-    return true;
-  }
-
-  Future<void> enterCriticalSection(List<String> jids) async {
-    final completer = await lock.synchronized<Completer<void>?>(() {
-      if (canBypass(jids)) {
-        runningOperations.addAll(jids);
-        return null;
-      }
-
-      final completer = Completer<void>();
-      _queue.add(
-        _RatchetAccessQueueEntry(
-          jids,
-          completer,
-        ),
-      );
-
-      return completer;
-    });
-
-    await completer?.future;
-  }
-
-  Future<void> leaveCriticalSection(List<String> jids) async {
-    await lock.synchronized(() {
-      runningOperations.removeAll(jids);
-
-      while (_queue.isNotEmpty) {
-        if (canBypass(_queue.first.jids)) {
-          final head = _queue.removeFirst();
-          runningOperations.addAll(head.jids);
-          head.completer.complete();
-        } else {
-          break;
-        }
-      }
-    });
-  }
-
-  Future<T> synchronized<T>(
-    List<String> jids,
-    Future<T> Function() function,
-  ) async {
-    await enterCriticalSection(jids);
-    final result = await function();
-    await leaveCriticalSection(jids);
-
-    return result;
-  }
-}

lib/src/omemo/ratchet_data.dart

@@ -1,26 +0,0 @@
-import 'package:omemo_dart/src/double_ratchet/double_ratchet.dart';
-
-class OmemoRatchetData {
-  const OmemoRatchetData(
-    this.jid,
-    this.id,
-    this.ratchet,
-    this.added,
-    this.replaced,
-  );
-
-  /// The JID we have the ratchet with.
-  final String jid;
-
-  /// The device id we have the ratchet with.
-  final int id;
-
-  /// The actual double ratchet to commit.
-  final OmemoDoubleRatchet ratchet;
-
-  /// Indicates whether the ratchet has just been created (true) or just modified (false).
-  final bool added;
-
-  /// Indicates whether the ratchet has been replaced (true) or not.
-  final bool replaced;
-}

lib/src/omemo/stanza.dart

@@ -5,9 +5,9 @@ class OmemoIncomingStanza {
   const OmemoIncomingStanza(
     this.bareSenderJid,
     this.senderDeviceId,
+    this.timestamp,
     this.keys,
     this.payload,
-    this.isCatchup,
   );
 
   /// The bare JID of the sender of the stanza.
@@ -16,14 +16,14 @@ class OmemoIncomingStanza {
   /// The device ID of the sender.
   final int senderDeviceId;
 
-  /// The included encrypted keys for our own JID
+  /// The timestamp when the stanza was received.
+  final int timestamp;
+
+  /// The included encrypted keys
   final List<EncryptedKey> keys;
 
   /// The string payload included in the <encrypted /> element.
   final String? payload;
-
-  /// Flag indicating whether the message was received due to a catchup.
-  final bool isCatchup;
 }
 
 /// Describes a stanza that is to be sent out
@@ -37,5 +37,5 @@ class OmemoOutgoingStanza {
   final List<String> recipientJids;
 
   /// The serialised XML data that should be encrypted.
-  final String? payload;
+  final String payload;
 }

lib/src/protobuf/omemo_authenticated_message.dart

@@ -0,0 +1,38 @@
+import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/protobuf/protobuf.dart';
+
+class OmemoAuthenticatedMessage {
+  OmemoAuthenticatedMessage();
+
+  factory OmemoAuthenticatedMessage.fromBuffer(List<int> data) {
+    var i = 0;
+
+    // required bytes mac     = 1;
+    if (data[0] != fieldId(1, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final mac = data.sublist(2, i + 2 + data[1]);
+    i += data[1] + 2;
+
+    if (data[i] != fieldId(2, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final message = data.sublist(i + 2, i + 2 + data[i + 1]);
+
+    return OmemoAuthenticatedMessage()
+      ..mac = mac
+      ..message = message;
+  }
+
+  List<int>? mac;
+  List<int>? message;
+
+  List<int> writeToBuffer() {
+    return concat([
+      [fieldId(1, fieldTypeByteArray), mac!.length],
+      mac!,
+      [fieldId(2, fieldTypeByteArray), message!.length],
+      message!,
+    ]);
+  }
+}

lib/src/protobuf/omemo_key_exchange.dart

@@ -0,0 +1,71 @@
+import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/protobuf/omemo_authenticated_message.dart';
+import 'package:omemo_dart/src/protobuf/protobuf.dart';
+
+class OmemoKeyExchange {
+  OmemoKeyExchange();
+
+  factory OmemoKeyExchange.fromBuffer(List<int> data) {
+    var i = 0;
+
+    if (data[i] != fieldId(1, fieldTypeUint32)) {
+      throw Exception();
+    }
+    var decoded = decodeVarint(data, 1);
+    final pkId = decoded.n;
+    i += decoded.length + 1;
+
+    if (data[i] != fieldId(2, fieldTypeUint32)) {
+      throw Exception();
+    }
+    decoded = decodeVarint(data, i + 1);
+    final spkId = decoded.n;
+    i += decoded.length + 1;
+
+    if (data[i] != fieldId(3, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final ik = data.sublist(i + 2, i + 2 + data[i + 1]);
+    i += 2 + data[i + 1];
+
+    if (data[i] != fieldId(4, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final ek = data.sublist(i + 2, i + 2 + data[i + 1]);
+    i += 2 + data[i + 1];
+
+    if (data[i] != fieldId(5, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final message = OmemoAuthenticatedMessage.fromBuffer(data.sublist(i + 2));
+
+    return OmemoKeyExchange()
+      ..pkId = pkId
+      ..spkId = spkId
+      ..ik = ik
+      ..ek = ek
+      ..message = message;
+  }
+
+  int? pkId;
+  int? spkId;
+  List<int>? ik;
+  List<int>? ek;
+  OmemoAuthenticatedMessage? message;
+
+  List<int> writeToBuffer() {
+    final msg = message!.writeToBuffer();
+    return concat([
+      [fieldId(1, fieldTypeUint32)],
+      encodeVarint(pkId!),
+      [fieldId(2, fieldTypeUint32)],
+      encodeVarint(spkId!),
+      [fieldId(3, fieldTypeByteArray), ik!.length],
+      ik!,
+      [fieldId(4, fieldTypeByteArray), ek!.length],
+      ek!,
+      [fieldId(5, fieldTypeByteArray), msg.length],
+      msg,
+    ]);
+  }
+}

lib/src/protobuf/omemo_message.dart

@@ -0,0 +1,75 @@
+import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/protobuf/protobuf.dart';
+
+class OmemoMessage {
+  OmemoMessage();
+
+  factory OmemoMessage.fromBuffer(List<int> data) {
+    var i = 0;
+
+    // required uint32 n          = 1;
+    if (data[0] != fieldId(1, fieldTypeUint32)) {
+      throw Exception();
+    }
+    var decode = decodeVarint(data, 1);
+    final n = decode.n;
+    i += decode.length + 1;
+
+    // required uint32 pn         = 2;
+    if (data[i] != fieldId(2, fieldTypeUint32)) {
+      throw Exception();
+    }
+    decode = decodeVarint(data, i + 1);
+    final pn = decode.n;
+    i += decode.length + 1;
+
+    // required bytes  dh_pub     = 3;
+    if (data[i] != fieldId(3, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final dhPub = data.sublist(i + 2, i + 2 + data[i + 1]);
+    i += 2 + data[i + 1];
+
+    // optional bytes  ciphertext = 4;
+    List<int>? ciphertext;
+    if (i < data.length) {
+      if (data[i] != fieldId(4, fieldTypeByteArray)) {
+        throw Exception();
+      }
+
+      ciphertext = data.sublist(i + 2, i + 2 + data[i + 1]);
+    }
+
+    return OmemoMessage()
+      ..n = n
+      ..pn = pn
+      ..dhPub = dhPub
+      ..ciphertext = ciphertext;
+  }
+
+  int? n;
+  int? pn;
+  List<int>? dhPub;
+  List<int>? ciphertext;
+
+  List<int> writeToBuffer() {
+    final data = concat([
+      [fieldId(1, fieldTypeUint32)],
+      encodeVarint(n!),
+      [fieldId(2, fieldTypeUint32)],
+      encodeVarint(pn!),
+      [fieldId(3, fieldTypeByteArray), dhPub!.length],
+      dhPub!,
+    ]);
+
+    if (ciphertext != null) {
+      return concat([
+        data,
+        [fieldId(4, fieldTypeByteArray), ciphertext!.length],
+        ciphertext!,
+      ]);
+    }
+
+    return data;
+  }
+}

lib/src/protobuf/protobuf.dart

@@ -0,0 +1,64 @@
+/// Masks the 7 LSB
+const lsb7Mask = 0x7F;
+
+/// Constant for setting the MSB
+const msb = 1 << 7;
+
+/// Field types
+const fieldTypeUint32 = 0;
+const fieldTypeByteArray = 2;
+
+int fieldId(int number, int type) {
+  return (number << 3) | type;
+}
+
+class VarintDecode {
+  const VarintDecode(this.n, this.length);
+  final int n;
+  final int length;
+}
+
+/// Decode a Varint that begins at [input]'s index [offset].
+VarintDecode decodeVarint(List<int> input, int offset) {
+  // The return value
+  var n = 0;
+  // The byte offset counter
+  var i = 0;
+
+  // Iterate until the MSB of the byte is 0
+  while (true) {
+    // Mask only the 7 LSB and "move" them accordingly
+    n += (input[offset + i] & lsb7Mask) << (7 * i);
+
+    // Break if we reached the end
+    if (input[offset + i] & 1 << 7 == 0) {
+      break;
+    }
+    i++;
+  }
+
+  return VarintDecode(n, i + 1);
+}
+
+// Encodes the integer [i] into a Varint.
+List<int> encodeVarint(int i) {
+  assert(i >= 0, "Two's complement is not implemented");
+  final ret = List<int>.empty(growable: true);
+
+  // Thanks to https://github.com/hathibelagal-dev/LEB128 for the trick with toRadixString!
+  final numSevenBlocks = (i.toRadixString(2).length / 7).ceil();
+  for (var j = 0; j < numSevenBlocks; j++) {
+    // The 7 LSB of the byte we're creating
+    final x = (i & (lsb7Mask << j * 7)) >> j * 7;
+
+    if (j == numSevenBlocks - 1) {
+      // If we were to shift further, we only get zero, so we're at the end
+      ret.add(x);
+    } else {
+      // We still have at least one bit more to go, so set the MSB to 1
+      ret.add(x + msb);
+    }
+  }
+
+  return ret;
+}

lib/src/trust/always.dart

@@ -22,5 +22,5 @@ class AlwaysTrustingTrustManager extends TrustManager {
   Future<void> removeTrustDecisionsForJid(String jid) async {}
 
   @override
-  Future<void> loadTrustData(String jid) async {}
+  Future<Map<String, dynamic>> toJson() async => <String, dynamic>{};
 }

lib/src/trust/base.dart

@@ -1,5 +1,3 @@
-import 'package:meta/meta.dart';
-
 /// The base class for managing trust in OMEMO sessions.
 // ignore: one_member_abstracts
 abstract class TrustManager {
@@ -9,7 +7,6 @@ abstract class TrustManager {
 
   /// Called by the OmemoSessionManager when a new session has been built. Should set
   /// a default trust state to [jid]'s device with identifier [deviceId].
-  @internal
   Future<void> onNewSession(String jid, int deviceId);
 
   /// Return true if the device with id [deviceId] of Jid [jid] should be used for encryption.
@@ -20,14 +17,9 @@ abstract class TrustManager {
   /// if [enabled] is false.
   Future<void> setEnabled(String jid, int deviceId, bool enabled);
 
-  /// Removes all trust decisions for [jid].
-  @internal
-  Future<void> removeTrustDecisionsForJid(String jid);
+  /// Serialize the trust manager to JSON.
+  Future<Map<String, dynamic>> toJson();
 
-  // ignore: comment_references
-  /// Called from within the [OmemoManager].
-  /// Loads the trust data for the JID [jid] from persistent storage
-  /// into the internal cache, if applicable.
-  @internal
-  Future<void> loadTrustData(String jid);
+  /// Removes all trust decisions for [jid].
+  Future<void> removeTrustDecisionsForJid(String jid);
 }

lib/src/trust/btbv.dart

@@ -1,116 +1,71 @@
 import 'package:meta/meta.dart';
-import 'package:omemo_dart/src/helpers.dart';
 import 'package:omemo_dart/src/omemo/ratchet_map_key.dart';
 import 'package:omemo_dart/src/trust/base.dart';
-
-@immutable
-class BTBVTrustData {
-  const BTBVTrustData(
-    this.jid,
-    this.device,
-    this.state,
-    this.enabled,
-    this.trusted,
-  );
-
-  /// The JID in question.
-  final String jid;
-
-  /// The device (ratchet) in question.
-  final int device;
-
-  /// The trust state of the ratchet.
-  final BTBVTrustState state;
-
-  /// Flag indicating whether the ratchet is enabled (true) or not (false).
-  final bool enabled;
-
-  /// Flag indicating whether the ratchet is trusted. For loading and commiting a ratchet, this field
-  /// contains an arbitrary value.
-  /// When using [BlindTrustBeforeVerificationTrustManager.getDevicesTrust], this flag will be true if
-  /// the ratchet is trusted and false if not.
-  final bool trusted;
-}
-
-/// A callback for when a trust decision is to be commited to persistent storage.
-typedef BTBVTrustCommitCallback = Future<void> Function(BTBVTrustData data);
-
-/// A stub-implementation of [BTBVTrustCommitCallback].
-Future<void> btbvCommitStub(BTBVTrustData _) async {}
-
-/// A callback for when all trust decisions for a JID should be removed from persistent storage.
-typedef BTBVRemoveTrustForJidCallback = Future<void> Function(String jid);
-
-/// A stub-implementation of [BTBVRemoveTrustForJidCallback].
-Future<void> btbvRemoveTrustStub(String _) async {}
-
-/// A callback for when trust data should be loaded.
-typedef BTBVLoadDataCallback = Future<List<BTBVTrustData>> Function(String jid);
-
-/// A stub-implementation for [BTBVLoadDataCallback].
-Future<List<BTBVTrustData>> btbvLoadDataStub(String _) async => [];
+import 'package:synchronized/synchronized.dart';
 
 /// Every device is in either of those two trust states:
 /// - notTrusted: The device is absolutely not trusted
 /// - blindTrust: The fingerprint is not verified using OOB means
 /// - verified: The fingerprint has been verified using OOB means
 enum BTBVTrustState {
-  notTrusted(1),
-  blindTrust(2),
-  verified(3);
+  notTrusted, // = 1
+  blindTrust, // = 2
+  verified, // = 3
+}
 
-  const BTBVTrustState(this.value);
-
-  factory BTBVTrustState.fromInt(int value) {
-    switch (value) {
-      case 1:
-        return BTBVTrustState.notTrusted;
-      case 2:
-        return BTBVTrustState.blindTrust;
-      case 3:
-        return BTBVTrustState.verified;
-      // TODO(Unknown): Should we handle this better?
-      default:
-        return BTBVTrustState.notTrusted;
-    }
+int _trustToInt(BTBVTrustState state) {
+  switch (state) {
+    case BTBVTrustState.notTrusted:
+      return 1;
+    case BTBVTrustState.blindTrust:
+      return 2;
+    case BTBVTrustState.verified:
+      return 3;
   }
+}
 
-  /// The value backing the trust state.
-  final int value;
+BTBVTrustState _trustFromInt(int i) {
+  switch (i) {
+    case 1:
+      return BTBVTrustState.notTrusted;
+    case 2:
+      return BTBVTrustState.blindTrust;
+    case 3:
+      return BTBVTrustState.verified;
+    default:
+      return BTBVTrustState.notTrusted;
+  }
 }
 
 /// A TrustManager that implements the idea of Blind Trust Before Verification.
 /// See https://gultsch.de/trust.html for more details.
-class BlindTrustBeforeVerificationTrustManager extends TrustManager {
+abstract class BlindTrustBeforeVerificationTrustManager extends TrustManager {
   BlindTrustBeforeVerificationTrustManager({
-    this.loadData = btbvLoadDataStub,
-    this.commit = btbvCommitStub,
-    this.removeTrust = btbvRemoveTrustStub,
-  });
+    Map<RatchetMapKey, BTBVTrustState>? trustCache,
+    Map<RatchetMapKey, bool>? enablementCache,
+    Map<String, List<int>>? devices,
+  })  : trustCache = trustCache ?? {},
+        enablementCache = enablementCache ?? {},
+        devices = devices ?? {},
+        _lock = Lock();
 
   /// The cache for mapping a RatchetMapKey to its trust state
   @visibleForTesting
   @protected
-  final Map<RatchetMapKey, BTBVTrustState> trustCache = {};
+  final Map<RatchetMapKey, BTBVTrustState> trustCache;
 
   /// The cache for mapping a RatchetMapKey to whether it is enabled or not
   @visibleForTesting
   @protected
-  final Map<RatchetMapKey, bool> enablementCache = {};
+  final Map<RatchetMapKey, bool> enablementCache;
 
   /// Mapping of Jids to their device identifiers
   @visibleForTesting
   @protected
-  final Map<String, List<int>> devices = {};
+  final Map<String, List<int>> devices;
 
-  /// Callback for loading trust data.
-  final BTBVLoadDataCallback loadData;
-
-  /// Callback for commiting trust data to persistent storage.
-  final BTBVTrustCommitCallback commit;
-
-  /// Callback for removing trust data for a JID.
-  final BTBVRemoveTrustForJidCallback removeTrust;
+  /// The lock for devices and trustCache
+  final Lock _lock;
 
   /// Returns true if [jid] has at least one device that is verified. If not, returns false.
   /// Note that this function accesses devices and trustCache, which requires that the
@@ -125,72 +80,69 @@ class BlindTrustBeforeVerificationTrustManager extends TrustManager {
 
   @override
   Future<bool> isTrusted(String jid, int deviceId) async {
-    final trustCacheValue = trustCache[RatchetMapKey(jid, deviceId)];
-    if (trustCacheValue == BTBVTrustState.notTrusted) {
-      return false;
-    } else if (trustCacheValue == BTBVTrustState.verified) {
-      // The key is verified, so it's safe.
-      return true;
-    } else {
-      if (_hasAtLeastOneVerifiedDevice(jid)) {
-        // Do not trust if there is at least one device with full trust
-        return false;
+    var returnValue = false;
+    await _lock.synchronized(() async {
+      final trustCacheValue = trustCache[RatchetMapKey(jid, deviceId)];
+      if (trustCacheValue == BTBVTrustState.notTrusted) {
+        returnValue = false;
+        return;
+      } else if (trustCacheValue == BTBVTrustState.verified) {
+        // The key is verified, so it's safe.
+        returnValue = true;
+        return;
       } else {
-        // We have not verified a key from [jid], so it is blind trust all the way.
-        return true;
+        if (_hasAtLeastOneVerifiedDevice(jid)) {
+          // Do not trust if there is at least one device with full trust
+          returnValue = false;
+          return;
+        } else {
+          // We have not verified a key from [jid], so it is blind trust all the way.
+          returnValue = true;
+          return;
+        }
       }
-    }
+    });
+
+    return returnValue;
   }
 
   @override
   Future<void> onNewSession(String jid, int deviceId) async {
-    final key = RatchetMapKey(jid, deviceId);
-    if (_hasAtLeastOneVerifiedDevice(jid)) {
-      trustCache[key] = BTBVTrustState.notTrusted;
-      enablementCache[key] = false;
-    } else {
-      trustCache[key] = BTBVTrustState.blindTrust;
-      enablementCache[key] = true;
-    }
+    await _lock.synchronized(() async {
+      final key = RatchetMapKey(jid, deviceId);
+      if (_hasAtLeastOneVerifiedDevice(jid)) {
+        trustCache[key] = BTBVTrustState.notTrusted;
+        enablementCache[key] = false;
+      } else {
+        trustCache[key] = BTBVTrustState.blindTrust;
+        enablementCache[key] = true;
+      }
 
-    // Append to the device list
-    devices.appendOrCreate(jid, deviceId, checkExistence: true);
+      if (devices.containsKey(jid)) {
+        devices[jid]!.add(deviceId);
+      } else {
+        devices[jid] = List<int>.from([deviceId]);
+      }
 
-    // Commit the state
-    await commit(
-      BTBVTrustData(
-        jid,
-        deviceId,
-        trustCache[key]!,
-        enablementCache[key]!,
-        false,
-      ),
-    );
+      // Commit the state
+      await commitState();
+    });
   }
 
   /// Returns a mapping from the device identifiers of [jid] to their trust state. If
   /// there are no devices known for [jid], then an empty map is returned.
-  Future<Map<int, BTBVTrustData>> getDevicesTrust(String jid) async {
-    final map = <int, BTBVTrustData>{};
+  Future<Map<int, BTBVTrustState>> getDevicesTrust(String jid) async {
+    return _lock.synchronized(() async {
+      final map = <int, BTBVTrustState>{};
 
-    if (!devices.containsKey(jid)) return map;
+      if (!devices.containsKey(jid)) return map;
 
-    for (final deviceId in devices[jid]!) {
-      final key = RatchetMapKey(jid, deviceId);
-      if (!trustCache.containsKey(key) || !enablementCache.containsKey(key)) {
-        continue;
+      for (final deviceId in devices[jid]!) {
+        map[deviceId] = trustCache[RatchetMapKey(jid, deviceId)]!;
       }
 
-      map[deviceId] = BTBVTrustData(
-        jid,
-        deviceId,
-        trustCache[key]!,
-        enablementCache[key]!,
-        await isTrusted(jid, deviceId),
-      );
-    }
-
-    return map;
+      return map;
+    });
   }
 
   /// Sets the trust of [jid]'s device with identifier [deviceId] to [state].
@@ -199,71 +151,108 @@ class BlindTrustBeforeVerificationTrustManager extends TrustManager {
     int deviceId,
     BTBVTrustState state,
   ) async {
-    final key = RatchetMapKey(jid, deviceId);
-    trustCache[key] = state;
+    await _lock.synchronized(() async {
+      trustCache[RatchetMapKey(jid, deviceId)] = state;
 
-    // Commit the state
-    await commit(
-      BTBVTrustData(
-        jid,
-        deviceId,
-        state,
-        enablementCache[key]!,
-        false,
-      ),
-    );
+      // Commit the state
+      await commitState();
+    });
   }
 
   @override
   Future<bool> isEnabled(String jid, int deviceId) async {
-    final value = enablementCache[RatchetMapKey(jid, deviceId)];
+    return _lock.synchronized(() async {
+      final value = enablementCache[RatchetMapKey(jid, deviceId)];
 
-    if (value == null) return false;
-    return value;
+      if (value == null) return false;
+      return value;
+    });
   }
 
   @override
   Future<void> setEnabled(String jid, int deviceId, bool enabled) async {
-    final key = RatchetMapKey(jid, deviceId);
-    enablementCache[key] = enabled;
+    await _lock.synchronized(() async {
+      enablementCache[RatchetMapKey(jid, deviceId)] = enabled;
+    });
 
     // Commit the state
-    await commit(
-      BTBVTrustData(
-        jid,
-        deviceId,
-        trustCache[key]!,
-        enabled,
-        false,
+    await commitState();
+  }
+
+  @override
+  Future<Map<String, dynamic>> toJson() async {
+    return {
+      'devices': devices,
+      'trust': trustCache.map(
+        (key, value) => MapEntry(
+          key.toJsonKey(),
+          _trustToInt(value),
+        ),
+      ),
+      'enable':
+          enablementCache.map((key, value) => MapEntry(key.toJsonKey(), value)),
+    };
+  }
+
+  /// From a serialized version of a BTBV trust manager, extract the device list.
+  /// NOTE: This is needed as Dart cannot just cast a List<dynamic> to List<int> and so on.
+  static Map<String, List<int>> deviceListFromJson(Map<String, dynamic> json) {
+    return (json['devices']! as Map<String, dynamic>).map<String, List<int>>(
+      (key, value) => MapEntry(
+        key,
+        (value as List<dynamic>).map<int>((i) => i as int).toList(),
+      ),
+    );
+  }
+
+  /// From a serialized version of a BTBV trust manager, extract the trust cache.
+  /// NOTE: This is needed as Dart cannot just cast a List<dynamic> to List<int> and so on.
+  static Map<RatchetMapKey, BTBVTrustState> trustCacheFromJson(
+    Map<String, dynamic> json,
+  ) {
+    return (json['trust']! as Map<String, dynamic>)
+        .map<RatchetMapKey, BTBVTrustState>(
+      (key, value) => MapEntry(
+        RatchetMapKey.fromJsonKey(key),
+        _trustFromInt(value as int),
+      ),
+    );
+  }
+
+  /// From a serialized version of a BTBV trust manager, extract the enable cache.
+  /// NOTE: This is needed as Dart cannot just cast a List<dynamic> to List<int> and so on.
+  static Map<RatchetMapKey, bool> enableCacheFromJson(
+    Map<String, dynamic> json,
+  ) {
+    return (json['enable']! as Map<String, dynamic>).map<RatchetMapKey, bool>(
+      (key, value) => MapEntry(
+        RatchetMapKey.fromJsonKey(key),
+        value as bool,
       ),
     );
   }
 
   @override
   Future<void> removeTrustDecisionsForJid(String jid) async {
-    // Clear the caches
-    for (final device in devices[jid]!) {
-      final key = RatchetMapKey(jid, device);
-      trustCache.remove(key);
-      enablementCache.remove(key);
-    }
-    devices.remove(jid);
-
-    // Commit the state
-    await removeTrust(jid);
+    await _lock.synchronized(() async {
+      devices.remove(jid);
+      await commitState();
+    });
   }
 
-  @override
-  Future<void> loadTrustData(String jid) async {
-    for (final result in await loadData(jid)) {
-      final key = RatchetMapKey(jid, result.device);
-      trustCache[key] = result.state;
-      enablementCache[key] = result.enabled;
-      devices.appendOrCreate(jid, result.device, checkExistence: true);
-    }
-  }
+  /// Called when the state of the trust manager has been changed. Allows the user to
+  /// commit the trust state to persistent storage.
+  @visibleForOverriding
+  Future<void> commitState();
 
   @visibleForTesting
   BTBVTrustState getDeviceTrust(String jid, int deviceId) =>
       trustCache[RatchetMapKey(jid, deviceId)]!;
 }
+
+/// A BTBV TrustManager that does not commit its state to persistent storage. Well suited
+/// for testing.
+class MemoryBTBVTrustManager extends BlindTrustBeforeVerificationTrustManager {
+  @override
+  Future<void> commitState() async {}
+}

lib/src/trust/never.dart

@@ -22,5 +22,5 @@ class NeverTrustingTrustManager extends TrustManager {
   Future<void> removeTrustDecisionsForJid(String jid) async {}
 
   @override
-  Future<void> loadTrustData(String jid) async {}
+  Future<Map<String, dynamic>> toJson() async => <String, dynamic>{};
 }

lib/src/x3dh/x3dh.dart

@@ -1,14 +1,15 @@
 import 'dart:convert';
 import 'dart:math';
 import 'package:cryptography/cryptography.dart';
-import 'package:moxlib/moxlib.dart';
-import 'package:omemo_dart/src/common/constants.dart';
 import 'package:omemo_dart/src/crypto.dart';
 import 'package:omemo_dart/src/errors.dart';
 import 'package:omemo_dart/src/helpers.dart';
 import 'package:omemo_dart/src/keys.dart';
 import 'package:omemo_dart/src/omemo/bundle.dart';
 
+/// The overarching assumption is that we use Ed25519 keys for the identity keys
+const omemoX3DHInfoString = 'OMEMO X3DH';
+
 /// Performed by Alice
 class X3DHAliceResult {
   const X3DHAliceResult(this.ek, this.sk, this.opkId, this.ad);
@@ -69,8 +70,7 @@ Future<List<int>> kdf(List<int> km) async {
 
 /// Alice builds a session with Bob using his bundle [bundle] and Alice's identity key
 /// pair [ik].
-Future<Result<InvalidKeyExchangeSignatureError, X3DHAliceResult>>
-    x3dhFromBundle(
+Future<X3DHAliceResult> x3dhFromBundle(
   OmemoBundle bundle,
   OmemoKeyPair ik,
 ) async {
@@ -84,7 +84,7 @@ Future<Result<InvalidKeyExchangeSignatureError, X3DHAliceResult>>
   );
 
   if (!signatureValue) {
-    return Result(InvalidKeyExchangeSignatureError());
+    throw InvalidSignatureException();
   }
 
   // Generate EK
@@ -106,7 +106,7 @@ Future<Result<InvalidKeyExchangeSignatureError, X3DHAliceResult>>
     await bundle.ik.getBytes(),
   ]);
 
-  return Result(X3DHAliceResult(ek, sk, opkId, ad));
+  return X3DHAliceResult(ek, sk, opkId, ad);
 }
 
 /// Bob builds the X3DH shared secret from the inital message [msg], the SPK [spk], the

pubspec.yaml

@@ -1,6 +1,6 @@
 name: omemo_dart
 description: An XMPP library independent OMEMO library
-version: 0.5.0
+version: 0.4.3
 homepage: https://github.com/PapaTutuWawa/omemo_dart
 publish_to: https://git.polynom.me/api/packages/PapaTutuWawa/pub
 
@@ -13,15 +13,12 @@ dependencies:
   hex: ^0.2.0
   logging: ^1.0.2
   meta: ^1.7.0
-  moxlib:
-    version: ^0.2.0
-    hosted: https://git.polynom.me/api/packages/Moxxy/pub
   pinenacl: ^0.5.1
-  protobuf: ^2.1.0
-  protoc_plugin: ^20.0.1
   synchronized: ^3.0.0+2
 
 dev_dependencies:
   lints: ^2.0.0
+  protobuf: ^2.1.0
+  protoc_plugin: ^20.0.1
   test: ^1.21.0
   very_good_analysis: ^3.0.1

test/double_ratchet_test.dart

@@ -1,10 +1,39 @@
+// ignore_for_file: avoid_print
 import 'dart:convert';
-import 'dart:developer';
 import 'package:cryptography/cryptography.dart';
 import 'package:omemo_dart/omemo_dart.dart';
+import 'package:omemo_dart/protobuf/schema.pb.dart';
+import 'package:omemo_dart/src/double_ratchet/crypto.dart';
 import 'package:test/test.dart';
 
 void main() {
+  test('Test encrypting and decrypting', () async {
+    final sessionAd = List<int>.filled(32, 0x0);
+    final mk = List<int>.filled(32, 0x1);
+    final plaintext = utf8.encode('Hallo');
+    final header = OMEMOMessage()
+      ..n = 0
+      ..pn = 0
+      ..dhPub = List<int>.empty();
+    final asd = concat([sessionAd, header.writeToBuffer()]);
+
+    final ciphertext = await encrypt(
+      mk,
+      plaintext,
+      asd,
+      sessionAd,
+    );
+
+    final decrypted = await decrypt(
+      mk,
+      ciphertext,
+      asd,
+      sessionAd,
+    );
+
+    expect(decrypted, plaintext);
+  });
+
   test('Test the Double Ratchet', () async {
     // Generate keys
     const bobJid = 'bob@other.example.server';
@@ -28,8 +57,7 @@ void main() {
     );
 
     // Alice does X3DH
-    final resultAliceRaw = await x3dhFromBundle(bundleBob, ikAlice);
-    final resultAlice = resultAliceRaw.get<X3DHAliceResult>();
+    final resultAlice = await x3dhFromBundle(bundleBob, ikAlice);
 
     // Alice sends the inital message to Bob
     // ...
@@ -46,28 +74,23 @@ void main() {
       ikBob,
     );
 
-    log('X3DH key exchange done');
+    print('X3DH key exchange done');
 
     // Alice and Bob now share sk as a common secret and ad
     // Build a session
     final alicesRatchet = await OmemoDoubleRatchet.initiateNewSession(
       spkBob.pk,
-      bundleBob.spkId,
       ikBob.pk,
-      ikAlice.pk,
-      resultAlice.ek.pk,
       resultAlice.sk,
       resultAlice.ad,
-      resultAlice.opkId,
+      0,
     );
     final bobsRatchet = await OmemoDoubleRatchet.acceptNewSession(
       spkBob,
-      bundleBob.spkId,
       ikAlice.pk,
-      2,
-      resultAlice.ek.pk,
       resultBob.sk,
       resultBob.ad,
+      0,
     );
 
     expect(alicesRatchet.sessionAd, bobsRatchet.sessionAd);
@@ -75,42 +98,40 @@ void main() {
     for (var i = 0; i < 100; i++) {
       final messageText = 'Hello, dear $i';
 
-      log('${i + 1}/100');
       if (i.isEven) {
         // Alice encrypts a message
         final aliceRatchetResult =
             await alicesRatchet.ratchetEncrypt(utf8.encode(messageText));
-        log('Alice sent the message');
+        print('Alice sent the message');
 
         // Alice sends it to Bob
         // ...
 
         // Bob tries to decrypt it
         final bobRatchetResult = await bobsRatchet.ratchetDecrypt(
-          aliceRatchetResult,
+          aliceRatchetResult.header,
+          aliceRatchetResult.ciphertext,
         );
-        log('Bob decrypted the message');
+        print('Bob decrypted the message');
 
-        expect(bobRatchetResult.isType<List<int>>(), true);
-        expect(bobRatchetResult.get<List<int>>(), utf8.encode(messageText));
+        expect(utf8.encode(messageText), bobRatchetResult);
       } else {
         // Bob sends a message to Alice
         final bobRatchetResult =
             await bobsRatchet.ratchetEncrypt(utf8.encode(messageText));
-        log('Bob sent the message');
+        print('Bob sent the message');
 
         // Bobs sends it to Alice
         // ...
 
         // Alice tries to decrypt it
         final aliceRatchetResult = await alicesRatchet.ratchetDecrypt(
-          bobRatchetResult,
+          bobRatchetResult.header,
+          bobRatchetResult.ciphertext,
         );
-        log('Alice decrypted the message');
+        print('Alice decrypted the message');
 
-        expect(aliceRatchetResult.isType<List<int>>(), true);
-        expect(aliceRatchetResult.get<List<int>>(), utf8.encode(messageText));
-        expect(utf8.encode(messageText), aliceRatchetResult.get<List<int>>());
+        expect(utf8.encode(messageText), aliceRatchetResult);
       }
     }
   });

test/protobuf_test.dart

@@ -0,0 +1,186 @@
+import 'package:omemo_dart/protobuf/schema.pb.dart';
+import 'package:omemo_dart/src/protobuf/omemo_authenticated_message.dart';
+import 'package:omemo_dart/src/protobuf/omemo_key_exchange.dart';
+import 'package:omemo_dart/src/protobuf/omemo_message.dart';
+import 'package:omemo_dart/src/protobuf/protobuf.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Base 128 Varints', () {
+    test('Test simple parsing of Varints', () {
+      expect(
+        decodeVarint(<int>[1], 0).n,
+        1,
+      );
+      expect(
+        decodeVarint(<int>[1], 0).length,
+        1,
+      );
+      expect(
+        decodeVarint(<int>[0x96, 0x01, 0x00], 0).n,
+        150,
+      );
+      expect(
+        decodeVarint(<int>[0x96, 0x01, 0x00], 0).length,
+        2,
+      );
+      expect(
+        decodeVarint(<int>[172, 2, 0x8], 0).n,
+        300,
+      );
+      expect(
+        decodeVarint(<int>[172, 2, 0x8], 0).length,
+        2,
+      );
+    });
+
+    test('Test encoding Varints', () {
+      expect(
+        encodeVarint(1),
+        <int>[1],
+      );
+      expect(
+        encodeVarint(150),
+        <int>[0x96, 0x01],
+      );
+      expect(
+        encodeVarint(300),
+        <int>[172, 2],
+      );
+    });
+
+    test('Test some special cases', () {
+      expect(decodeVarint(encodeVarint(1042464893), 0).n, 1042464893);
+    });
+  });
+
+  group('OMEMOMessage', () {
+    test('Decode a OMEMOMessage', () {
+      final pbMessage = OMEMOMessage()
+        ..n = 1
+        ..pn = 5
+        ..dhPub = <int>[1, 2, 3]
+        ..ciphertext = <int>[4, 5, 6];
+      final serial = pbMessage.writeToBuffer();
+      final msg = OmemoMessage.fromBuffer(serial);
+
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, <int>[4, 5, 6]);
+    });
+    test('Decode a OMEMOMessage without ciphertext', () {
+      final pbMessage = OMEMOMessage()
+        ..n = 1
+        ..pn = 5
+        ..dhPub = <int>[1, 2, 3];
+      final serial = pbMessage.writeToBuffer();
+      final msg = OmemoMessage.fromBuffer(serial);
+
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, null);
+    });
+    test('Encode a OMEMOMessage', () {
+      final m = OmemoMessage()
+        ..n = 1
+        ..pn = 5
+        ..dhPub = <int>[1, 2, 3]
+        ..ciphertext = <int>[4, 5, 6];
+      final serial = m.writeToBuffer();
+      final msg = OMEMOMessage.fromBuffer(serial);
+
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, <int>[4, 5, 6]);
+    });
+    test('Encode a OMEMOMessage without ciphertext', () {
+      final m = OmemoMessage()
+        ..n = 1
+        ..pn = 5
+        ..dhPub = <int>[1, 2, 3];
+      final serial = m.writeToBuffer();
+      final msg = OMEMOMessage.fromBuffer(serial);
+
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, <int>[]);
+    });
+  });
+
+  group('OMEMOAuthenticatedMessage', () {
+    test('Test encoding a message', () {
+      final msg = OmemoAuthenticatedMessage()
+        ..mac = <int>[1, 2, 3]
+        ..message = <int>[4, 5, 6];
+      final decoded = OMEMOAuthenticatedMessage.fromBuffer(msg.writeToBuffer());
+
+      expect(decoded.mac, <int>[1, 2, 3]);
+      expect(decoded.message, <int>[4, 5, 6]);
+    });
+    test('Test decoding a message', () {
+      final msg = OMEMOAuthenticatedMessage()
+        ..mac = <int>[1, 2, 3]
+        ..message = <int>[4, 5, 6];
+      final bytes = msg.writeToBuffer();
+      final decoded = OmemoAuthenticatedMessage.fromBuffer(bytes);
+
+      expect(decoded.mac, <int>[1, 2, 3]);
+      expect(decoded.message, <int>[4, 5, 6]);
+    });
+  });
+
+  group('OMEMOKeyExchange', () {
+    test('Test encoding a message', () {
+      final authMessage = OmemoAuthenticatedMessage()
+        ..mac = <int>[5, 6, 8, 0]
+        ..message = <int>[4, 5, 7, 3, 2];
+      final message = OmemoKeyExchange()
+        ..pkId = 698
+        ..spkId = 245
+        ..ik = <int>[1, 4, 6]
+        ..ek = <int>[4, 6, 7, 80]
+        ..message = authMessage;
+      final kex = OMEMOKeyExchange.fromBuffer(message.writeToBuffer());
+
+      expect(kex.pkId, 698);
+      expect(kex.spkId, 245);
+      expect(kex.ik, <int>[1, 4, 6]);
+      expect(kex.ek, <int>[4, 6, 7, 80]);
+
+      expect(kex.message.mac, <int>[5, 6, 8, 0]);
+      expect(kex.message.message, <int>[4, 5, 7, 3, 2]);
+    });
+    test('Test decoding a message', () {
+      final message = OMEMOAuthenticatedMessage()
+        ..mac = <int>[5, 6, 8, 0]
+        ..message = <int>[4, 5, 7, 3, 2];
+      final kex = OMEMOKeyExchange()
+        ..pkId = 698
+        ..spkId = 245
+        ..ik = <int>[1, 4, 6]
+        ..ek = <int>[4, 6, 7, 80]
+        ..message = message;
+      final decoded = OmemoKeyExchange.fromBuffer(kex.writeToBuffer());
+
+      expect(decoded.pkId, 698);
+      expect(decoded.spkId, 245);
+      expect(decoded.ik, <int>[1, 4, 6]);
+      expect(decoded.ek, <int>[4, 6, 7, 80]);
+
+      expect(decoded.message!.mac, <int>[5, 6, 8, 0]);
+      expect(decoded.message!.message, <int>[4, 5, 7, 3, 2]);
+    });
+    test('Test decoding an issue', () {
+      /*
+      final data = 'CAAQfRogc2GwslU219dUkrMHNM4KdZRmuFnBTae+bQaJ+55IsAMiII7aZKj2sUpb6xR/3Ari7WZUmKFV0G6czUc4NMvjKDBaKnwKEM2ZpI8X3TgcxhxwENANnlsSaAgAEAAaICy8T9WPgLb7RdYd8/4JkrLF0RahEkC3ZaEfk5jw3dsLIkBMILzLyByweLgF4lCn0oNea+kbdrFr6rY7r/7WyI8hXEQz38QpnN+jyGGwC7Ga0dq70WuyqE7VpiFArQwqZh2G';
+      final kex = OmemoKeyExchange.fromBuffer(base64Decode(data));
+
+      expect(kex.spkId!, 1042464893);
+      */
+    });
+  });
+}

test/queue_test.dart

@@ -1,62 +0,0 @@
-import 'dart:async';
-import 'package:omemo_dart/src/omemo/queue.dart';
-import 'package:test/test.dart';
-
-Future<void> testMethod(
-  RatchetAccessQueue queue,
-  List<String> data,
-  int duration,
-) async {
-  await queue.enterCriticalSection(data);
-
-  await Future<void>.delayed(Duration(seconds: duration));
-
-  await queue.leaveCriticalSection(data);
-}
-
-void main() {
-  test('Test blocking due to conflicts', () async {
-    final queue = RatchetAccessQueue();
-
-    unawaited(testMethod(queue, ['a', 'b', 'c'], 5));
-    unawaited(testMethod(queue, ['a'], 4));
-
-    await Future<void>.delayed(const Duration(seconds: 1));
-    expect(
-      queue.runningOperations.containsAll(['a', 'b', 'c']),
-      isTrue,
-    );
-    expect(queue.runningOperations.length, 3);
-
-    await Future<void>.delayed(const Duration(seconds: 4));
-
-    expect(
-      queue.runningOperations.containsAll(['a']),
-      isTrue,
-    );
-    expect(queue.runningOperations.length, 1);
-
-    await Future<void>.delayed(const Duration(seconds: 4));
-    expect(queue.runningOperations.length, 0);
-  });
-
-  test('Test not blocking due to no conflicts', () async {
-    final queue = RatchetAccessQueue();
-
-    unawaited(testMethod(queue, ['a', 'b'], 5));
-    unawaited(testMethod(queue, ['c'], 5));
-    unawaited(testMethod(queue, ['d'], 5));
-
-    await Future<void>.delayed(const Duration(seconds: 1));
-    expect(queue.runningOperations.length, 4);
-    expect(
-      queue.runningOperations.containsAll([
-        'a',
-        'b',
-        'c',
-        'd',
-      ]),
-      isTrue,
-    );
-  });
-}

test/serialisation_test.dart

@@ -0,0 +1,155 @@
+import 'dart:convert';
+import 'package:omemo_dart/omemo_dart.dart';
+import 'package:omemo_dart/src/trust/always.dart';
+import 'package:test/test.dart';
+
+Map<String, dynamic> jsonify(Map<String, dynamic> map) {
+  return jsonDecode(jsonEncode(map)) as Map<String, dynamic>;
+}
+
+void main() {
+  test('Test serialising and deserialising the Device', () async {
+    // Generate a random session
+    final oldSession = await OmemoSessionManager.generateNewIdentity(
+      'user@test.server',
+      AlwaysTrustingTrustManager(),
+      opkAmount: 1,
+    );
+    final oldDevice = await oldSession.getDevice();
+    final serialised = jsonify(await oldDevice.toJson());
+
+    final newDevice = OmemoDevice.fromJson(serialised);
+    expect(await oldDevice.equals(newDevice), true);
+  });
+
+  test('Test serialising and deserialising the Device after rotating the SPK',
+      () async {
+    // Generate a random session
+    final oldSession = await OmemoSessionManager.generateNewIdentity(
+      'user@test.server',
+      AlwaysTrustingTrustManager(),
+      opkAmount: 1,
+    );
+    final oldDevice =
+        await (await oldSession.getDevice()).replaceSignedPrekey();
+    final serialised = jsonify(await oldDevice.toJson());
+
+    final newDevice = OmemoDevice.fromJson(serialised);
+    expect(await oldDevice.equals(newDevice), true);
+  });
+
+  test('Test serialising and deserialising the OmemoDoubleRatchet', () async {
+    // Generate a random ratchet
+    const aliceJid = 'alice@server.example';
+    const bobJid = 'bob@other.server.example';
+    final aliceSession = await OmemoSessionManager.generateNewIdentity(
+      aliceJid,
+      AlwaysTrustingTrustManager(),
+      opkAmount: 1,
+    );
+    final bobSession = await OmemoSessionManager.generateNewIdentity(
+      bobJid,
+      AlwaysTrustingTrustManager(),
+      opkAmount: 1,
+    );
+    final aliceMessage = await aliceSession.encryptToJid(
+      bobJid,
+      'Hello Bob!',
+      newSessions: [
+        await bobSession.getDeviceBundle(),
+      ],
+    );
+    await bobSession.decryptMessage(
+      aliceMessage.ciphertext,
+      aliceJid,
+      await aliceSession.getDeviceId(),
+      aliceMessage.encryptedKeys,
+      getTimestamp(),
+    );
+    final aliceOld =
+        aliceSession.getRatchet(bobJid, await bobSession.getDeviceId());
+    final aliceSerialised = jsonify(await aliceOld.toJson());
+    final aliceNew = OmemoDoubleRatchet.fromJson(aliceSerialised);
+
+    expect(await aliceOld.equals(aliceNew), true);
+  });
+
+  test('Test serialising and deserialising the OmemoSessionManager', () async {
+    // Generate a random session
+    final oldSession = await OmemoSessionManager.generateNewIdentity(
+      'a@server',
+      AlwaysTrustingTrustManager(),
+      opkAmount: 4,
+    );
+    final bobSession = await OmemoSessionManager.generateNewIdentity(
+      'b@other.server',
+      AlwaysTrustingTrustManager(),
+      opkAmount: 4,
+    );
+    await oldSession.addSessionFromBundle(
+      'bob@localhost',
+      await bobSession.getDeviceId(),
+      await bobSession.getDeviceBundle(),
+    );
+
+    // Serialise and deserialise
+    final serialised = jsonify(await oldSession.toJsonWithoutSessions());
+    final newSession = OmemoSessionManager.fromJsonWithoutSessions(
+      serialised,
+      // NOTE: At this point, we don't care about this attribute
+      {},
+      AlwaysTrustingTrustManager(),
+    );
+
+    final oldDevice = await oldSession.getDevice();
+    final newDevice = await newSession.getDevice();
+    expect(await oldDevice.equals(newDevice), true);
+    expect(await oldSession.getDeviceMap(), await newSession.getDeviceMap());
+  });
+
+  test('Test serializing and deserializing RatchetMapKey', () {
+    const test1 = RatchetMapKey('user@example.org', 1234);
+    final result1 = RatchetMapKey.fromJsonKey(test1.toJsonKey());
+    expect(result1.jid, test1.jid);
+    expect(result1.deviceId, test1.deviceId);
+
+    const test2 = RatchetMapKey('user@example.org/hallo:welt', 3333);
+    final result2 = RatchetMapKey.fromJsonKey(test2.toJsonKey());
+    expect(result2.jid, test2.jid);
+    expect(result2.deviceId, test2.deviceId);
+  });
+
+  test('Test serializing and deserializing the components of the BTBV manager',
+      () async {
+    // Caroline's BTBV manager
+    final btbv = MemoryBTBVTrustManager();
+    // Example data
+    const aliceJid = 'alice@some.server';
+    const bobJid = 'bob@other.server';
+
+    await btbv.onNewSession(aliceJid, 1);
+    await btbv.setDeviceTrust(aliceJid, 1, BTBVTrustState.verified);
+    await btbv.onNewSession(aliceJid, 2);
+    await btbv.onNewSession(bobJid, 3);
+    await btbv.onNewSession(bobJid, 4);
+
+    final serialized = jsonify(await btbv.toJson());
+    final deviceList =
+        BlindTrustBeforeVerificationTrustManager.deviceListFromJson(
+      serialized,
+    );
+    expect(btbv.devices, deviceList);
+
+    final trustCache =
+        BlindTrustBeforeVerificationTrustManager.trustCacheFromJson(
+      serialized,
+    );
+    expect(btbv.trustCache, trustCache);
+
+    final enableCache =
+        BlindTrustBeforeVerificationTrustManager.enableCacheFromJson(
+      serialized,
+    );
+    expect(btbv.enablementCache, enableCache);
+  });
+}

test/trust_test.dart

@@ -4,7 +4,7 @@ import 'package:test/test.dart';
 void main() {
   test('Test the Blind Trust Before Verification TrustManager', () async {
     // Caroline's BTBV manager
-    final btbv = BlindTrustBeforeVerificationTrustManager();
+    final btbv = MemoryBTBVTrustManager();
     // Example data
     const aliceJid = 'alice@some.server';
     const bobJid = 'bob@other.server';

test/x3dh_test.dart

@@ -26,8 +26,7 @@ void main() {
     );
 
     // Alice does X3DH
-    final resultAliceRaw = await x3dhFromBundle(bundleBob, ikAlice);
-    final resultAlice = resultAliceRaw.get<X3DHAliceResult>();
+    final resultAlice = await x3dhFromBundle(bundleBob, ikAlice);
 
     // Alice sends the inital message to Bob
     // ...
@@ -69,7 +68,18 @@ void main() {
     );
 
     // Alice does X3DH
-    final result = await x3dhFromBundle(bundleBob, ikAlice);
-    expect(result.isType<InvalidKeyExchangeSignatureError>(), isTrue);
+    var exception = false;
+    try {
+      await x3dhFromBundle(bundleBob, ikAlice);
+    } catch (e) {
+      exception = true;
+      expect(
+        e is InvalidSignatureException,
+        true,
+        reason: 'Expected InvalidSignatureException, but got $e',
+      );
+    }
+
+    expect(exception, true, reason: 'Expected test failure');
   });
 }