feat: Add managing our own keys

lib/src/helpers.dart

@@ -34,3 +34,8 @@ List<int> generateRandomBytes(int length) {
 
   return bytes;
 }
+
+/// Generate a random number between 0 inclusive and 2**32 exclusive (2**32 - 1 inclusive).
+int generateRandom32BitNumber() {
+  return Random.secure().nextInt(4294967295 /*pow(2, 32) - 1*/);
+}

lib/src/omemo/device.dart

@@ -0,0 +1,101 @@
+import 'dart:convert';
+import 'package:cryptography/cryptography.dart';
+import 'package:meta/meta.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/x3dh/x3dh.dart';
+
+/// This class represents an OmemoBundle but with all keypairs belonging to the keys
+@immutable
+class Device {
+
+  const Device(this.id, this.ik, this.spk, this.spkId, this.spkSignature, this.opks);
+
+  /// Generate a completely new device, i.e. cryptographic identity.
+  static Future<Device> generateNewDevice({ int opkAmount = 100 }) async {
+    final id = generateRandom32BitNumber();
+    final ik = await OmemoKeyPair.generateNewPair(KeyPairType.ed25519);
+    final spk = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
+    final spkId = generateRandom32BitNumber();
+    final signature = await sig(ik, await spk.pk.getBytes());
+
+    final opks = <String, OmemoKeyPair>{};
+    for (var i = 0; i < opkAmount; i++) {
+      opks[i.toString()] = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
+    }
+
+    return Device(id.toString(), ik, spk, spkId.toString(), signature, opks);
+  }
+  
+  /// The device Id
+  final String id;
+
+  /// The identity key
+  final OmemoKeyPair ik;
+
+  /// The signed prekey...
+  final OmemoKeyPair spk;
+  /// ...its Id, ...
+  final String spkId;
+  /// ...and its signature
+  final List<int> spkSignature;
+
+  /// Map of an id to the associated Onetime-Prekey
+  final Map<String, OmemoKeyPair> opks;
+
+  /// This replaces the Onetime-Prekey with id [id] with a completely new one. Returns
+  /// a new Device object that copies over everything but replaces said key.
+  Future<Device> replaceOnetimePrekey(String id) async {
+    final newOpk = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
+
+    return Device(
+      id,
+      ik,
+      spk,
+      spkId,
+      spkSignature,
+      opks.map((keyId, opk) {
+        if (keyId == id) {
+          return MapEntry(id, newOpk);
+        }
+
+        return MapEntry(id, opk);
+      }),
+    );
+  }
+
+  /// This replaces the Signed-Prekey with a completely new one. Returns a new Device object
+  /// that copies over everything but replaces the Signed-Prekey and its signature.
+  Future<Device> replaceSignedPrekey() async {
+    final newSpk = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
+    final newSpkId = generateRandom32BitNumber();
+    final newSignature = await sig(ik, await newSpk.pk.getBytes());
+
+    return Device(
+      id,
+      ik,
+      newSpk,
+      newSpkId.toString(),
+      newSignature,
+      opks,
+    );
+  }
+
+  Future<OmemoBundle> toBundle() async {
+    final encodedOpks = <String, String>{};
+
+    for (final opkKey in opks.keys) {
+      encodedOpks[opkKey] = base64.encode(await opks[opkKey]!.pk.getBytes());
+    }
+
+    return OmemoBundle(
+      id,
+      base64.encode(await spk.pk.getBytes()),
+      spkId,
+      base64.encode(spkSignature),
+      base64.encode(await ik.pk.getBytes()),
+      encodedOpks,
+    );
+  }
+}

lib/src/omemo/sessionmanager.dart

@@ -2,6 +2,7 @@ import 'dart:convert';
 import 'package:omemo_dart/src/crypto.dart';
 import 'package:omemo_dart/src/double_ratchet/double_ratchet.dart';
 import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/omemo/device.dart';
 import 'package:synchronized/synchronized.dart';
 
 /// The info used for when encrypting the AES key for the actual payload.
@@ -21,7 +22,14 @@ class EncryptionResult {
 
 class OmemoSessionManager {
 
-  OmemoSessionManager() : _ratchetMap = {}, _deviceMap = {}, _lock = Lock();
+  OmemoSessionManager(this.device) : _ratchetMap = {}, _deviceMap = {}, _lock = Lock();
+
+  /// Generate a new cryptographic identity.
+  static Future<OmemoSessionManager> generateNewIdentity({ int opkAmount = 100 }) async {
+    final device = await Device.generateNewDevice(opkAmount: opkAmount);
+
+    return OmemoSessionManager(device);
+  }
   
   /// Lock for _ratchetMap and _bundleMap
   final Lock _lock;
@@ -32,6 +40,9 @@ class OmemoSessionManager {
   /// Mapping of a bare Jid to its Device Ids
   final Map<String, List<String>> _deviceMap;
 
+  /// Our own keys
+  Device device;
+
   /// Add a session [ratchet] with the [deviceId] to the internal tracking state.
   Future<void> addSession(String jid, String deviceId, OmemoDoubleRatchet ratchet) async {
     await _lock.synchronized(() async {