feat: Allow calculating fingerprints

lib/omemo_dart.dart

@@ -7,5 +7,6 @@ export 'src/helpers.dart';
 export 'src/keys.dart';
 export 'src/omemo/bundle.dart';
 export 'src/omemo/device.dart';
+export 'src/omemo/fingerprint.dart';
 export 'src/omemo/sessionmanager.dart';
 export 'src/x3dh/x3dh.dart';

lib/src/double_ratchet/double_ratchet.dart

@@ -65,8 +65,9 @@ class OmemoDoubleRatchet {
     this.ns,  // Ns
     this.nr,  // Nr
     this.pn,  // Pn
+    this.ik,
     this.sessionAd,
-    this.mkSkipped,
+    this.mkSkipped, // MKSKIPPED
   );
 
   factory OmemoDoubleRatchet.fromJson(Map<String, dynamic> data) {
@@ -81,6 +82,7 @@ class OmemoDoubleRatchet {
       'ns': 0,
       'nr': 0,
       'pn': 0,
+      'ik_pub': 'base/64/encoded',
       'session_ad': 'base/64/encoded',
       'mkskipped': [
         {
@@ -110,6 +112,10 @@ class OmemoDoubleRatchet {
       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,
     );
@@ -135,14 +141,18 @@ class OmemoDoubleRatchet {
   /// Previous sending chain number
   int pn;
 
+  /// The IK public key from the chat partner. Not used for the actual encryption but
+  /// for verification purposes
+  final OmemoPublicKey ik;
+  
   final List<int> sessionAd;
 
   final Map<SkippedKey, List<int>> mkSkipped;
 
   /// Create an OMEMO session using the Signed Pre Key [spk], the shared secret [sk] that
   /// was obtained using a X3DH and the associated data [ad] that was also obtained through
-  /// a X3DH.
+  /// a X3DH. [ik] refers to Bob's (the receiver's) IK public key.
-  static Future<OmemoDoubleRatchet> initiateNewSession(OmemoPublicKey spk, List<int> sk, List<int> ad) async {
+  static Future<OmemoDoubleRatchet> initiateNewSession(OmemoPublicKey spk, OmemoPublicKey ik, List<int> sk, List<int> ad) async {
     final dhs = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
     final dhr = spk;
     final rk  = await kdfRk(sk, await omemoDH(dhs, dhr, 0));
@@ -157,6 +167,7 @@ class OmemoDoubleRatchet {
       0,
       0,
       0,
+      ik,
       ad,
       {},
     );
@@ -164,8 +175,9 @@ class OmemoDoubleRatchet {
 
   /// Create an OMEMO session that was not initiated by the caller using the used Signed
   /// Pre Key keypair [spk], the shared secret [sk] that was obtained through a X3DH and
-  /// the associated data [ad] that was also obtained through a X3DH.
+  /// the associated data [ad] that was also obtained through a X3DH. [ik] refers to
-  static Future<OmemoDoubleRatchet> acceptNewSession(OmemoKeyPair spk, List<int> sk, List<int> ad) async {
+  /// Alice's (the initiator's) IK public key.
+  static Future<OmemoDoubleRatchet> acceptNewSession(OmemoKeyPair spk, OmemoPublicKey ik, List<int> sk, List<int> ad) async {
     return OmemoDoubleRatchet(
       spk,
       null,
@@ -175,6 +187,7 @@ class OmemoDoubleRatchet {
       0,
       0,
       0,
+      ik,
       ad,
       {},
     );
@@ -199,6 +212,7 @@ class OmemoDoubleRatchet {
       'ns': ns,
       'nr': nr,
       'pn': pn,
+      'ik_pub': base64.encode(await ik.getBytes()),
       'session_ad': base64.encode(sessionAd),
       'mkskipped': mkSkippedSerialised,
     };
@@ -302,7 +316,12 @@ class OmemoDoubleRatchet {
     final cksMatch = cks == null ? other.cks == null : listsEqual(cks!, other.cks!);
  
     // ignore: invalid_use_of_visible_for_testing_member
-    return await dhs.equals(other.dhs) &&
+    final dhsMatch = await dhs.equals(other.dhs);
+    // ignore: invalid_use_of_visible_for_testing_member
+    final ikMatch = await ik.equals(other.ik);
+    
+    return dhsMatch &&
+      ikMatch &&
       dhrMatch &&
       listsEqual(rk, other.rk) &&
       cksMatch &&

lib/src/omemo/fingerprint.dart

@@ -0,0 +1,19 @@
+import 'package:meta/meta.dart';
+
+@immutable
+class DeviceFingerprint {
+
+  const DeviceFingerprint(this.deviceId, this.fingerprint);
+  final String fingerprint;
+  final int deviceId;
+
+  @override
+  bool operator ==(Object other) {
+    return other is DeviceFingerprint &&
+      fingerprint == other.fingerprint &&
+      deviceId == other.deviceId;
+  }
+
+  @override
+  int get hashCode => fingerprint.hashCode ^ deviceId.hashCode;
+}

lib/src/omemo/sessionmanager.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 import 'dart:convert';
 import 'package:collection/collection.dart';
 import 'package:cryptography/cryptography.dart';
+import 'package:hex/hex.dart';
 import 'package:meta/meta.dart';
 import 'package:omemo_dart/src/crypto.dart';
 import 'package:omemo_dart/src/double_ratchet/double_ratchet.dart';
@@ -11,6 +12,7 @@ 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/device.dart';
+import 'package:omemo_dart/src/omemo/fingerprint.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';
@@ -19,7 +21,6 @@ import 'package:synchronized/synchronized.dart';
 
 /// The info used for when encrypting the AES key for the actual payload.
 const omemoPayloadInfoString = 'OMEMO Payload';
-
 @immutable
 class EncryptionResult {
 
@@ -158,6 +159,7 @@ class OmemoSessionManager {
     );
     final ratchet = await OmemoDoubleRatchet.initiateNewSession(
       bundle.spk,
+      bundle.ik,
       kexResult.sk,
       kexResult.ad,
     );
@@ -187,6 +189,7 @@ class OmemoSessionManager {
     );
     final ratchet = await OmemoDoubleRatchet.acceptNewSession(
       device.spk,
+      OmemoPublicKey.fromBytes(kex.ik!, KeyPairType.ed25519),
       kexResult.sk,
       kexResult.ad,
     );
@@ -327,6 +330,29 @@ class OmemoSessionManager {
     return utf8.decode(plaintext);
   }
 
+  /// Returns the list of hex-encoded fingerprints we have for sessions with [jid].
+  Future<List<DeviceFingerprint>> getHexFingerprintsForJid(String jid) async {
+    final fingerprints = List<DeviceFingerprint>.empty(growable: true);
+
+    await _lock.synchronized(() async {
+      // Get devices for jid
+      final devices = _deviceMap[jid]!;
+
+      for (final deviceId in devices) {
+        final ratchet = _ratchetMap[RatchetMapKey(jid, deviceId)]!;
+
+        fingerprints.add(
+          DeviceFingerprint(
+            deviceId,
+            HEX.encode(await ratchet.ik.getBytes()),
+          ),
+        );
+      }
+    });
+
+    return fingerprints;
+  }
+  
   @visibleForTesting
   OmemoDoubleRatchet getRatchet(String jid, int deviceId) => _ratchetMap[RatchetMapKey(jid, deviceId)]!;
 

pubspec.yaml

@@ -8,6 +8,7 @@ environment:
 dependencies:
   collection: ^1.16.0
   cryptography: ^2.0.5
+  hex: ^0.2.0
   pinenacl: ^0.5.1
   synchronized: ^3.0.0+2
 

test/double_ratchet_test.dart

@@ -79,11 +79,13 @@ void main() {
     // Build a session
     final alicesRatchet = await OmemoDoubleRatchet.initiateNewSession(
       spkBob.pk,
+      ikBob.pk,
       resultAlice.sk,
       resultAlice.ad,
     );
     final bobsRatchet = await OmemoDoubleRatchet.acceptNewSession(
       spkBob,
+      ikAlice.pk,
       resultBob.sk,
       resultBob.ad,
     );

test/omemo_test.dart

@@ -132,5 +132,15 @@ void main() {
       bobResponseMessage.encryptedKeys,
     );
     expect(bobResponseText, aliceReceivedMessage);
+
+    // Alice checks the fingerprints
+    final fingerprints = await aliceSession.getHexFingerprintsForJid(bobJid);
+    // Check that they the fingerprints are correct
+    expect(fingerprints.length, 2);
+    expect(fingerprints[0] != fingerprints[1], true);
+    // Check that those two calls do not throw an exception
+    aliceSession
+      ..getRatchet(bobJid, fingerprints[0].deviceId)
+      ..getRatchet(bobJid, fingerprints[1].deviceId);
   });
 }