Cross-signing: Detect when cross-signing keys have been changed

Riot/Modules/Application/LegacyAppDelegate.m

@@ -227,6 +227,8 @@ NSString *const AppDelegateUniversalLinkDidChangeNotification = @"AppDelegateUni
 @property (nonatomic, weak) id userDidSignInOnNewDeviceObserver;
 @property (weak, nonatomic) UIAlertController *userNewSignInAlertController;
 
+@property (nonatomic, weak) id userDidChangeCrossSigningKeysObserver;
+
 /**
  Related push notification service instance. Will be created when launch finished.
  */
@@ -1773,6 +1775,8 @@ NSString *const AppDelegateUniversalLinkDidChangeNotification = @"AppDelegateUni
             // Register to user new device sign in notification
             [self registerUserDidSignInOnNewDeviceNotificationForSession:mxSession];
             
+            [self registerDidChangeCrossSigningKeysNotificationForSession:mxSession];
+            
             // Register to new key verification request
             [self registerNewRequestNotificationForSession:mxSession];
             
@@ -4263,6 +4267,29 @@ NSString *const AppDelegateUniversalLinkDidChangeNotification = @"AppDelegateUni
     self.userNewSignInAlertController = alert;
 }
 
+
+#pragma mark - Cross-signing reset detection
+
+- (void)registerDidChangeCrossSigningKeysNotificationForSession:(MXSession*)session
+{
+    MXCrossSigning *crossSigning = session.crypto.crossSigning;
+    
+    if (!crossSigning)
+    {
+        return;
+    }
+    
+    self.userDidChangeCrossSigningKeysObserver = [NSNotificationCenter.defaultCenter addObserverForName:MXCrossSigningDidChangeCrossSigningKeysNotification
+                                                                                            object:crossSigning
+                                                                                             queue:[NSOperationQueue mainQueue]
+                                                                                        usingBlock:^(NSNotification *notification)
+                                             {
+        NSLog(@"[AppDelegate] registerDidChangeCrossSigningKeysNotificationForSession");
+        [self.masterTabBarController presentVerifyCurrentSessionAlertIfNeededWithSession:session];
+    }];
+}
+
+
 #pragma mark - Complete security
 
 - (BOOL)presentCompleteSecurityForSession:(MXSession*)mxSession