additional validation of received secrets

lib/src/client.dart

@@ -97,8 +97,8 @@ class Client {
   /// enableE2eeRecovery: Enable additional logic to try to recover from bad e2ee sessions
   Client(this.clientName,
       {this.debug = false, this.database, this.enableE2eeRecovery = false}) {
-    keyManager = KeyManager(this);
     ssss = SSSS(this);
+    keyManager = KeyManager(this);
     crossSigning = CrossSigning(this);
     onLoginStateChanged.stream.listen((loginState) {
       print('LoginState: ${loginState.toString()}');

lib/src/cross_signing.dart

@@ -12,7 +12,28 @@ const MASTER_KEY = 'm.cross_signing.master';
 
 class CrossSigning {
   final Client client;
-  CrossSigning(this.client);
+  CrossSigning(this.client) {
+    client.ssss.setValidator(SELF_SIGNING_KEY, (String secret) async {
+      final keyObj = olm.PkSigning();
+      try {
+        return keyObj.init_with_seed(base64.decode(secret)) == client.userDeviceKeys[client.userID].selfSigningKey.ed25519Key;
+      } catch (_) {
+        return false;
+      } finally {
+        keyObj.free();
+      }
+    });
+    client.ssss.setValidator(USER_SIGNING_KEY, (String secret) async {
+      final keyObj = olm.PkSigning();
+      try {
+        return keyObj.init_with_seed(base64.decode(secret)) == client.userDeviceKeys[client.userID].userSigningKey.ed25519Key;
+      } catch (_) {
+        return false;
+      } finally {
+        keyObj.free();
+      }
+    });
+  }
 
   bool get enabled =>
       client.accountData[SELF_SIGNING_KEY] != null &&

lib/src/key_manager.dart

@@ -15,7 +15,19 @@ class KeyManager {
   final outgoingShareRequests = <String, KeyManagerKeyShareRequest>{};
   final incomingShareRequests = <String, KeyManagerKeyShareRequest>{};
 
-  KeyManager(this.client);
+  KeyManager(this.client) {
+    client.ssss.setValidator(MEGOLM_KEY, (String secret) async {
+      final keyObj = olm.PkDecryption();
+      try {
+        final info = await getRoomKeysInfo();
+        return keyObj.init_with_private_key(base64.decode(secret)) == info['auth_data']['public_key'];
+      } catch (_) {
+        return false;
+      } finally {
+        keyObj.free();
+      }
+    });
+  }
 
   bool get enabled => client.accountData[MEGOLM_KEY] != null;
 
@@ -42,15 +54,13 @@ class KeyManager {
     }
     final privateKey = base64.decode(await client.ssss.getCached(MEGOLM_KEY));
     final decryption = olm.PkDecryption();
+    final info = await getRoomKeysInfo();
     String backupPubKey;
     try {
       backupPubKey = decryption.init_with_private_key(privateKey);
-    } catch (_) {
-      decryption.free();
-      rethrow;
-    }
-    if (backupPubKey == null) {
-      decryption.free();
+
+      if (backupPubKey == null || !info.containsKey('auth_data') || !(info['auth_data'] is Map) || info['auth_data']['public_key'] != backupPubKey) {
+        
         return;
       }
       // TODO: check if pubkey is valid
@@ -87,6 +97,9 @@ class KeyManager {
           }
         }
       }
+    } finally {
+      decryption.free();
+    }
   }
 
   Future<void> loadSingleKey(String roomId, String sessionId) async {

lib/src/ssss.dart

@@ -27,6 +27,7 @@ const OLM_PRIVATE_KEY_LENGTH = 32; // TODO: fetch from dart-olm
 class SSSS {
   final Client client;
   final pendingShareRequests = <String, _ShareRequest>{};
+  final _validators = <String, Future<bool> Function(String)>{};
   SSSS(this.client);
 
   static _DerivedKeys deriveKeys(Uint8List key, String name) {
@@ -119,6 +120,10 @@ class SSSS {
         info.iterations, info.bits != null ? info.bits / 8 : 32));
   }
 
+  void setValidator(String type, Future<bool> Function(String) validator) {
+    _validators[type] = validator;
+  }
+
   String get defaultKeyId {
     final keyData = client.accountData['m.secret_storage.default_key'];
     if (keyData == null || !(keyData.content['key'] is String)) {
@@ -312,11 +317,17 @@ class SSSS {
         print('[SSSS] Someone else replied?');
         return; // someone replied whom we didn't send the share request to
       }
-      pendingShareRequests.remove(request.requestId);
+      final secret = event.content['secret'];
       if (!(event.content['secret'] is String)) {
         print('[SSSS] Secret wasn\'t a string');
         return; // the secret wasn't a string....wut?
       }
+      // let's validate if the secret is, well, valid
+      if (_validators.containsKey(request.type) && !(await _validators[request.type](secret))) {
+        print('[SSSS] The received secret was invalid');
+        return; // didn't pass the validator
+      }
+      pendingShareRequests.remove(request.requestId);
       if (request.start.add(Duration(minutes: 15)).isBefore(DateTime.now())) {
         print('[SSSS] Request is too far in the past');
         return; // our request is more than 15min in the past...better not trust it anymore
@@ -326,7 +337,7 @@ class SSSS {
         final keyId = keyIdFromType(request.type);
         if (keyId != null) {
           await client.database.storeSSSSCache(
-              client.id, request.type, keyId, event.content['secret']);
+              client.id, request.type, keyId, secret);
         }
       }
     }