diff --git a/lib/encryption/olm_manager.dart b/lib/encryption/olm_manager.dart
index 1c2cac7..9635939 100644
--- a/lib/encryption/olm_manager.dart
+++ b/lib/encryption/olm_manager.dart
@@ -24,6 +24,7 @@ import 'package:famedlysdk/matrix_api.dart';
 import 'package:olm/olm.dart' as olm;
 import 'package:pedantic/pedantic.dart';
 
+import '../encryption/utils/json_signature_check_extension.dart';
 import '../src/utils/logs.dart';
 import 'encryption.dart';
 import 'utils/olm_session.dart';
@@ -75,7 +76,8 @@ class OlmManager {
     }
   }
 
-  /// Adds a signature to this json from this olm account.
+  /// Adds a signature to this json from this olm account and returns the signed
+  /// json.
   Map<String, dynamic> signJson(Map<String, dynamic> payload) {
     if (!enabled) throw ('Encryption is disabled');
     final Map<String, dynamic> unsigned = payload['unsigned'];
@@ -105,6 +107,7 @@ class OlmManager {
   }
 
   /// Checks the signature of a signed json object.
+  @deprecated
   bool checkJsonSignature(String key, Map<String, dynamic> signedJson,
       String userId, String deviceId) {
     if (!enabled) throw ('Encryption is disabled');
@@ -406,8 +409,7 @@ class OlmManager {
         final identityKey =
             client.userDeviceKeys[userId].deviceKeys[deviceId].curve25519Key;
         for (Map<String, dynamic> deviceKey in deviceKeysEntry.value.values) {
-          if (!checkJsonSignature(
-              fingerprintKey, deviceKey, userId, deviceId)) {
+          if (!deviceKey.checkJsonSignature(fingerprintKey, userId, deviceId)) {
             continue;
           }
           var session = olm.Session();
diff --git a/lib/encryption/utils/json_signature_check_extension.dart b/lib/encryption/utils/json_signature_check_extension.dart
new file mode 100644
index 0000000..8a2401f
--- /dev/null
+++ b/lib/encryption/utils/json_signature_check_extension.dart
@@ -0,0 +1,29 @@
+import 'package:canonical_json/canonical_json.dart';
+import 'package:famedlysdk/src/utils/logs.dart';
+import 'package:olm/olm.dart' as olm;
+
+extension JsonSignatureCheckExtension on Map<String, dynamic> {
+  /// Checks the signature of a signed json object.
+  bool checkJsonSignature(String key, String userId, String deviceId) {
+    final Map<String, dynamic> signatures = this['signatures'];
+    if (signatures == null || !signatures.containsKey(userId)) return false;
+    remove('unsigned');
+    remove('signatures');
+    if (!signatures[userId].containsKey('ed25519:$deviceId')) return false;
+    final String signature = signatures[userId]['ed25519:$deviceId'];
+    final canonical = canonicalJson.encode(this);
+    final message = String.fromCharCodes(canonical);
+    var isValid = false;
+    final olmutil = olm.Utility();
+    try {
+      olmutil.ed25519_verify(key, message, signature);
+      isValid = true;
+    } catch (e, s) {
+      isValid = false;
+      Logs.error('[LibOlm] Signature check failed: ' + e.toString(), s);
+    } finally {
+      olmutil.free();
+    }
+    return isValid;
+  }
+}
diff --git a/test/encryption/olm_manager_test.dart b/test/encryption/olm_manager_test.dart
index 78e7068..883171c 100644
--- a/test/encryption/olm_manager_test.dart
+++ b/test/encryption/olm_manager_test.dart
@@ -21,6 +21,7 @@ import 'package:famedlysdk/famedlysdk.dart';
 import 'package:famedlysdk/src/utils/logs.dart';
 import 'package:test/test.dart';
 import 'package:olm/olm.dart' as olm;
+import 'package:famedlysdk/encryption/utils/json_signature_check_extension.dart';
 
 import '../fake_client.dart';
 import '../fake_matrix_api.dart';
@@ -51,13 +52,9 @@ void main() {
       };
       final signedPayload = client.encryption.olmManager.signJson(payload);
       expect(
-          client.encryption.olmManager.checkJsonSignature(client.fingerprintKey,
-              signedPayload, client.userID, client.deviceID),
+          signedPayload.checkJsonSignature(
+              client.fingerprintKey, client.userID, client.deviceID),
           true);
-      expect(
-          client.encryption.olmManager.checkJsonSignature(
-              client.fingerprintKey, payload, client.userID, client.deviceID),
-          false);
     });
 
     test('uploadKeys', () async {