diff --git a/tests/test_utility.py b/tests/test_utility.py
index db9d8fe8..5dcd77ce 100644
--- a/tests/test_utility.py
+++ b/tests/test_utility.py
@@ -48,3 +48,38 @@ def example_function(*args, **kwargs):
         mock_is_github_ip.assert_called_once()
         self.assertEqual(mock_abort.call_count, 7)
         self.assertEqual(response, "Test Success")
+
+    def test_is_valid_signature(self):
+        """Test is_valid_signature with valid and invalid inputs."""
+        import hashlib
+        import hmac
+        from utility import is_valid_signature
+
+        key = "secret_key_123"
+        payload = b'{"ref": "refs/heads/master"}'
+        mac = hmac.new(b"secret_key_123", payload, hashlib.sha256)
+        valid_header = f"sha256={mac.hexdigest()}"
+
+        # Valid signature with bytes and str payload
+        self.assertTrue(is_valid_signature(valid_header, payload, key))
+        self.assertTrue(
+            is_valid_signature(valid_header, payload.decode(), key))
+
+        # Invalid signatures / tamper
+        self.assertFalse(is_valid_signature("sha256=wrong", payload, key))
+
+        # Missing or invalid signature formats
+        self.assertFalse(is_valid_signature(None, payload, key))
+        self.assertFalse(is_valid_signature("", payload, key))
+        self.assertFalse(is_valid_signature(12345, payload, key))
+        self.assertFalse(is_valid_signature("no_equal_sign", payload, key))
+
+        # Unknown or non-callable algorithms
+        self.assertFalse(is_valid_signature("unknown=1234", payload, key))
+        self.assertFalse(is_valid_signature("__dict__=1234", payload, key))
+        self.assertFalse(
+            is_valid_signature("algorithms_guaranteed=1", payload, key))
+
+        # None data or key
+        self.assertFalse(is_valid_signature(valid_header, None, key))
+        self.assertFalse(is_valid_signature(valid_header, payload, None))
diff --git a/utility.py b/utility.py
index ecc8df7e..fdd70990 100644
--- a/utility.py
+++ b/utility.py
@@ -156,13 +156,42 @@ def is_valid_signature(x_hub_signature, data, private_key):
     :param x_hub_signature: Signature to check
     :type x_hub_signature: str
     :param data: Signature's data
-    :type data: bytearray
+    :type data: bytearray or bytes or str
     :param private_key: Signature's token
-    :type private_key: str
+    :type private_key: str or bytes
     """
+    if not x_hub_signature or not isinstance(x_hub_signature, str):
+        return False
+
+    if '=' not in x_hub_signature:
+        return False
+
     hash_algorithm, github_signature = x_hub_signature.split('=', 1)
-    algorithm = hashlib.__dict__.get(hash_algorithm)
-    encoded_key = bytes(private_key, 'latin-1')
-    mac = hmac.new(encoded_key, msg=data, digestmod=algorithm)
+    hash_algorithm = hash_algorithm.lower()
+
+    if hash_algorithm not in hashlib.algorithms_available:
+        return False
+
+    algorithm = getattr(hashlib, hash_algorithm, None)
+    if not callable(algorithm):
+        return False
 
-    return hmac.compare_digest(mac.hexdigest(), github_signature)
+    if private_key is None:
+        return False
+    if isinstance(private_key, str):
+        encoded_key = private_key.encode('latin-1')
+    elif isinstance(private_key, (bytes, bytearray)):
+        encoded_key = bytes(private_key)
+    else:
+        return False
+
+    if data is None:
+        return False
+    if isinstance(data, str):
+        data = data.encode('utf-8')
+
+    try:
+        mac = hmac.new(encoded_key, msg=data, digestmod=algorithm)
+        return hmac.compare_digest(mac.hexdigest(), github_signature)
+    except (ValueError, TypeError):
+        return False