Handle load_pem_public_key ValueError (#952)

* Handle load_pem_public_key ValueError

* Add test for invalid key errors on prepare_key of an invalid key

---------

Co-authored-by: MVRA <61065@icf.com>

jwt/algorithms.py

@@ -21,7 +21,7 @@
 )
 
 try:
-    from cryptography.exceptions import InvalidSignature
+    from cryptography.exceptions import InvalidSignature, UnsupportedAlgorithm
     from cryptography.hazmat.backends import default_backend
     from cryptography.hazmat.primitives import hashes
     from cryptography.hazmat.primitives.asymmetric import padding
@@ -343,7 +343,10 @@ def prepare_key(self, key: AllowedRSAKeys | str | bytes) -> AllowedRSAKeys:
                         RSAPrivateKey, load_pem_private_key(key_bytes, password=None)
                     )
             except ValueError:
-                return cast(RSAPublicKey, load_pem_public_key(key_bytes))
+                try:
+                    return cast(RSAPublicKey, load_pem_public_key(key_bytes))
+                except (ValueError, UnsupportedAlgorithm):
+                    raise InvalidKeyError("Could not parse the provided public key.")
 
         @overload
         @staticmethod

tests/test_algorithms.py

@@ -1100,3 +1100,14 @@ def test_hmac_can_compute_digest(self):
         algo = HMACAlgorithm(HMACAlgorithm.SHA256)
         computed_hash = algo.compute_hash_digest(b"foo")
         assert computed_hash == foo_hash
+
+    @crypto_required
+    def test_rsa_prepare_key_raises_invalid_key_error_on_invalid_pem(self):
+        algo = RSAAlgorithm(RSAAlgorithm.SHA256)
+        invalid_key = "invalid key"
+
+        with pytest.raises(InvalidKeyError) as excinfo:
+            algo.prepare_key(invalid_key)
+
+        # Check that the exception message is correct
+        assert "Could not parse the provided public key." in str(excinfo.value)