fix import cycle with asymmetricpadding (#5758)

* fix import cycle with asymmetricpadding

* Update src/cryptography/hazmat/primitives/_asymmetric.py

src/cryptography/hazmat/primitives/_asymmetric.py

@@ -0,0 +1,17 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+import abc
+
+
+# This exists to break an import cycle. It is normally accessible from the
+# asymmetric padding module.
+
+
+class AsymmetricPadding(metaclass=abc.ABCMeta):
+    @abc.abstractproperty
+    def name(self) -> str:
+        """
+        A string naming this padding (e.g. "PSS", "PKCS1").
+        """

src/cryptography/hazmat/primitives/asymmetric/padding.py

@@ -3,21 +3,13 @@
 # for complete details.
 
 
-import abc
 import typing
 
 from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives._asymmetric import AsymmetricPadding
 from cryptography.hazmat.primitives.asymmetric import rsa
 
 
-class AsymmetricPadding(metaclass=abc.ABCMeta):
-    @abc.abstractproperty
-    def name(self) -> str:
-        """
-        A string naming this padding (e.g. "PSS", "PKCS1").
-        """
-
-
 class PKCS1v15(AsymmetricPadding):
     name = "EMSA-PKCS1-v1_5"
 

src/cryptography/hazmat/primitives/asymmetric/rsa.py

@@ -12,12 +12,12 @@
 from cryptography.hazmat.backends import _get_backend
 from cryptography.hazmat.backends.interfaces import RSABackend
 from cryptography.hazmat.primitives import _serialization, hashes
+from cryptography.hazmat.primitives._asymmetric import AsymmetricPadding
 from cryptography.hazmat.primitives.asymmetric import (
     AsymmetricSignatureContext,
     AsymmetricVerificationContext,
     utils as asym_utils,
 )
-from cryptography.hazmat.primitives.asymmetric.padding import AsymmetricPadding
 
 
 class RSAPrivateKey(metaclass=abc.ABCMeta):