deprecate backend part 11 of n (#6530)

cipher class

3 files changed, 14 insertions, 32 deletions

diff --git a/src/cryptography/hazmat/primitives/ciphers/base.py b/src/cryptography/hazmat/primitives/ciphers/base.py
index 0ae519c6d..9b80421c2 100644
--- a/src/cryptography/hazmat/primitives/ciphers/base.py
+++ b/src/cryptography/hazmat/primitives/ciphers/base.py
@@ -11,11 +11,7 @@ from cryptography.exceptions import (
     AlreadyFinalized,
     AlreadyUpdated,
     NotYetFinalized,
-    UnsupportedAlgorithm,
-    _Reasons,
 )
-from cryptography.hazmat.backends import _get_backend
-from cryptography.hazmat.backends.interfaces import Backend, CipherBackend
 from cryptography.hazmat.primitives._cipheralgorithm import CipherAlgorithm
 from cryptography.hazmat.primitives.ciphers import modes
 
@@ -73,14 +69,8 @@ class Cipher(object):
         self,
         algorithm: CipherAlgorithm,
         mode: typing.Optional[modes.Mode],
-        backend: typing.Optional[Backend] = None,
+        backend: typing.Any = None,
     ):
-        backend = _get_backend(backend)
-        if not isinstance(backend, CipherBackend):
-            raise UnsupportedAlgorithm(
-                "Backend object does not implement CipherBackend.",
-                _Reasons.BACKEND_MISSING_INTERFACE,
-            )
 
         if not isinstance(algorithm, CipherAlgorithm):
             raise TypeError("Expected interface of CipherAlgorithm.")
@@ -90,7 +80,6 @@ class Cipher(object):
 
         self.algorithm = algorithm
         self.mode = mode
-        self._backend = backend
 
     def encryptor(self):
         if isinstance(self.mode, modes.ModeWithAuthenticationTag):
@@ -98,13 +87,17 @@ class Cipher(object):
                 raise ValueError(
                     "Authentication tag must be None when encrypting."
                 )
-        ctx = self._backend.create_symmetric_encryption_ctx(
+        from cryptography.hazmat.backends.openssl.backend import backend
+
+        ctx = backend.create_symmetric_encryption_ctx(
             self.algorithm, self.mode
         )
         return self._wrap_ctx(ctx, encrypt=True)
 
     def decryptor(self):
-        ctx = self._backend.create_symmetric_decryption_ctx(
+        from cryptography.hazmat.backends.openssl.backend import backend
+
+        ctx = backend.create_symmetric_decryption_ctx(
             self.algorithm, self.mode
         )
         return self._wrap_ctx(ctx, encrypt=False)
diff --git a/tests/hazmat/backends/test_openssl.py b/tests/hazmat/backends/test_openssl.py
index d61381d0f..5b793fc9e 100644
--- a/tests/hazmat/backends/test_openssl.py
+++ b/tests/hazmat/backends/test_openssl.py
@@ -13,7 +13,7 @@ import pytest
 
 from cryptography import utils, x509
 from cryptography.exceptions import InternalError, _Reasons
-from cryptography.hazmat.backends.openssl.backend import Backend, backend
+from cryptography.hazmat.backends.openssl.backend import backend
 from cryptography.hazmat.backends.openssl.ec import _sn_to_elliptic_curve
 from cryptography.hazmat.primitives import hashes, serialization
 from cryptography.hazmat.primitives.asymmetric import dh, dsa, padding
@@ -82,17 +82,17 @@ class TestOpenSSL(object):
             backend.register_cipher_adapter(AES, CBC, None)
 
     @pytest.mark.parametrize("mode", [DummyMode(), None])
-    def test_nonexistent_cipher(self, mode):
-        b = Backend()
-        b.register_cipher_adapter(
-            DummyCipherAlgorithm,
-            type(mode),
+    def test_nonexistent_cipher(self, mode, backend, monkeypatch):
+        # We can't use register_cipher_adapter because backend is a
+        # global singleton and we want to revert the change after the test
+        monkeypatch.setitem(
+            backend._cipher_registry,
+            (DummyCipherAlgorithm, type(mode)),
             lambda backend, cipher, mode: backend._ffi.NULL,
         )
         cipher = Cipher(
             DummyCipherAlgorithm(),
             mode,
-            backend=b,
         )
         with raises_unsupported_algorithm(_Reasons.UNSUPPORTED_CIPHER):
             cipher.encryptor()
diff --git a/tests/hazmat/primitives/test_ciphers.py b/tests/hazmat/primitives/test_ciphers.py
index bb5d0e8bd..ef577902b 100644
--- a/tests/hazmat/primitives/test_ciphers.py
+++ b/tests/hazmat/primitives/test_ciphers.py
@@ -198,17 +198,6 @@ class TestSEED(object):
             SEED("0" * 16)  # type: ignore[arg-type]
 
 
-def test_invalid_backend():
-    pretend_backend = object()
-
-    with raises_unsupported_algorithm(_Reasons.BACKEND_MISSING_INTERFACE):
-        ciphers.Cipher(
-            AES(b"AAAAAAAAAAAAAAAA"),
-            modes.ECB(),
-            pretend_backend,  # type: ignore[arg-type]
-        )
-
-
 def test_invalid_gcm_algorithm():
     with raises_unsupported_algorithm(_Reasons.UNSUPPORTED_CIPHER):
         ciphers.Cipher(