Stop explicitly enabling RSA blinding

It is on by default in OpenSSL, going back at least as far 1.1.1d, and probably much farther.

src/cryptography/hazmat/backends/openssl/rsa.py

@@ -4,7 +4,6 @@
 
 from __future__ import annotations
 
-import threading
 import typing
 
 from cryptography.exceptions import (
@@ -400,9 +399,6 @@ def __init__(
         self._backend = backend
         self._rsa_cdata = rsa_cdata
         self._evp_pkey = evp_pkey
-        # Used for lazy blinding
-        self._blinded = False
-        self._blinding_lock = threading.Lock()
 
         n = self._backend._ffi.new("BIGNUM **")
         self._backend._lib.RSA_get0_key(
@@ -414,31 +410,11 @@ def __init__(
         self._backend.openssl_assert(n[0] != self._backend._ffi.NULL)
         self._key_size = self._backend._lib.BN_num_bits(n[0])
 
-    def _enable_blinding(self) -> None:
-        # If you call blind on an already blinded RSA key OpenSSL will turn
-        # it off and back on, which is a performance hit we want to avoid.
-        if not self._blinded:
-            with self._blinding_lock:
-                self._non_threadsafe_enable_blinding()
-
-    def _non_threadsafe_enable_blinding(self) -> None:
-        # This is only a separate function to allow for testing to cover both
-        # branches. It should never be invoked except through _enable_blinding.
-        # Check if it's not True again in case another thread raced past the
-        # first non-locked check.
-        if not self._blinded:
-            res = self._backend._lib.RSA_blinding_on(
-                self._rsa_cdata, self._backend._ffi.NULL
-            )
-            self._backend.openssl_assert(res == 1)
-            self._blinded = True
-
     @property
     def key_size(self) -> int:
         return self._key_size
 
     def decrypt(self, ciphertext: bytes, padding: AsymmetricPadding) -> bytes:
-        self._enable_blinding()
         key_size_bytes = (self.key_size + 7) // 8
         if key_size_bytes != len(ciphertext):
             raise ValueError("Ciphertext length must be equal to key size.")
@@ -508,7 +484,6 @@ def sign(
         padding: AsymmetricPadding,
         algorithm: typing.Union[asym_utils.Prehashed, hashes.HashAlgorithm],
     ) -> bytes:
-        self._enable_blinding()
         data, algorithm = _calculate_digest_and_algorithm(data, algorithm)
         return _rsa_sig_sign(self._backend, padding, algorithm, self, data)
 

tests/hazmat/primitives/test_rsa.py

@@ -451,45 +451,6 @@ def test_oaep_wrong_label(self, rsa_key_2048, enclabel, declabel, backend):
                 ),
             )
 
-    @pytest.mark.supported(
-        only_if=lambda backend: backend.rsa_encryption_supported(
-            padding.PKCS1v15()
-        ),
-        skip_message="Does not support PKCS1v1.5.",
-    )
-    def test_lazy_blinding(self, backend):
-        # We don't want to reuse the rsa_key_2048 fixture here because lazy
-        # blinding mutates the object to add the blinding factor on
-        # the first call to decrypt/sign. Since we reuse rsa_key_2048 in
-        # many tests we can't properly test blinding, which will (likely)
-        # already be set on the fixture.
-        private_key = RSA_KEY_2048.private_key(
-            unsafe_skip_rsa_key_validation=True
-        )
-        public_key = private_key.public_key()
-        msg = b"encrypt me!"
-        ct = public_key.encrypt(
-            msg,
-            padding.PKCS1v15(),
-        )
-        assert private_key._blinded is False  # type: ignore[attr-defined]
-        pt = private_key.decrypt(
-            ct,
-            padding.PKCS1v15(),
-        )
-        assert private_key._blinded is True  # type: ignore[attr-defined]
-        # Call a second time to cover the branch where blinding
-        # has already occurred and we don't want to do it again.
-        pt2 = private_key.decrypt(
-            ct,
-            padding.PKCS1v15(),
-        )
-        assert pt == pt2
-        assert private_key._blinded is True
-        # Private method call to cover the racy branch within the lock
-        private_key._non_threadsafe_enable_blinding()
-        assert private_key._blinded is True
-
 
 class TestRSASignature:
     @pytest.mark.supported(