1 files changed, 47 insertions, 0 deletions
diff --git a/src/cryptography/hazmat/primitives/constant_time.py b/src/cryptography/hazmat/primitives/constant_time.py
new file mode 100644
index 00000000..a14eda85
--- /dev/null
+++ b/src/cryptography/hazmat/primitives/constant_time.py
@@ -0,0 +1,47 @@
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import absolute_import, division, print_function
+
+import hmac
+import os
+
+from cryptography.hazmat.bindings.utils import LazyLibrary, build_ffi
+
+
+with open(os.path.join(os.path.dirname(__file__), "src/constant_time.h")) as f:
+    TYPES = f.read()
+
+with open(os.path.join(os.path.dirname(__file__), "src/constant_time.c")) as f:
+    FUNCTIONS = f.read()
+
+
+_ffi = build_ffi(cdef_source=TYPES, verify_source=FUNCTIONS)
+_lib = LazyLibrary(_ffi)
+
+
+if hasattr(hmac, "compare_digest"):
+    def bytes_eq(a, b):
+        if not isinstance(a, bytes) or not isinstance(b, bytes):
+            raise TypeError("a and b must be bytes.")
+
+        return hmac.compare_digest(a, b)
+
+else:
+    def bytes_eq(a, b):
+        if not isinstance(a, bytes) or not isinstance(b, bytes):
+            raise TypeError("a and b must be bytes.")
+
+        return _lib.Cryptography_constant_time_bytes_eq(
+            a, len(a), b, len(b)
+        ) == 1