Initial commit

.venv/Lib/site-packages/cryptography/hazmat/primitives/kdf/hkdf.py

@@ -0,0 +1,101 @@
+# 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.
+
+from __future__ import annotations
+
+import typing
+
+from cryptography import utils
+from cryptography.exceptions import AlreadyFinalized, InvalidKey
+from cryptography.hazmat.primitives import constant_time, hashes, hmac
+from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
+
+
+class HKDF(KeyDerivationFunction):
+    def __init__(
+        self,
+        algorithm: hashes.HashAlgorithm,
+        length: int,
+        salt: bytes | None,
+        info: bytes | None,
+        backend: typing.Any = None,
+    ):
+        self._algorithm = algorithm
+
+        if salt is None:
+            salt = b"\x00" * self._algorithm.digest_size
+        else:
+            utils._check_bytes("salt", salt)
+
+        self._salt = salt
+
+        self._hkdf_expand = HKDFExpand(self._algorithm, length, info)
+
+    def _extract(self, key_material: bytes) -> bytes:
+        h = hmac.HMAC(self._salt, self._algorithm)
+        h.update(key_material)
+        return h.finalize()
+
+    def derive(self, key_material: bytes) -> bytes:
+        utils._check_byteslike("key_material", key_material)
+        return self._hkdf_expand.derive(self._extract(key_material))
+
+    def verify(self, key_material: bytes, expected_key: bytes) -> None:
+        if not constant_time.bytes_eq(self.derive(key_material), expected_key):
+            raise InvalidKey
+
+
+class HKDFExpand(KeyDerivationFunction):
+    def __init__(
+        self,
+        algorithm: hashes.HashAlgorithm,
+        length: int,
+        info: bytes | None,
+        backend: typing.Any = None,
+    ):
+        self._algorithm = algorithm
+
+        max_length = 255 * algorithm.digest_size
+
+        if length > max_length:
+            raise ValueError(
+                f"Cannot derive keys larger than {max_length} octets."
+            )
+
+        self._length = length
+
+        if info is None:
+            info = b""
+        else:
+            utils._check_bytes("info", info)
+
+        self._info = info
+
+        self._used = False
+
+    def _expand(self, key_material: bytes) -> bytes:
+        output = [b""]
+        counter = 1
+
+        while self._algorithm.digest_size * (len(output) - 1) < self._length:
+            h = hmac.HMAC(key_material, self._algorithm)
+            h.update(output[-1])
+            h.update(self._info)
+            h.update(bytes([counter]))
+            output.append(h.finalize())
+            counter += 1
+
+        return b"".join(output)[: self._length]
+
+    def derive(self, key_material: bytes) -> bytes:
+        utils._check_byteslike("key_material", key_material)
+        if self._used:
+            raise AlreadyFinalized
+
+        self._used = True
+        return self._expand(key_material)
+
+    def verify(self, key_material: bytes, expected_key: bytes) -> None:
+        if not constant_time.bytes_eq(self.derive(key_material), expected_key):
+            raise InvalidKey