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dist/ba_data/python-site-packages/cryptography/hazmat/primitives/kdf/x963kdf.py

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+# 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
+from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
+
+
+def _int_to_u32be(n: int) -> bytes:
+    return n.to_bytes(length=4, byteorder="big")
+
+
+class X963KDF(KeyDerivationFunction):
+    def __init__(
+        self,
+        algorithm: hashes.HashAlgorithm,
+        length: int,
+        sharedinfo: typing.Optional[bytes],
+        backend: typing.Any = None,
+    ):
+        max_len = algorithm.digest_size * (2**32 - 1)
+        if length > max_len:
+            raise ValueError(f"Cannot derive keys larger than {max_len} bits.")
+        if sharedinfo is not None:
+            utils._check_bytes("sharedinfo", sharedinfo)
+
+        self._algorithm = algorithm
+        self._length = length
+        self._sharedinfo = sharedinfo
+        self._used = False
+
+    def derive(self, key_material: bytes) -> bytes:
+        if self._used:
+            raise AlreadyFinalized
+        self._used = True
+        utils._check_byteslike("key_material", key_material)
+        output = [b""]
+        outlen = 0
+        counter = 1
+
+        while self._length > outlen:
+            h = hashes.Hash(self._algorithm)
+            h.update(key_material)
+            h.update(_int_to_u32be(counter))
+            if self._sharedinfo is not None:
+                h.update(self._sharedinfo)
+            output.append(h.finalize())
+            outlen += len(output[-1])
+            counter += 1
+
+        return b"".join(output)[: self._length]
+
+    def verify(self, key_material: bytes, expected_key: bytes) -> None:
+        if not constant_time.bytes_eq(self.derive(key_material), expected_key):
+            raise InvalidKey