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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.
import sys
from cryptography import utils
from cryptography.exceptions import (
AlreadyFinalized,
InvalidKey,
UnsupportedAlgorithm,
_Reasons,
)
from cryptography.hazmat.backends import _get_backend
from cryptography.hazmat.backends.interfaces import ScryptBackend
from cryptography.hazmat.primitives import constant_time
from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
# This is used by the scrypt tests to skip tests that require more memory
# than the MEM_LIMIT
_MEM_LIMIT = sys.maxsize // 2
class Scrypt(KeyDerivationFunction):
def __init__(
self, salt: bytes, length: int, n: int, r: int, p: int, backend=None
):
backend = _get_backend(backend)
if not isinstance(backend, ScryptBackend):
raise UnsupportedAlgorithm(
"Backend object does not implement ScryptBackend.",
_Reasons.BACKEND_MISSING_INTERFACE,
)
self._length = length
utils._check_bytes("salt", salt)
if n < 2 or (n & (n - 1)) != 0:
raise ValueError("n must be greater than 1 and be a power of 2.")
if r < 1:
raise ValueError("r must be greater than or equal to 1.")
if p < 1:
raise ValueError("p must be greater than or equal to 1.")
self._used = False
self._salt = salt
self._n = n
self._r = r
self._p = p
self._backend = backend
def derive(self, key_material: bytes) -> bytes:
if self._used:
raise AlreadyFinalized("Scrypt instances can only be used once.")
self._used = True
utils._check_byteslike("key_material", key_material)
return self._backend.derive_scrypt(
key_material, self._salt, self._length, self._n, self._r, self._p
)
def verify(self, key_material: bytes, expected_key: bytes) -> None:
derived_key = self.derive(key_material)
if not constant_time.bytes_eq(derived_key, expected_key):
raise InvalidKey("Keys do not match.")
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