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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 absolute_import, division, print_function

import six

from cryptography import utils
from cryptography.exceptions import (
    AlreadyFinalized, InvalidKey, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.backends.interfaces import HMACBackend
from cryptography.hazmat.primitives import constant_time, hmac
from cryptography.hazmat.primitives.kdf import KeyDerivationFunction


@utils.register_interface(KeyDerivationFunction)
class HKDF(object):
    def __init__(self, algorithm, length, salt, info, backend):
        if not isinstance(backend, HMACBackend):
            raise UnsupportedAlgorithm(
                "Backend object does not implement HMACBackend.",
                _Reasons.BACKEND_MISSING_INTERFACE
            )

        self._algorithm = algorithm

        if not (salt is None or isinstance(salt, bytes)):
            raise TypeError("salt must be bytes.")

        if salt is None:
            salt = b"\x00" * (self._algorithm.digest_size // 8)

        self._salt = salt

        self._backend = backend

        self._hkdf_expand = HKDFExpand(self._algorithm, length, info, backend)

    def _extract(self, key_material):
        h = hmac.HMAC(self._salt, self._algorithm, backend=self._backend)
        h.update(key_material)
        return h.finalize()

    def derive(self, key_material):
        if not isinstance(key_material, bytes):
            raise TypeError("key_material must be bytes.")

        return self._hkdf_expand.derive(self._extract(key_material))

    def verify(self, key_material, expected_key):
        if not constant_time.bytes_eq(self.derive(key_material), expected_key):
            raise InvalidKey


@utils.register_interface(KeyDerivationFunction)
class HKDFExpand(object):
    def __init__(self, algorithm, length, info, backend):
        if not isinstance(backend, HMACBackend):
            raise UnsupportedAlgorithm(
                "Backend object does not implement HMACBackend.",
                _Reasons.BACKEND_MISSING_INTERFACE
            )

        self._algorithm = algorithm

        self._backend = backend

        max_length = 255 * (algorithm.digest_size // 8)

        if length > max_length:
            raise ValueError(
                "Can not derive keys larger than {0} octets.".format(
                    max_length
                ))

        self._length = length

        if not (info is None or isinstance(info, bytes)):
            raise TypeError("info must be bytes.")

        if info is None:
            info = b""

        self._info = info

        self._used = False

    def _expand(self, key_material):
        output = [b""]
        counter = 1

        while self._algorithm.digest_size * (len(output) - 1) < self._length:
            h = hmac.HMAC(key_material, self._algorithm, backend=self._backend)
            h.update(output[-1])
            h.update(self._info)
            h.update(six.int2byte(counter))
            output.append(h.finalize())
            counter += 1

        return b"".join(output)[:self._length]

    def derive(self, key_material):
        if not isinstance(key_material, bytes):
            raise TypeError("key_material must be bytes.")

        if self._used:
            raise AlreadyFinalized

        self._used = True
        return self._expand(key_material)

    def verify(self, key_material, expected_key):
        if not constant_time.bytes_eq(self.derive(key_material), expected_key):
            raise InvalidKey

Filemanager

Name Type Size Permission Actions
__pycache__ Folder 0755
__init__.py File 771 B 0644
concatkdf.py File 4.01 KB 0644
hkdf.py File 3.59 KB 0644
kbkdf.py File 4.91 KB 0644
pbkdf2.py File 2.13 KB 0644
scrypt.py File 2.2 KB 0644
x963kdf.py File 2.31 KB 0644