86 lines
3 KiB
Python
86 lines
3 KiB
Python
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# This file is dual licensed under the terms of the Apache License, Version
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# 2.0, and the BSD License. See the LICENSE file in the root of this repository
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# for complete details.
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from __future__ import absolute_import, division, print_function
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import struct
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from cryptography.hazmat.primitives.ciphers import Cipher
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from cryptography.hazmat.primitives.ciphers.algorithms import AES
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from cryptography.hazmat.primitives.ciphers.modes import ECB
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from cryptography.hazmat.primitives.constant_time import bytes_eq
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def aes_key_wrap(wrapping_key, key_to_wrap, backend):
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if len(wrapping_key) not in [16, 24, 32]:
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raise ValueError("The wrapping key must be a valid AES key length")
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if len(key_to_wrap) < 16:
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raise ValueError("The key to wrap must be at least 16 bytes")
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if len(key_to_wrap) % 8 != 0:
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raise ValueError("The key to wrap must be a multiple of 8 bytes")
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# RFC 3394 Key Wrap - 2.2.1 (index method)
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encryptor = Cipher(AES(wrapping_key), ECB(), backend).encryptor()
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a = b"\xa6\xa6\xa6\xa6\xa6\xa6\xa6\xa6"
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r = [key_to_wrap[i:i + 8] for i in range(0, len(key_to_wrap), 8)]
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n = len(r)
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for j in range(6):
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for i in range(n):
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# every encryption operation is a discrete 16 byte chunk (because
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# AES has a 128-bit block size) and since we're using ECB it is
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# safe to reuse the encryptor for the entire operation
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b = encryptor.update(a + r[i])
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# pack/unpack are safe as these are always 64-bit chunks
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a = struct.pack(
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">Q", struct.unpack(">Q", b[:8])[0] ^ ((n * j) + i + 1)
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)
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r[i] = b[-8:]
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assert encryptor.finalize() == b""
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return a + b"".join(r)
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def aes_key_unwrap(wrapping_key, wrapped_key, backend):
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if len(wrapped_key) < 24:
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raise ValueError("Must be at least 24 bytes")
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if len(wrapped_key) % 8 != 0:
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raise ValueError("The wrapped key must be a multiple of 8 bytes")
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if len(wrapping_key) not in [16, 24, 32]:
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raise ValueError("The wrapping key must be a valid AES key length")
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# Implement RFC 3394 Key Unwrap - 2.2.2 (index method)
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decryptor = Cipher(AES(wrapping_key), ECB(), backend).decryptor()
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aiv = b"\xa6\xa6\xa6\xa6\xa6\xa6\xa6\xa6"
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r = [wrapped_key[i:i + 8] for i in range(0, len(wrapped_key), 8)]
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a = r.pop(0)
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n = len(r)
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for j in reversed(range(6)):
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for i in reversed(range(n)):
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# pack/unpack are safe as these are always 64-bit chunks
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atr = struct.pack(
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">Q", struct.unpack(">Q", a)[0] ^ ((n * j) + i + 1)
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) + r[i]
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# every decryption operation is a discrete 16 byte chunk so
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# it is safe to reuse the decryptor for the entire operation
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b = decryptor.update(atr)
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a = b[:8]
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r[i] = b[-8:]
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assert decryptor.finalize() == b""
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if not bytes_eq(a, aiv):
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raise InvalidUnwrap()
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return b"".join(r)
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class InvalidUnwrap(Exception):
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pass
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