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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 struct from cryptography.hazmat.backends import _get_backend from cryptography.hazmat.primitives.ciphers import Cipher from cryptography.hazmat.primitives.ciphers.algorithms import AES from cryptography.hazmat.primitives.ciphers.modes import ECB from cryptography.hazmat.primitives.constant_time import bytes_eq def _wrap_core(wrapping_key, a, r, backend): # RFC 3394 Key Wrap - 2.2.1 (index method) encryptor = Cipher(AES(wrapping_key), ECB(), backend).encryptor() n = len(r) for j in range(6): for i in range(n): # every encryption operation is a discrete 16 byte chunk (because # AES has a 128-bit block size) and since we're using ECB it is # safe to reuse the encryptor for the entire operation b = encryptor.update(a + r[i]) # pack/unpack are safe as these are always 64-bit chunks a = struct.pack( ">Q", struct.unpack(">Q", b[:8])[0] ^ ((n * j) + i + 1) ) r[i] = b[-8:] assert encryptor.finalize() == b"" return a + b"".join(r) def aes_key_wrap(wrapping_key, key_to_wrap, backend=None): backend = _get_backend(backend) if len(wrapping_key) not in [16, 24, 32]: raise ValueError("The wrapping key must be a valid AES key length") if len(key_to_wrap) < 16: raise ValueError("The key to wrap must be at least 16 bytes") if len(key_to_wrap) % 8 != 0: raise ValueError("The key to wrap must be a multiple of 8 bytes") a = b"\xa6\xa6\xa6\xa6\xa6\xa6\xa6\xa6" r = [key_to_wrap[i : i + 8] for i in range(0, len(key_to_wrap), 8)] return _wrap_core(wrapping_key, a, r, backend) def _unwrap_core(wrapping_key, a, r, backend): # Implement RFC 3394 Key Unwrap - 2.2.2 (index method) decryptor = Cipher(AES(wrapping_key), ECB(), backend).decryptor() n = len(r) for j in reversed(range(6)): for i in reversed(range(n)): # pack/unpack are safe as these are always 64-bit chunks atr = ( struct.pack( ">Q", struct.unpack(">Q", a)[0] ^ ((n * j) + i + 1) ) + r[i] ) # every decryption operation is a discrete 16 byte chunk so # it is safe to reuse the decryptor for the entire operation b = decryptor.update(atr) a = b[:8] r[i] = b[-8:] assert decryptor.finalize() == b"" return a, r def aes_key_wrap_with_padding(wrapping_key, key_to_wrap, backend=None): backend = _get_backend(backend) if len(wrapping_key) not in [16, 24, 32]: raise ValueError("The wrapping key must be a valid AES key length") aiv = b"\xA6\x59\x59\xA6" + struct.pack(">i", len(key_to_wrap)) # pad the key to wrap if necessary pad = (8 - (len(key_to_wrap) % 8)) % 8 key_to_wrap = key_to_wrap + b"\x00" * pad if len(key_to_wrap) == 8: # RFC 5649 - 4.1 - exactly 8 octets after padding encryptor = Cipher(AES(wrapping_key), ECB(), backend).encryptor() b = encryptor.update(aiv + key_to_wrap) assert encryptor.finalize() == b"" return b else: r = [key_to_wrap[i : i + 8] for i in range(0, len(key_to_wrap), 8)] return _wrap_core(wrapping_key, aiv, r, backend) def aes_key_unwrap_with_padding(wrapping_key, wrapped_key, backend=None): backend = _get_backend(backend) if len(wrapped_key) < 16: raise InvalidUnwrap("Must be at least 16 bytes") if len(wrapping_key) not in [16, 24, 32]: raise ValueError("The wrapping key must be a valid AES key length") if len(wrapped_key) == 16: # RFC 5649 - 4.2 - exactly two 64-bit blocks decryptor = Cipher(AES(wrapping_key), ECB(), backend).decryptor() b = decryptor.update(wrapped_key) assert decryptor.finalize() == b"" a = b[:8] data = b[8:] n = 1 else: r = [wrapped_key[i : i + 8] for i in range(0, len(wrapped_key), 8)] encrypted_aiv = r.pop(0) n = len(r) a, r = _unwrap_core(wrapping_key, encrypted_aiv, r, backend) data = b"".join(r) # 1) Check that MSB(32,A) = A65959A6. # 2) Check that 8*(n-1) < LSB(32,A) <= 8*n. If so, let # MLI = LSB(32,A). # 3) Let b = (8*n)-MLI, and then check that the rightmost b octets of # the output data are zero. (mli,) = struct.unpack(">I", a[4:]) b = (8 * n) - mli if ( not bytes_eq(a[:4], b"\xa6\x59\x59\xa6") or not 8 * (n - 1) < mli <= 8 * n or (b != 0 and not bytes_eq(data[-b:], b"\x00" * b)) ): raise InvalidUnwrap() if b == 0: return data else: return data[:-b] def aes_key_unwrap(wrapping_key, wrapped_key, backend=None): backend = _get_backend(backend) if len(wrapped_key) < 24: raise InvalidUnwrap("Must be at least 24 bytes") if len(wrapped_key) % 8 != 0: raise InvalidUnwrap("The wrapped key must be a multiple of 8 bytes") if len(wrapping_key) not in [16, 24, 32]: raise ValueError("The wrapping key must be a valid AES key length") aiv = b"\xa6\xa6\xa6\xa6\xa6\xa6\xa6\xa6" r = [wrapped_key[i : i + 8] for i in range(0, len(wrapped_key), 8)] a = r.pop(0) a, r = _unwrap_core(wrapping_key, a, r, backend) if not bytes_eq(a, aiv): raise InvalidUnwrap() return b"".join(r) class InvalidUnwrap(Exception): pass
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