"""
This implementation is derived in part from the reference
Golang AES implementation, which carries the following notice:
Copyright (c) 2009 The Go Authors. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following disclaimer
in the documentation and/or other materials provided with the
distribution.
* Neither the name of Google Inc. nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""
import logging
from pprint import pprint
from aestoolbox.core.const import Sbox, powx, td0, td1, td2, td3
LOG = logging.getLogger(__name__)
[docs]class KeySchedule:
def __init__(self, key, dec=False):
self.key = key
self.dec = dec
self.xk = []
self.ixk = []
self.hkeys = {"xk": {}, "xki": {}}
self.Nk = {128: 4, 192: 6, 256: 8}
self.Nr = {128: 10, 192: 12, 256: 14}
self.validate_key()
[docs] @staticmethod
def rotw(w):
"""
Simple rotate transformation to a 4-byte word.
:param: w: 4-byte word.
:return: 4-byte transformed word.
"""
return w << 8 | w >> 24
[docs] @staticmethod
def subw(w):
"""
Apply Sbox match to each byte in word w.
:param: 4-byte word
:return: 4-byte transformed word.
"""
return (
Sbox[w >> 24 & 0xFF] << 24
| Sbox[w >> 16 & 0xFF] << 16
| Sbox[w >> 8 & 0xFF] << 8
| Sbox[w & 0xFF]
)
[docs] def validate_key(self):
k = self.key
base_len = {128, 192, 256}
if not k.startswith("0x"):
raise Exception(f'Wrong key format. Please consider this format: "0x{k}"')
return
k = k[2:]
len_k = len(k) * 4
if len_k not in {128, 192, 256}:
raise Exception(f"Wrong key size! It should be {base_len}bits instead of {len_k}")
return
if not k.strip("0123456789abcdefABCDEF") == "":
raise Exception("Wrong key format! It should be Hex.")
self.key = k
return True
[docs] def expand_key(self):
"""
Computes the expanded AES key given a 128, 192 or 256 bit key.
:return: Expanded AES Key. If `dec` is True, also returns the \n
decryption expanded AES Key in a tuple.
"""
n = 8
key = self.key
len_xk = len(key)
base = 4 * len_xk
Nk, Nr = self.Nk[base], self.Nr[base]
xkb = [0 for _ in range((Nr + 1) * 4)]
output = [key[i : i + n] for i in range(0, len_xk, n)]
for i in range(Nk):
xkb[i] = int(output[i], 16)
# Key expansion based on Golang implementation (https://golang.org/src/crypto/aes/block.go)
for i in range(Nk, (4 * (Nr + 1))):
t = xkb[i - 1]
if i % Nk == 0:
t = self.subw(self.rotw(t)) ^ (
powx[i // Nk - 1] << 24
) # It is equivalent to rcon[i//Nk-1]
elif Nk > 6 and i % Nk == 4:
t = self.subw(t)
xkb[i] = xkb[i - Nk] ^ t
# self.xk = xkb
self.hkeys["xk"] = self.format_hkeys(xkb, Nr)
if not self.dec:
return xkb
dec = [None for _ in range(len(xkb))]
# Computes the decryption expanded keys from the encryption key
for i in range(4):
dec[i] = xkb[i]
dec[((Nr + 1) - 1) * 4 + i] = xkb[((Nr + 1) - 1) * 4 + i]
for i in range(4, ((Nr + 1) - 1) * 4):
xb = xkb[i]
t = (
td0[Sbox[xb >> 24]]
^ td1[Sbox[xb >> 16 & 0xFF]]
^ td2[Sbox[xb >> 8 & 0xFF]]
^ td3[Sbox[xb & 0xFF]]
)
dec[i] = t
# self.ixk = dec
self.hkeys["xki"] = self.format_hkeys(dec, Nr)
return (dec, xkb)
[docs] def hexdump(self):
pprint(self.hkeys)