kopia lustrzana https://github.com/micropython/micropython-lib
75 wiersze
1.9 KiB
Python
75 wiersze
1.9 KiB
Python
#!/usr/bin/python3
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import cryptolib
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from binascii import hexlify
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from math import ceil
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class CMAC:
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def _xor(self, a, b):
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return bytes(x ^ y for x, y in zip(a, b))
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def _e(self, key, plain):
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aes = cryptolib.aes(key, 1) # Using ECB mode
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return aes.encrypt(plain)
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def _d(self, key, enc):
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aes = cryptolib.aes(key, 1) # Using ECB mode
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return aes.decrypt(enc)
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def generate_subkey(self, k):
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const_zero = b"\x00" * 16
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const_rb = b"\x87" + b"\x00" * 15 # Adjusted to align with common CMAC practices
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# Step 1
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l = self._e(k, const_zero)
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# Step 2 and 3
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def shift_left(bit_string):
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shifted = int.from_bytes(bit_string, "big") << 1
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if bit_string[0] & 0x80:
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shifted ^= 0x100000000000000000000000000000087 # Apply Rb polynomial
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return shifted.to_bytes(16, "big")
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k1 = shift_left(l)
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k2 = shift_left(k1)
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return k1, k2
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def aes_cmac(self, k, m):
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const_zero = b"\x00" * 16
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const_bsize = 16
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# Step 1
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k1, k2 = self.generate_subkey(k)
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# Step 2
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n = ceil(len(m) / const_bsize)
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m_block = [m[i * const_bsize : (i + 1) * const_bsize] for i in range(n)]
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# Step 3
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if n == 0:
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n = 1
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m_block = [b""]
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flag = False
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else:
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flag = len(m) % const_bsize == 0
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# Step 4
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if flag:
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m_last = self._xor(m_block[-1], k1)
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else:
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padding = b"\x80" + b"\x00" * (const_bsize - len(m_block[-1]) - 1)
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m_last = self._xor(m_block[-1] + padding, k2)
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# Step 5 and 6
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x = const_zero
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for block in m_block[:-1]:
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y = self._xor(x, block)
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x = self._e(k, y)
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y = self._xor(m_last, x)
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t = self._e(k, y)
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# Step 7
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return t
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