aes-cmac: aes-cmac function using cryptolib.

python-ecosys/aes-cmac/aes_cmac.py

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

python-ecosys/aes-cmac/manifest.py

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+metadata(description="CMAC using AES from built in cryptolib library", version="0.1.0")
+module("aes_cmac.py")