just slight update

week05/easy/no_test.py

@@ -0,0 +1,79 @@
+import random
+import binascii
+from Crypto.Cipher import AES
+from Crypto.Hash import CMAC, HMAC, SHA256
+import hashlib
+
+KEY = b'1337133713371337'
+
+
+def pkcs7(message: bytes, block_size: int = 16) -> bytes:
+    gap_size = block_size - (len(message) % block_size)
+    return message + bytes([gap_size] * gap_size)
+
+
+def calc_cbc_mac(message: bytes, iv: bytes, key: bytes) -> bytes:
+    cipher = AES.new(key, AES.MODE_CBC, iv)
+    message = pkcs7(message)
+    last_block = cipher.encrypt(message)[-16:]
+    return last_block
+
+def calc_hmac(message: bytes, key: bytes) -> bytes:
+    # Create HMAC object with the key and message using SHA-256
+    hmac = HMAC.new(KEY, msg=message, digestmod=SHA256)
+
+    # Calculate the HMAC
+    mac = hmac.hexdigest()
+    return mac
+
+
+
+def calc_cmac(message: bytes, key: bytes) -> bytes:
+    c = CMAC.new(key, ciphermod=AES)
+    c.update(message)
+    return c.digest()
+
+
+def calc_pure_cmac(message: bytes, key: bytes) -> bytes:
+    def left_shift(k):
+        """Perform left shift on a byte string with overflow handling"""
+        result = bytearray(k)
+        overflow = result[0] & 0x80
+        for i in range(len(result)):
+            result[i] <<= 1
+            if i > 0:
+                result[i] |= (1 if result[i-1] & 0x80 else 0)
+    
+        if overflow:
+            result[-1] ^= 0x87
+    
+         return bytes(result)
+
+
+    def xor_bytes(a, b):
+        """XOR two byte strings"""
+        return bytes(x ^ y for x, y in zip(a, b))
+
+
+
+
+
+def check_challenge(challenge: bytes):
+    return (
+        calc_cbc_mac(challenge, b'\x00' * 16, KEY),
+        calc_cmac(challenge, KEY),
+        calc_hmac(challenge, KEY)
+    )
+
+def decode_message(msg):
+    return binascii.unhexlify(msg)
+
+
+def main():
+    challenge = "f681e8625406c40419ae7771eac8f8a2eb6a6fcb1fc0396ab8fdca793a27c93a6dafbb"
+    challenge = decode_message(challenge)
+    print(check_challenge(challenge))
+
+
+if __name__ == "__main__":
+    main()