I saw the AES algorithm that at the end of algorithm the buffer that stored in the beginning of algorithm the encrypt/decrypt key. now is store the last subkey.
What is the last subkey? Why do I need to know it?
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In AES, a certain amount of rounds of encryption are performed. The amount of rounds depends on the length of the key (128/192/256 bits). The key is expanded through the
key schedule function, and at each round, the sub key is the next 16 bytes of the expanded key. Each round, the sub key is XORed against the current state. So the sub key has to be known in order to perform the encryption.