I am currently in the process of learning how AES actually works and that works great as of now but when it comes to the Rijndael's key schedule I have a question. From what I have read, I have to make a expanded key that is 240 bytes in size to supply enough subkeys to the whole process of a AES encryption using a 256 bit key. Does this mean that I need to make the expanded key exactly 240 bytes or can I make it 256 bytes and discard the last 16 bytes? I ask this because from what I understand, each round of the key expansion gives me 32 bytes of round keys. In that case I have to do 8 rounds of key expansion to supply the encryption with enough subkeys since 7 rounds will only give me 224 bytes.
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