I am trying to figure out AES in two rounds with 128 keys. If I have a known plaintext and the ciphertext that comes from this procedure. I get another plaintext which is similar to the previous with the difference of only one byte. I don't know the keys. Everything is 128 bits. How much will be the final ciphertext be affected?
I am taking this step by step for the two plaintexts (with one-byte difference) and I see that:
- XORing with the first key: Only the different byte will change.
- Byte substitution: Comparing the result of the 2 cases everything will stay the same except form the different byte.
- Shift byte: The two outcomes will change the same way and the different byte will still be one just in a different place.
(is that correct so far?)
- Then comes the mixcolumn... Here I am confused as to how much the result will be affected if I compare the two cases.
Any help with that?