Score:0

How to find the round key in AES 256

tf flag

Can anyone explaine how to find the every 15 round key by the 64 hex digit master key of AES 256 please. I will be really greatfull

Score:2
sa flag

This is easily found online but there seems to be no specific question asked on the AES key schedule itself, so I am answering. There are questions about the strength of the generated round keys and so on.

The function deriving the round keys from the master key is called the AES Key Schedule: https://en.wikipedia.org/wiki/AES_key_schedule It uses a linear recurrence, rotations as well as the nonlinear Sbox function of AES.

As you can see from https://en.wikipedia.org/wiki/Advanced_Encryption_Standard you actually derive 10 or 12 or 14 round keys from the master key which is (128 or 192 or 256 bits long respectively), so I don't know where you are getting your 15 round keys from.

Myria avatar
in flag
You can interpret the initial XOR by the truncated original key to be a 15th round key.
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