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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

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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.

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    $\begingroup$ You can interpret the initial XOR by the truncated original key to be a 15th round key. $\endgroup$
    – Myria
    Commented Jun 15, 2023 at 20:43

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