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Three different versions of the Advanced Encryption Standard (AES) have been standardized, which use keys of bit length 128, 192, and 256 respectively. They also use different numbers of rounds: 10, 12, and 14 rounds respectively. But my understanding is that the three versions of AES are otherwise extremely similar.

  1. How much additional information would need to be specified in order to create a new version of AES with a different key length? Do the key length and the number of rounds pretty much nail down the whole algorithm in sufficient detail that you can just say "Okay, my new version of AES has key length 64 bits and you use 8 rounds", and it's obvious how to fill in the rest of the details? Or do you need to do a lot more work? (I know that Rijndael also allows key sizes 160 and 224 bits, but I'm wondering about going beyond those bounds.)
  2. Would such a new version of AES require extensive new cryptanalysis, or would it just be a simple matter of plugging the new bit length and number of rounds into already-known formulas in order to estimate the hardness of decryption?

I know that there are more version-specific details beyond just the bit length and the number of rounds, such as the key schedule, but I'm not familiar with what those details are.

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    $\begingroup$ NIST was initially asked for 128,160,192,224, and 256-bit key and block size, later they changed what we have in AES since there is no need!. They are very similar since they have the size of the same block. The answer to your question is opinion-based. Rijndael is not immediately designed, the first designed SHARK, then Square then BKSQ. It is years of reading understanding and experience.You can see from the book T_he Design of Rijndael The Advanced Encryption Standard (AES) Second Edition_ $\endgroup$
    – kelalaka
    Jan 1, 2022 at 20:20
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    $\begingroup$ Read the The Design of Rijndael The Advanced Encryption Standard (AES) Second Edition There you can find clues... $\endgroup$
    – kelalaka
    Jan 1, 2022 at 21:22
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    $\begingroup$ Just to increase the key size the round goes 10, 12, 14 doesn't mean that 512 will have 19 rounds. They have analyzed it and the time showed that one should have 15 instead of 14. $\endgroup$
    – kelalaka
    Jan 1, 2022 at 21:26
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    $\begingroup$ To be honest I think that what you are asking for is too generic. It depends on the change that you make how much of the crypt-analysis needs to be changed, if at all. Adding key sizes doesn't make much sense as AES-128 is secure against any attacks with normal computers. To protect against multi-target and quantum computers you can use AES-256. Any other attacks depend on other, unknown attack vectors. With the advantage of hindsight, I think that AES-192 was already a mistake. $\endgroup$
    – Maarten Bodewes
    Jan 2, 2022 at 19:18
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