is it common , we increase key size to 512 Bit in AES Algorithm?

  • $\begingroup$ AES has max 256-key bits. $\endgroup$
    – kelalaka
    Nov 30, 2018 at 17:09

1 Answer 1


No. It's not even possible, never mind uncommon. If you did, it would have to be a whole new internal construction and no longer able to be called AES. Have a look at the key schedule, especially the diagram on the right hand side. 512 bits won't fit.

  • $\begingroup$ Hi , Thanks For your response.I'm studying about symmetric Encryption algorithm and I am student in Master degree.and I want to optimization one Symmetric Encryption algorithm DES or AES , please help me and sen your Idea. Best Regards. $\endgroup$
    – maryam
    Nov 30, 2018 at 18:55
  • $\begingroup$ @maryam You may have to rethink your proposal after this and the 256 bit DES question. As demonstrated, it's not possible to increase a key size beyond the specification of the common primitives. You would have to re-architect the whole thing and there are few on Earth qualified to do that securely. It would not even be optimisation, but rather ground up design. Tricky. $\endgroup$
    – Paul Uszak
    Dec 1, 2018 at 0:55
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    $\begingroup$ For a 512 bit cipher, consider working sha512 into a feistel structure. 512 bit key and 1024 bit block size. But why do this? Such a cipher would be no more secure in a practical sense, and possibly much less secure, than 128 bit AES. $\endgroup$
    – WDS
    Dec 1, 2018 at 19:05
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    $\begingroup$ You wouldn't need to change the internal construction, just run the key schedule for longer and use more rounds (for more round keys). But you're right that it would no longer be defined as AES. $\endgroup$
    – forest
    Dec 2, 2018 at 3:29
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    $\begingroup$ @PaulUszak Why wouldn't the NSA allow it? The truth is that there's simply no reason to increase the keysize. 256 bits is more than enough. It is absolutely trivial to build a cipher with an arbitrary key size from a cipher like AES. The reason people don't fork it often is because the people who understand enough about crypto to do so know that it's pointless. $\endgroup$
    – forest
    Dec 2, 2018 at 12:06

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