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I was told in passing that (key, plain) pairs could be chosen to produce a zero state in AES encrypt in some middle round (say 5). [The application here being to side-channel leakage assessment.] However, I can't find any reference. I assume such a thing could be constructed from various attacks on reduced-round AES. Does anyone have a reference for the specific question (producing zero state) or for attacks that could be reverse engineered or refactored for this purpose?

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It's quite easy to find such a key, plaintext pair. All you need to do is:

  • Pick a key, any key

  • Expand the key using the standard AES key expansion process

  • Start with desired block in the middle (e.g. the all 0 block after round 5)

  • Compute the AES transform backwards (that is, in the decrypt direction) from that block

  • The final result is the plaintext block.

I don't expect you'd be able to find a reference to this procedure - it's too obvious to be considered publishable...

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    $\begingroup$ OK, guess I was overthinking it. The person who said this made it seem like they knew some magic trick. $\endgroup$
    – yoyo
    Dec 7, 2023 at 20:02

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