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?
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...