An attack an encrypted classified data in a theoretical situation Lets say for some reason you carry AES-256-XTS encrypted data with using Whirlpool as the KDF. The data is in a 100 MB encrypted container format.

You get caught on the airport by the police. The data is so important to the country that it is the #1 priority of the intelligence service to crack it. However, no social engineering can be applied by the party that takes you in custody.

The computer on which the encryption was done has been overwritten using DoD-5220.22-M. The other party has infinite money and electricity and the best data center available.

How would they attack the file ? Would it be possible in reasonable time (less than 2 years?). If they use some kind of special attack, how would it work?
Well, given that (for whatever reason) they cannot try to overcome you with either rubber hoses or large bags of money, the next best options they would have are:


A brute force search on the password (you didn't state this, but I assume that the encrypted data is protected by a password which is the only unknown input to the KDF); if we're talking about a major TLA who is willing to throw all their resources at it, I'd expect them to be able to check all (circa) 12 character passwords (and many longer ones that don't look like line noise).
Do a black bag job on your home/work, and see if they can recover the plaintext (or a clue for the password)


Now, XTS does have weaknesses (if you update a disk block and modify only some of the 16 byte AES blocks, the attacker can see which blocks you updated); that weakness wouldn't apply here.  None of the other components are amenable to cryptanalysis.