You are asked when you check in if anyone has given you anything to carry for them. You presumably answered "no" to that question, yet now you're saying "Yes, they asked me to carry this unknown data".

They don't care if you know the password or not. They care if the data can be made available in plaintext or not. While you do not know the password you do know the method of making the plaintext available - you get whoever does know the passphrase to enter it. Thus, you're going to be detained until the passphrase turns up, or the machine is going to be confiscated and all data cloned and you're going to be denied entry.

Being denied entry is expensive. It also has consequences for future travel. Visas might be different. Customs clearance will be different. Possibility of getting in is lower.

> You can just tell em "Take it up with my superior back home"

They do this all the time. Watch a couple of hours of any of the various border-crossing / customs control "reality" tv shows. You'll see someone held in a room for hours, questioned for hours, with all their documents being searched for phone numbers and people being called to corroborate the story. They have no problem making phone calls back home and to the destination country.

This method is going out of your way to give them something to detain you for; it is making extra effort to look guilty.