4 ms·
I'd tell my friend to feel for the warm coin, and I'd hold the coin I'm intended to flip as long and as tightly as possible before flipping it.
by spdustin 12y ago
I'd tell my friend to feel for the warm coin, and I'd hold the coin I'm intended to flip as long and as tightly as possible before flipping it.
- JonathonW 12y agoOne of the constraints of the problem is that your friend can't touch the board, so, unless he has IR vision, that could be problematic.
- spdustin 12y agoDoesn't have to touch the board. Just the coins. It's semantic distinction, sure, but if the jailer is capricious enough to envision this challenge, he should be impressed by a solution's cleverness.
- TrainedMonkey 12y agoJailer notices that and waits for an hour before letting your friend in, all coins are room temperature by that point.
- Spl3en 12y agoAnother side effect generated from the experience : There is no time limit for flipping the first coin, so if the guard choses the first square, I would wait 1 min before flipping mine. 60th square ? I would wait an hour. If my friend outside is able to know precisely when I enter / exit from the room, he is able to know the correct square.
- sarciszewski 12y agoHeh. Timing side-channel for the win. :D