As a matter of logic, the results in this case (assuming the guy is honest about whether he cracks it or not) would be definitive proof that either it's crackable or that it isn't. There really isn't any leeway for "not proven" or "inconclusive" or anything like that.
(Hmmm, maybe we'd better have a couple of people try this independently, from both political parties, that way one guy can't quietly crack it and say that he didn't.)
"As a matter of logic, the results in this case (assuming the guy is honest about whether he cracks it or not) would be definitive proof that either it's crackable or that it isn't. There really isn't any leeway for "not proven" or "inconclusive" or anything like that."
It won't necessarily be conclusive. Though it might be.
If he cracks it, it's conclusive.
If he doesn't, it just means that someone with the amount of time and knowlege he had was unable to crack it in the alloted time. It doesn't mean that someone better or luckier couldn't crack it in less time, or that he couldn't have cracked it given more time.