The ironic part in Bitcoin is that it's a completely artificial (albeit carefully planned) market that aims to create the ultimate free market, why haven't the devs put any effort into a bounty system to tap into bitcoins network hashing potential? Call it Bitcoin+ and let people put up bounties for unique addresses/darknet union URLs, cracking FBI/bank passwords etc.
One important reason for having the seemingly pointless proof of work problem that bitcoin uses (as opposed to a useful problem), is that its difficulty can be adjusted up and down to regulate the block discovery time. If you were solving a useful problem like cracking keys, how could the difficulty be adjusted?