While the puzzle creator may intend for the funds to be claimed by cracking the key, that doesn’t automatically make it legal. Most jurisdictions don’t recognize brute-forcing as a valid way to transfer ownership. It’s still technically unauthorized access under computer crime laws. The creator’s forum posts might show intent, but unless they structured this as a binding contract or explicit waiver, the law could still view solvers as committing theft. In practice, nobody gets prosecuted because  is pseudonymous and the creator isn’t complaining, but that doesn’t make it legally safe.