@ingox That's it!
Now, suppose that instead of the current spam protection on this forum, the admin did the following:
- When a person wants to make a post, the forum sends a randomly chosen 16-beat pattern to the poster and requires the poster to send back the correct seed with their post
- The poster uses your brute-force method to compute the correct seed and sends it back with their post
- The forum software checks whether the seed actually computes the correct beat pattern. If it does then it lets the post through. If not, it blocks it.
Step 3 is easy-- just set the user's seed, send 16 bangs to [random 2] and check if the output matches.
Step 2 is hard-- in your case it took 4481 times through the loop to get the right answer.
Step 1 is easy-- most OSes have a way to spit out an unpredictable sequence of bits
Furthermore, if we add steps to the sequencer the job gets harder for the poster to find the seed, but it stays (relatively) easy for the forum website to verify the correct answer. That means the website can try different size sequencers to reach a nice balance between spam-prevention and user frustration.
Congratulations-- we've just re-invented hash cash, the key ingredient behind Bitcoin payment validations.
