Like Bitcoin, you can ask clients to find a hash of a string (in the format of, say, &#x27;server_key&#x27; + &#x27;random_number&#x27; + &#x27;client_adjusted_nonce&#x27;) with the value of the last four bytes being higher than say 50,000. You can increase the value until 0xFFFFFFFE, where only 1 in 4294967296 hashes would &#x27;pass&#x27; the test.<p>Your client will basically be working on passing the test for a predictable amount of time, dependent on the difficulty threshold.<p>The neat thing about this method is that although it takes a while to pass the test, it&#x27;s very fast and easy to check if a test is passed. You&#x27;ll simply ask the client for the client_adjusted_nonce which gets a value higher than 50,000 (or whatever difficulty threshold you choose).
As the author has stated, you can adjust the threshold depending on the strength of the DDOS.