Date Added: Mar 2012
Denial of Service (DoS) attacks pose a fast-growing threat to network services in the Internet, but also corporate Intranets and public local area networks like Wi-Fi hotspots may be affected. Especially protocols that perform authentication and key exchange relying on expensive public key cryptography are likely to be preferred targets. A well-known countermeasure against resource depletion attacks are client puzzles. Most existing client puzzle schemes are interactive. Upon receiving a request the server constructs a puzzle and asks the client to solve this challenge before processing its request. But the packet with the puzzle parameters sent from server to client lacks authentication. The attacker might mount a counterattack on the clients by injecting faked packets with bogus puzzle parameters bearing the server's sender address.