IP Puzzles +

Amidst the traffic of the Internet is an enormous amount of undesirable communication.
Currently there is no significant disincentive for clients who contribute to this
flood of undesirable communication. A mechanism for punishing only the malicious
is required in order to discourage clients from behaving badly. The standard response
has been to disconnect clients exhibiting suspicious behavior from the rest of the
network using a binary fillter. Ideally though, the mechanism should be analog to
allow falsely identified clients to prove that they are legitimate, so that service to
them can be reinstated. Client puzzles have been proposed in several protocols as a
mechanism well suited for this task;  clients do all the work involved in proving their
Reference :
Reducing Malicious Traffic With IP Puzzles
Ed Kaiser Wu-chang Feng Wu-chi Feng Antoine Luu
{edkaiser, wuchang, wuchi}@cse.ogi.edu