“…In other words, the functionalities are masked by puzzles, which need to be solved first before the prover can access the functionalities. Besides realizing various security functionalities, researchers have also applied computational puzzle schemes to mitigate a wide range of DoS attacks, such as fighting junk emails [13,12], protecting authentication protocols [2,23,29], protecting IP networks [10,14,16,20,33,34,35], protecting wireless networks [24,26], and preventing Sybil attacks [6]. With a computational puzzle scheme implemented, the server (playing the role of verifier) can mitigate an attack by asking every client (playing the role of prover) to solve a puzzle before allocating any required resource.…”