Wireless client puzzles in IEEE 802.11 networks: security by wireless.

Resource-depletion attacks against IEEE 802,11 access points (APs) are commonly executed by flooding APs with fake authentication requests. Such attacks may exhaust an AP's memory resources and result in denied association service, thus enabling more sophisticated impersonation attacks accomplished by rogue APs. This work introduces the concept of wireless client puzzles, a protection method which assists an AP to preserve its resources by discarding fake requests, while allowing legitimate clients to successfully join the network. Rather than conditioning a puzzle's solution on computational resources of highly heterogeneous clients, the puzzles utilize peculiarities of a wireless environment such as broadcast communication and signal propagation which provide more invariant properties. Using an implementation of the proposed scheme, we demonstrate its effectiveness within a realistic scenario. Based on the insights from the implementation a simulation is used to extend the threat model and to scale up the scenario. Simulations verify our implementation results and show that the impact of flooding rate is decreased by 75% even if an attacker changes its position or manipulates its signal strength, while ≈ 90% of the legitimate stations are still able to successfully associate during an attack. Copyright 2008 ACM