An 802.11 MAC Layer Covert Channel
For extremely sensitive applications, it may be advantageous for users to transmit certain types of data covertly over the network. This provides an additional layer of security to that provided by the different layers of the protocol stack. In this paper, the authors present a covert side channel that uses the 802.11 MAC rate switching protocol. The covert channel provides a general method to hide communications within currently deployed 802.11 LANs. The technique uses a One-Time Password (OTP) algorithm to ensure high-entropy randomness of the covert messages. They investigate how the covert side channel affects network throughput under various rate-switching conditions with UDP-based and TCP-based application traffic.