A PLL Based Approach to Building an Effective Covert Timing Channel

Covert channel is used to secretly transfer information. In covert timing channels, all messages are decoded based on the arrival time of packets at the receiver side. In covert communications, synchronization between the sender and receiver plays a key role in decoding accuracy. Lost, duplicated, and out-of-order arrived packets may cause the loss of synchronization between the sender and receiver. In this study, a synchronization scheme, which is based on Phase Lock Loop (PLL), is proposed to build an effective covert timing channel. The scheme is software based and implemented in the transport layer. This is the first effort of using PLL for building a covert channel. Simulation results show that the scheme can achieve high decoding rate. Moreover, the covert timing channel built by the scheme is not affected by packet loss, duplication, and out-of-order arrival.