Achievable rates for queue-based timing stegocodes

This work studies stegocodes (data-hiding codes) for covert communication over timing channels. In a timing channel, the information resides in the packet interdeparture times as opposed to the packets themselves. The en- coding procedure should preserve the statistics of the packet interarrival process. Our steganographic codes are based on two novel ideas, namely, queue- based codes and Shannon's encoding functions for channels with causal side information at the transmitter. The embedding of information bits is done by a Geo/Geo/1 queue servicing the interarrival times. Shannon's theory of coding with causal side information at the transmitter is then used to study the queue-based stegocodes and their information-theoretic limits. Evaluating these limits for the Geo/Geo/1 queue is a formidable computational problem. An efficient computational approach is proposed to compute the maximum achievable rate of the queue-based stegocode and the optimal encoding functions. We also design simple practical codes, test them on a communication system while taking network noise into account, and compare their performance to the mappings under study