Achievable rates for queue-based timing stegocodes

This paper studies stegocodes 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 encoding 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 algorithm is proposed to compute the maximum achievable rate of the queue-based stegocode and the optimal encoding functions.