Secrecy enhancement of block ciphered systems with deliberate noise in Non-coherent scenario

In this paper we propose an encoding-encryption approach to take advantage of intentional noise introduced in ciphertexts for a block cipher working in CFB or CBC mode. First of all, we provide a rigorous analysis of the impacts of channel degradation on block ciphered systems. We show that the overall channel can be modeled as a Finite State Markov Chain (FSMC) with symmetric channels associated in each state, whose underlying non-coherent Shannon capacity is derived and computed. Despite Eve´s efforts in modifying her linear crytanalysis given the intercepted noisy ciphertexts, there is still a non-negligible probability of having possible failures in her attack. We essentially create a wiretap channel in application layer that is a degraded version of the main channel and measure security of the system in terms of secrecy capacity and show that it depends on the deliberately introduced bit error rate. In addition, Alice can accordingly adjust cross over probability of the channel to maximize secrecy rate. This secrecy rate can be achieved by wiretap channel coding over multiple frames in application layer if the delay in system is bearable.