Concatenated coding and hybrid automatic repeat request for wiretap channels

In this study, the authors propose an equivocation scheme for wiretap channels, which is composed of bit‐extension mapping, coset coding and hybrid automatic repeat request (HARQ). The inner bit‐extension code and outer coset code are used for equivocation of a wiretapper channel, whereas the HARQ scheme is to mitigate noisy errors in a main legitimate channel. These concatenated codes and HARQ are effective and practical for various channel conditions. The average equivocation and the probability of causing imperfect secrecy are analysed for finite codeword lengths. As a function of channel conditions, they investigate the block error rate at the legitimate receiver and the information leakage to the wiretapper. From simulation results, they further determine the minimum requirements of code design for some target values of the ‘residual’ block error rate and information leakage at maximum retransmission.