Tradeoff between reliability and security in block ciphering systems with physical channel errors

In this paper, we study the effects of channel errors on security and decoding error probability of three encryption systems where encrypted message is sent and eavesdropped over binary symmetric channels (BSC). The three systems are all based on Data Encryption Standard (DES) in cipher feedback (CFB) mode. They are DES only (DC), DES concatenated with Reed Solomon encoding (DCRS), and DES concatenated with RS coding and S-box diffusion (DCRSS). We adopt linear crypt-analysis to quantitatively measure the effects of channel errors on the security of these systems. We have found the required known cipher-plain text pairs in each system for linear attack launched by Eve, an eavesdropper. In addition, performance analysis in terms of decoded information bit error probability (IBER) for Bob, the legitimate receiver, has been conducted for each system, whose accuracy is later verified by simulation results. Our results suggest there exists tradeoff between communication reliability and security. More security level can be attained by sacrificing the accuracy at the legitimate receiver end, which can be captured by the relationship between IBER and our proposed novel metric, security improvement factor (SIF).