Trade-Off Between Security and Performance in Block Ciphered Systems With Erroneous Ciphertexts

It has long been held that errors in received noisy ciphertexts should be eliminated using as many as possible powerful error correcting codes in order to reduce the avalanche effect on legitimate users´ performance in block ciphered systems. However, the negative effect of erroneous ciphertexts on cryptanalysis by an eavesdropper has not been well understood, nor the possible measurable trade-off between security enhancement and performance degradation under noisy ciphertexts. To address these questions, we have launched a case study in this paper using Data Encryption Standard (DES)-based block ciphers operating in cipher feedback (CFB) mode to show quantitatively the pros and cons of exploiting voluntarily or nonvoluntarily introduced binary errors in ciphertexts of block ciphered systems using our proposed comparison metrics. A serially concatenated scheme with both outer and inner encoder-encipher pairs is proposed which allows us to quantitatively reveal the sacrifice made by legitimate users in its postdecryption capacity, as well as the security improvement factor (SIF) which reflects the additionally required plaintext-ciphertext pairs for eavesdropper´s known plaintext attack, in the presence of noise in ciphertexts. Simulation results demonstrate the accuracy of derived approximations of the postdecryption performance for the legitimate receiver.