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In this paper we propose an encoding-encryption approach to take advantage of intentional noise introduced in ciphertexts for DES based block ciphers working in CFB mode. Despite Eve's efforts in modifying her linear crytanalysis given the intercepted noisy ciphertexts, there is still a non-negligible probability of having either a crypto-analysis failure or a misdetected key under her limited resources. Consequently, we essentially create a wiretap channel in application layer that is a degraded version of the main channel, whose secrecy rate depends on the deliberately introduced bit error rate. In addition, Alice can accordingly adjust that cross over probability of the channel to maximize the 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.