Optimal stream-based cipher feedback mode in error channel

Abstract

Block ciphers encrypt a fixed size block of plaintext at a time to produce a block of ciphertext. Stream ciphers encrypt stream data, such as voice or Telnet traffic, one bit or more bits at a time. The cipher feedback mode is one stream cipher implemented by a block cipher via multiple stages, and in each stage, one bit or a number of bits of plaintext are encrypted at a time. In this paper, we study error performance of the stream-based cipher feedback mode in an error channel in terms of throughput. We model performance of the cipher feedback mode in terms of the probability that part/whole of the ciphertext cannot be successfully decrypted, as well as the throughput by adopting the cipher feedback mode. We explicitly derive the optimal number of stages in the cipher feedback mode to achieve the optimal throughput, given an error rate.