Modes of operation of stream ciphers

Abstract

A general stream cipher with memory in which each ciphertext symbol depends on both the current and previous plaintext symbols, as well as each plaintext symbol depends on both the current and previous ciphertext symbols, is pointed out. It is shown how to convert any keystream generator into a stream cipher with memory and their security is discussed. It is proposed how to construct secure self-synchronizing stream ciphers, keyed hash functions, hash functions, and block ciphers from any secure stream cipher with memory. Rather new and unusual designs can thus be obtained, such as the designs of block ciphers and (keyed) hash functions based on clock-controlled shift registers only.