Other Stream Ciphers and Real Random‐Sequence Generators
Bruce Schneier · 2015
This chapter explains a list of stream ciphers and real random-sequence generators. The discussed stream ciphers include RC4, SEAL, word auto key encryption (WAKE) algorithm, and feedback with carry shift register (FCSR) stream ciphers. In practice, stream-cipher design is a lot like block-cipher design. It involves more mathematical theory, but in the end a cryptographer proposes a design and then tries to analyze it. According to Rainer Rueppel, there are four different approaches to the construction of stream ciphers: system-theoretic approach, information-theoretic approach, complexity-theoretic approach, and randomized approach. A cryptographer attempts to use complexity theory to prove that his generators are secure. The simplest and most efficient complexity-theoretic generator is called the Blum, Blum, and Shub generator, after its inventors. In general, the best way to generate random numbers is to find a whole lot of seemingly random events and distill randomness from them.