
Chapter 13
Random numbers and stre am ciphers
This chapter explores random numbers and random number ge nerators (RNGs).
In particular:
• The importance of random numbers for cryptog raphy.
• Tr ue RNGs.
• Pseudo RNGs.
• Cryptographically strong RNGs.
• Linear congruential RNGs.
• RNGs based on “hard” problems such as factorization.
• Stream ciphers, and their relationship with RNGs.
• Some examples of stream ciphers, including Rivest’s famous RC4.
• The Blum–Goldwasser probabilistic cryptosystem.
13.1 Introduction
Random numbers sit at the heart of almost all cryptographic and security
protocols. For example, they are needed to produce random keys for sym- ...