Chapter 10
Primes

The following two chapters explain public-key cryptographic systems. This requires some mathematics to get started. It is always tempting to dispense with the understanding and only present the formulas and equations, but we feel very strongly that this is a dangerous thing to do. To use a tool, you should understand the properties of that tool. This is easy with something like a hash function. We have an “ideal” model of a hash function, and we desire the actual hash function to behave like the ideal model. This is not so easy to do with public-key systems because there are no “ideal” models to work with. In practice, you have to deal with the mathematical properties of the public-key systems, and to do that safely you must understand these properties. There is no shortcut here; you must understand the mathematics. Fortunately, the only background knowledge required is high school math.

This chapter is about prime numbers. Prime numbers...