Secret Key Cryptography

3 Preliminary concepts

This chapter covers

• Bits and bytes
• Functions and Boolean operators
• Prime numbers and modular arithmetic

Before we get into the meat of the subject, let’s look at some preliminary concepts. I go through these topics fairly quickly because nowadays many of these ideas are taught in schools, even in the lower grades. More of these basic ideas are given later in the book, as needed.

3.1 Bits and bytes

Data is stored in computers in the form of bits, which is shorthand for binary digits. A bit is just a number that can have the value either 0 or 1. A bit can be stored in a computer in several ways. A switch can be either open or closed. A magnet can be oriented with its north pole either up or down. Light can be polarized ...