Julius Caesar is known to have used encrypted messages to communicate with his generals. His technique was simple by today's standards; he used letters that were three positions away in the alphabet after the intended letter. For example, the letters ABC would be represented by DEF. In fact, this encryption method is widely known as the Caeser cypher.
Another famous example of the use of cryptography, which has high historical significance, was the Enigma machine invented by the German engineer Arthur Scherbius at the end of World War I. It was commercialized in the early 1920s and the German army adopted it soon after, in order to secure its military communications. The Enigma machine has nearly 159 Quintilian different combinations of characters and numbers (more precisely 158,962,555,217,826,360,000). The Enigma cypher was considered unbreakable at the time and gave an edge to the German army during World War II. However, a team led by the brilliant English mathematician and early computer science pioneer, Alan Turing, managed to crack the Enigma code, which helped the Allies win the war. These events were recreated in the 2014 film, The Imitation Game. We'll come across further references to the genius of Alan Turing and his impact on modern computer science in Chapter 9, How Ethereum Took the Idea of Blockchain to the Next Level, where we discuss the next generation of blockchain technology—Blockchain 2.0.
Next, we'll continue learning about cryptography and we'll provide some important definitions.