Making a Paper Cipher Wheel

Before we learn how to program computers to do encryption and decryption for us, let’s learn how to do it ourselves with simple paper tools. It is easy to turn the understandable English text (which is called the plaintext) into the gibberish text that hides a secret code (called the ciphertext). A cipher is a set of rules for converting between plaintext and ciphertext. These rules often use a secret key. We will learn several different ciphers in this book.
Let’s learn a cipher called the Caesar cipher. This cipher was used by Julius Caesar two thousand years ago. The good news is that it is simple and easy to learn. The bad news is that because it is so simple, it is also easy for a cryptanalyst to break it. But we can use it as a simple learning exercise. To convert plaintext to ciphertext using the Caesar cipher, we will create something called a cipher wheel (also called a cipher disk). You can either photocopy the cipher wheel that appears in this book,  Cut out the two circles and lay them on top of each other like in Figure




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