What is Cryptography?
Look at the following two pieces of text:
The text on the left side is a secret message. The message has been encrypted, or turned into a secret code. It will be completely unreadable to anyone who doesn’t know how to decrypt it (that is, turn it back into the plain English message.) This book will teach you how to encrypt and
The message on the right is just random gibberish with no hidden meaning whatsoever. Encrypting your written messages is one way to keep them secret from other people, even if they get their hands on the encrypted message itself. It will look exactly like random nonsense. Cryptography is the science of using secret codes. A cryptographer is someone who uses and studies secret codes. This book will teach you what you need to know to become a cryptographer.
Of course, these secret messages don’t always stay secret. A cryptanalyst is someone who can hack secret codes and read other people’s encrypted messages. Cryptanalysts are also called code breakers or hackers. This book will also teach you what you need to know to become a cryptanalyst. Unfortunately the type of hacking you learn in this book isn’t dangerous enough to get you in trouble with the law. (I mean, fortunately.)
Spies, soldiers, hackers, pirates, royalty, merchants, tyrants, political activists, Internet shoppers, and anyone who has ever needed to share secrets with trusted friends have relied on cryptography to make sure their secrets stay secret.