Information is an important commodity. Nations, corporations and individuals protect secret information with encryption, using a variety of methods ranging from substituting one letter for another to using a complex algorithm to encrypt a message. On the other side of the information equation are people who use a combination of logic and intuition to uncover secret information. These people are cryptanalysts, also known as code breakers.
A person who communicates through secret writing is called a cryptographer. Cryptographers might use codes, ciphers or a combination of both to keep messages safe from others. What cryptographers create, cryptanalysts attempt to unravel.
Throughout the history of cryptography, people who created codes or ciphers were often convinced their systems were unbreakable. Cryptanalysts have proven these people wrong by relying on everything from the scientific method to a lucky guess. Today, even the amazingly complex encryption schemes common in Internet transactions may have a limited useful lifetime -- quantum computing might make solving such difficult equations a snap.
To learn how code breakers crack secret messages, you need to know how people create codes. In the next section, we'll learn about some of the earliest attempts at hiding messages.