Everyone has secrets; some have more than others. When it becomes necessary to transmit those secrets from one point to another, it's important to protect the information while it's in transit. Cryptography presents various methods for taking legible, readable data, and transforming it into unreadable data for the purpose of secure transmission, and then using a key to transform it back into readable data when it reaches its destination.
Predating computers by thousands of years, cryptography has its roots in basic transposition ciphers, which assigns each letter of the alphabet a particular value. A simple example is to assign each letter a progressively higher number, where A=1, B=2, and so forth. Using this formula for example, the word "wise GEEK", once encrypted, would read "23 9 19 5 7 5 5 11". During World War Two, machines were invented that made the ciphers more complicated and difficult to break, and today, computers have made cryptography even stronger still.
