What are some examples of cryptography that I might have seen?

Many young boys and girls try to create codes which they can use to communicate secret notes to each other; often, these codes will look something like this:

A	=	D
B	=	E
C	=	F

and so on. Among cryptographers, this is known as a substitution cipher, and is among the easiest of all codes to break. In fact, it is so easy that it is used as the basis of puzzles from puzzle book publishers and even appears on a daily basis in many newspapers around the United States (and, possibly, the world).

With the advent of computers, cryptography has jumped forward by leaps and bounds in many ways. It is now easier than ever to crack codes, and harder than ever to build good codes.