A substitution cipher is a cipher which replaces individual letters (singly or in groups) with others in accordance with a definite system and a key. For example, shift the alphabet forward three places to create a new alphabet, which will be used to generate the ciphered text. This cipher was invented by Julius Caesar over two thousand years ago, and is known as the Great Caesar's cipher.

There are two types of substitution ciphers -- monoalphabetic and polyalphabetic.

A transposition cipher produces a cryptogram in which the original letters of the plain text have been rearranged according to a definite system and key. For example, spell each word of the plain text backwards to encipher it. A scytale is also an example of a simple transposition.