What is Cryptography?

Cryptography is the study of encoding and decoding secret messages.

Caesar Shift Code

Julius Caesar used a substition shift code to send messages to his army more than 2,000 years ago. In the Caesar Shift Code, a letter is replaced by another letter a fixed number of positions down in the alphabet. For example, "CAT" becomes "FDW" using a shift key of 3.
CAT → (shift 3) FDW

Cracking Substitution Codes