This site makes a transition from the modular arithmetic (of the last section) to writing secret codes (of this section). A Caesar cipher is a secret code in which each letter in the plain text is replaced by a letter … See the whole entry
However, as you go through the book be sure you look at all the examples in the text. If you need hints for the Level 3 … See the whole entry
Cryptography is the art of writing or deciphering messages in code. This is an applied section which uses essential ideas … See the whole entry