A useful document detailing the different substitution ciphers (including the Caesar Shift) and the application of Modular Arithmetic in modern day Cryptography.
This article gives a method for generating secure yet easy to remember passwords for online accounts, using encryption and modular arithmetic (!). It is an interesting use of encryption in everyday life for something we all have, password-protected internet accounts. If you click through to the computer science category, you can find other posts on cryptography, encryption, and privacy.