Clues left in the clumsily encrypted notes of a Mafia don have helped Italian investigators to track his associates and ultimately contributed to his capture after years on the run. The recently busted Bernardo Provenzano, reputed to be the "boss of bosses" of the Sicilian Mafia, used a modified form of the Caesar cipher to obscure "sensitive information" in notes left to either his family or underlings.
An in-depth description of Julius Caesar's shift cipher and how it works. Also shows how to use frequency analysis and chi-square values to quickly break the cipher.
A useful document detailing the different substitution ciphers (including the Caesar Shift) and the application of Modular Arithmetic in modern day Cryptography.