Human ingenuity cannot concoct a cypher which human ingenuity cannot resolve.
-- Edgar Allen Poe
Descriptions of Historical Ciphers
Overview
Caesar Cipher
Simple Substitution Cipher
Vigenere Cipher
Gronsfeld Cipher
The German Enigma Machine
RSA Public Key Encryption
PGP -- Pretty Good Protection
Rail Fence Cipher
Alberti Cipher
Edgar Allen Poe