Trying to make sense of the various applications of crypto, I came up with an illustration of their 'dependancies' at http://rattler.otc.net/crypto/mydocs/taxonomy.gif This picture illustrates topics that you should learn before others. For instance, digital watermarking depends on steganography and message-authentication codes. Anonymity requires understanding traffic mixing and practical encryption; practical encryption requires understanding public and secret key encryption. FWIW. Comments welcome. ------------------------------------------------------------ David Honig Orbit Technology honig@otc.net Intaanetto Jigyoubu "How do you know you are not being deceived?" ---A Compendium of Analytic TradeCraft Notes, Directorate of Intelligence, CIA http://www.jya.com/cia-notes.htm