For one of the best written books on the history of computers, check out Engines of the Mind : The Evolution of  the Computer from Mainframes to Microprocessors -- by Joel N. Shurkin (Paperback)

A movingly beautiful book on Alan Turing is Alan Turing: the Enigma, by Andrew Hodges

An excellent, readable book on Cryptography is Simon Singh’s THE CODE BOOK.  The Secret History of Codes and Code-Breaking

Tutorials on the encryption software PGP (Pretty Good Privacy) can be found at   http://www.pitt.edu/~poole/PGPintro.htm

All pictures and some of the information were obtained from various sites on the World Wide Web.  Complete list follows:

Abacus: http://qi-journal.com/action.lasso?-Token.SearchID=Abacus&-Response=culture.asp

Napier: http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Napier.html

  http://www.maxmon.com/1600ad.htm

Slide Rules: http://www.hpmuseum.org/sliderul.htm

Pascal’s Pascaline: http://www.thocp.net/hardware/pascaline.htm

Leibnitz Stepped Reckoner: http://en.wikipedia.org/wiki/Stepped_Reckoner

Jacquard looms: http://history.acusd.edu/gen/recording/jacquard1.html

  http://www.deutsches-museum.de/ausstell/meister/e_web.htm