The CodeHelp page, a program to aid in the decryption (and encryption) of messages using "paper-and-pencil" methods found in the book Elementary Cryptanalysis by Abraham Sinkov, published by the MAA.
Here is an origami folding pattern for a Denison Block D that you can make with one straight cut.
I have Pringle can Enigma cutouts, with instructions. When assembled, the device simulates the German Enigma encryption machine from World War Two. This idea seems to originate with the people doing the National Cipher Challenge in the UK, but the templates are no longer available. I made up my own here.
You can download errata (a pdf file) for A First Course in Abstract Algebra: Rings, Groups, and Fields, 2nd edition, published by Chapman & Hall/CRC Press, 2005,
by Anderson and Feil. (Last update: 15 December, 2008.)
See a brief review from the MAA.
You can download errata (a pdf file) for Essential Discrete Mathematics for Computer Science (Prentice-Hall)
by Feil and Krone. (Last update: 15 December 2008.)
