Two Centuries On, a Cryptologist Cracks a Presidential Code - WSJ.com
http://online.wsj.com/article/SB124648494429082661.html

For more than 200 years, buried deep within Thomas Jefferson's correspondence and papers, there lay a mysterious cipher -- a coded message that appears to have remained unsolved. Until now. The cryptic message was sent to President Jefferson in December 1801 by his friend and frequent correspondent, Robert Patterson, a mathematics professor at the University of Pennsylvania. President Jefferson and Mr. Patterson were both officials at the American Philosophical Society -- a group that promoted scholarly research in the sciences and humanities -- and were enthusiasts of ciphers and other codes, regularly exchanging letters about them.

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There are three levels of game play beginner, intermediate, and advanced. As students play games, they will learn Morse Code, complete brainteasers that involve math and logic, create their own cipher machines, crack Yardleygrams and cryptograms, and learn some words in different languages.

This site from the National Security Agency offers lots of information about ciphers and codes, and lets students test their skills at detection and code-breaking.

There are three levels of game play beginner, intermediate, and advanced. As students play games, they will learn Morse Code, complete brainteasers that involve math and logic, create their own cipher machines, crack Yardleygrams and cryptograms, and learn some words in different languages.