Simon Singh's "Code Book" and the Cipher Challenge
Just finished reading Simon Singh's "Code Book", which I find a very entertaining read on the history of cryptography. He has some very entertaining details on the earlier history, inl. how weak encryption killed Mary Stuart. At the end of the book is a cipher challenge, that actually took on an interesting life of it's own. (Simon Singh has a really nice website.)
Actually, the story of how the Swedes solved the Cipher Challenge deserves a direct link "How we cracked the code book ciphers". (Great reading!)  ¶ permanent link