Some weeks ago, I rented the 2007 adventure film National Treasure: Book of Secrets on DVD, in which treasure hunter Benjamin Franklin Gates (played by Nicholas Cage) looks to discover the truth behind the assassination of Abraham Lincoln. In the movie’s first scene, which takes place in a tavern in Washington, D.C. five days after the end of the Civil War, Ben Gates’ great-great-grandfather Thomas Gates is approached by John Wilkes Booth and another member of the Knights of the Golden Circle, who ask him to decipher a secret message, which has obviously been encrypted using the Playfair cipher and might lead them to a mythological city of gold called Cíbola.

As the Playfair cipher was state-of-the-art at the end of the Civil War in 1865, I wondered how someone (even if portrayed as a well-known puzzle solver) would be able to perform a successful ciphertext-only attack within just one or two hours, not having any frequency tables at hand and given a ciphertext consisting of only 22 digraphs (= pairs of letters). The following article will explain the basic concepts (encryption, decryption and cryptanalysis) of the Playfair cipher using the example from National Treasure: Book of Secrets.

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Sorry that there have been only two posts since the start of this blog on 8th August. I have neither lost interest only days after kickoff nor have I been kidnapped by some dark intelligence agency. On the contrary, I have been spending a lot of time on fixing numerous visible and invisible bugs, especially in the translated versions of this blog. Moreover, there is a whole bunch of new features available like a highly scalable FAQ and LaTeX support for posts and comments!

I am optimistic that the stage of initial installations and bug fixes has come to an end now, so that from this point on, I can exclusively focus on what this blog is really about: cryptology! On my desk, there are already some drafts about the Playfair cipher, which was extensively referred to in the blockbuster “National Treasure: Book of Secrets” (2007), and the Japanese code JN-25, which played a decisive role in WWII’s Battle for the Pacific. So please stay tuned for what’s to come in the near future!