According to Garfinkel and Spafford’s Practical UNIX and Internet Security , cryptography was used as a tactical measure as early as ancient Greece. Spartan generals exchanged secret messages on “ribbons of parchment that were bound spirally around a cylindrical staff.” The receiver placed the received parchment on an identical staff in order to decipher its message.

More recently, World War I initiated a re-emergence of the tactical importance of cryptography, a fact that was signaled clearly by the founding of the U.S. Army Cipher Bureau. In the Second World War, the ability of the Allies to crack the Enigma machine, an encryption mechanism developed by Germany, proved to be one of the most pivotal developments of the war. The concept of basic digital computers, particularly the famed Turing Machine, arose as part of the Allied effort to breaking the German codes.

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