Babbage and cryptography. Or, the mystery of Admiral Beaufort's cipher

If Charles Babbage had written the book (The Philosophy of Decyphering) he planned to do, he would have been the first to publish a routine solution of the Vigenère cipher, the “chiffre indéchiffrable” of more than two and a half centuries. For before any known publication, and by a wide margin, he made three important discoveries, namely, the mathematical law of this cipher, the principle of the key periodicity, and the technique of the symmetry of position. These achievements as well as Babbage's possible role during the Crimean War as a cryptographical adviser to his friend, Rear-Admiral Sir Francis Beaufort of the Admiralty, form the topic of this article.