Delastelle
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Félix-Marie Delastelle (1840-1902) is remembered for a short but influential book which appeared in the last year of his life: Le Traité élémentaire de cryptographie, Gauthier-Villars, Paris, 1902.
Kahn claims that "Delastelle invented a fractionating system of considerable importance in cryptology." (The Codebreakers, page 243). The names of the ciphers associated with Delastelle are principally the Bifid cipher and the Trifid cipher. His Four-square cipher is a variant on the earlier Playfair cipher.
Delastelle may have been unaware of Playfair, but he had read of the fractionating cipher described by Pliny Earle Chase in 1859. The first presentation of the bifid appeared in the French Revue du Génie civil in 1895 under the name of cryptographie nouvelle.
There are few biographical details. Félix-Marie's father, a master mariner, was lost at sea in 1843. Félix attended the College of Saint-Malo and then worked in the local port as a bonded warehouseman for forty years. After retirement, in 1900, he rented a single room in a holiday hotel where he wrote a 150 page book. On hearing news of his brother's sudden death, he collapsed and died in April 1902.
Delastelle is unusual for being an amateur cryptographer at a time when significant contributions to the subject were made by professional soldiers, diplomats and academics.
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