Félix-Marie Delastelle (2 January 1840 – 2 April 1902) was a French cryptographer, best known for inventing the

bifid cipher In classical cryptography, the bifid cipher is a cipher which combines the Polybius square with transposition, and uses fractionation to achieve diffusion. It was invented around 1901 by Felix Delastelle. Operation First, a mixed alphabet Po ...

, first presented in the ''Revue du Génie civil'' in 1895 under the name of "cryptographie nouvelle". This cipher combines

fractionation Fractionation is a separation process in which a certain quantity of a mixture (of gases, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in which the ...

with transposition, and was an early cipher to implement the principles of confusion and diffusion. David Kahn described it as a "system of considerable importance in cryptology." Delastelle's other polygraphic substitution ciphers included the trifid and

four-square cipher The four-square cipher is a manual symmetric encryption technique. It was invented by the French cryptographer Felix Delastelle. The technique encrypts pairs of letters (''digraphs''), and thus falls into a category of ciphers known as polygraph ...

s.Delastelle, p. 77. The last of these is a variant on the earlier

Playfair cipher The Playfair cipher or Playfair square or Wheatstone–Playfair cipher is a manual symmetric encryption technique and was the first literal digram substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of ...

: Delastelle may have been unaware of Playfair, but he had certainly read of the fractionating cipher described by

Pliny Chase Pliny Earle Chase (18 August 1820 in Worcester, Massachusetts – 17 December 1886 in Haverford, Pennsylvania) was an American scientist, mathematician, and educator who contributed to the fields of astronomy, electromagnetism, and cryptograph ...

in 1859. 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 until 1860. After leaving school, he worked in the local port, as a bonded warehouseman, for forty years, and pursued his interest in amateur cryptography as a hobby. Following his retirement in 1900, he rented a single room in a holiday hotel where he wrote a 150 page book ''Traité Élémentaire de Cryptographie'' which he completed in May 1901. On hearing news of his brother's sudden death, he collapsed and died in April 1902. His book appeared three months later, published by Gauthier-Villars of Paris. 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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* {{DEFAULTSORT:Delastelle, Felix Pre-computer cryptographers French cryptographers 1840 births 1902 deaths