Giovan Battista Bellaso

From the longer Wikipedia page which contains examples of the ciphers.
Giovan Battista Bellaso (Brescia 1505–...) was an Italian cryptologist.
The French author, Blaise de Vigenère, reported that he was serving as a secretary in the suite of Cardinal Rodolfo Pio di Carpi and credited him with the invention of the reciprocal table, now called the Della Porta table. However, Bellaso never mentioned Cardinal Pio in his books and explained that in 1550 he was in the service of Cardinal Duranti in Camerino and had to use secret correspondence in the state affairs while his master was in Rome for a conclave. Versed in research, able in mathematics, Bellaso dealt with secret writing at a time when this art enjoyed great admiration in all the Italian courts, mainly in the Roman Curia.
In this golden period of the history of cryptography, he was just one of many secretaries who, out of intellectual passion or for real necessity, experimented with new systems during their daily activities. His cipher marked an epoch and was considered unbreakable for four centuries. As a student of ciphers, he mentioned among his enthusiasts many eminent gentlemen and ‘‘great princes’’. In 1552, he met count Paolo Avogadro, count Gianfrancesco Gambara, and the renowned writer Girolamo Ruscelli, also an expert in secret writing, who urged him to reprint a reciprocal table that he was circulating in loose-leaf form, in print and manuscript. The table was to be duly completed with the instructions. Copies of these tables exist in contemporary private collections in Florence and Rome.
Polyalphabetic substitution with mixed alphabets, frequently changed without a period, is attributed to Leon Battista Alberti, who described it in his famous treatise De cifris of 1466. This crucial invention has a limit in that it obliges the encipherer to indicate, within the body of the cryptogram, the index letters determining the choice of the next alphabet. It was Giovan Battista Bellaso who first suggested identifying the alphabets by means of an agreed-upon countersign or keyword off-line. He also taught various ways of mixing the cipher alphabets in order to free the correspondents from the need to exchange disks or prescribed tables.
In 1553 he published his first and most important booklet: La Cifra del Sig. Giovan Battista Bel[l]aso, dedicated to Girolamo Ruscelli. For the implementation of this cipher a table is formed by sliding the lower half of an ordinary alphabet for an apparently random number of places with respect to the upper half. Actually the table can be compiled by heart by moving the lower list one place to the right following the alphabetic order of the index letters, firstly the vowels, then the consonants: A, E, I, O, V, C, G, M, Q, S, Y.
 
Bellaso’s second booklet, Novi et singolari modi di cifrare, appeared in 1555 as a continuation of the first. The lower halves of the alphabets are now shifted regularly, but the alphabets and the index letters are mixed by means of a mnemonic key phrase, which can be different with each correspondent.
Bellaso’s third book, Il vero modo di scrivere in cifra, was printed in 1564 and dedicated to Alessandro Farnese. It recapitulates the preceding ciphers, with many new variations with regard to their usage. All tables are used with or without countersigns or index letters. 
Bellaso challenged his detractors to solve some cryptograms encrypted according to his guidelines. He also furnished the following clue to help the solution of one of them: ‘‘The cryptogram contains the explanation why two balls, one in iron and one in wood, dropped from a high place will fall on the ground at the same time.’’ This is a clear statement of the law of the free-falling bodies forty years before Galileo. Nobody has yet solved the cryptogram, and Bellaso’s demonstration is still unknown.
See also the Ciphermysteries page . There are a number of other websites, eg and .
Category:Biographies
category:16th century