Giovan Battista Bellaso

Giovan Battista Bellaso (1505 – between 1568 and 1581) was an Italian cryptologist, born in Brescia. The Vigenère cipher is named after Blaise de Vigenère, although Giovan Battista Bellaso had invented it before Vigenère described his autokey cipher.

Biography Bellaso was born of a distinguished family in 1505. His father was Piervincenzo, a patrician of Brescia, owner since the 15th century of a house in town and a suburban estate in Capriano, in a neighborhood called Fenili Belasi (Bellaso's barns), including the Holy Trinity chapel. The chaplain was remunerated each year with a regular salary, and a supply of firewood. The family coat of arms was ‘‘On a blue field three red-tongued gold lion heads in side view”.

Bellaso received a degree in civil law at the University of Padua in 1538. 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.

Works 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.

La Cifra del Sig. Giovan Battista Bellaso

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. Encipherment is performed by using an agreed-upon phrase called countersign, placed over the plaintext. With reference to the table, one substitutes the plaintext letter with the letter that is above or under it in the alphabet identified by the capital letter of the countersign. Enciphering: VIRTVTIOMNIAPARENT VIRTVTIOMNIAPARENT VI Countersign larmataturchescapa rtiraacinquedilugl io Plaintext SYBOVEYLDANVOFSZLP IINCVPNSHMLRNXOIZN RD Ciphertext Deciphering: VIRTVTIOMNIAPARENT VIRTVTIOMNIAPARENT VI Countersign SYBOVEYLDANVOFSZLP IINCVPNSHMLRNXOIZN RD Ciphertext larmataturchescapa rtiraacinquedilugl io Plaintext This cipher is a letter-by-letter polysubstitution using a long literal key string. It is very similar to the Vigenère cipher, making many scholars call Bellaso its inventor, although unlike the modern Vigenère cipher Bellaso didn't use 26 different "shifts" (different Caesar's ciphers) for every letter, instead opting for 13 shifts for pairs of letters. The system is still periodic although the use of one or more long countersigns makes it sufficiently secure. This feature is perfectly in line with Kerckhoffs's principle.

Novi et singolari modi di cifrare Bellaso's second booklet 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. Arma uirumque cano troie qui primus ab oris Long countersign: Qui confidunt in Domino etc... Enciphering: QQQQ UUUU IIII ... Countersign Giul ioCe sare ... Plaintext NQHP MSGN XDYT ... Ciphertext

Il vero modo di scrivere in cifra

Bellaso's third book 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. The encipherment is performed word-by-word or one letter at a time.

Editions La cifra (in Italian). Venezia. 1553. Novi et singolari modi di cifrare (in Latin). Brescia: Lodovico Britannico (1.). 1555. Il vero modo di scrivere in Cifra con facilità, prestezza, et securezza di Misser Giovan Battista Bellaso, gentil'huomo bresciano, Brescia, 1564.

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