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The dispatch of the ambassador to Paris Pietro Duodo of 12 August 1595, the last so far found that uses Partenio's cipher 5. At the last visible line the dispatch continues using the ordinary cipher, the ziffra granda. [ ASVE, Senato Dispacci di ambasciatori in Francia, f. 24, c. 34. Any commercial use of this image is prohibited.]

Pietro Partenio, a notary and one of the most brilliant Venetian cryptologists, certainly knew Hieronimo di Franceschi deputy for the ciphers for the CX*, who had repeatedly been his client as seen on his notarial deeds. He took up the two most original ideas of Franceschi, the one of super-encryption and the one of a fake key. Partenio criticized the Venetian ciphers in use in those years, including Franceschi's cifra delle caselle, considered the safest of them all.

In June 1595 the CX faced with the news that François Viète had boasted to be able to decrypt the caselle, ordered to use from now on a cipher of Pietro Partenio. The fifth cipher was chosen from those presented by Partenio to the CX in the years 1592-1593, and a week later the CX sent the cipher key to the ambassador in Paris, with the recommendation to use this cipher for the most reserved parts of the dispatches.

At the bottom of this page you can encrypt using this cipher inside an interactive window.

The key of the cipher is double: a three digits nomenclator, which begins with the letter A encrypted with 100 and continues in a more or less orderly manner, as in the figure on the right, showing the very first beginning of the encrypting list, and a small super-encryption list converting digits into letters.

Numeri

0	1	2	3	4	5	6	7	8	9
l z	a m	b n	c o	d p	e q	f r	g s	h t	i u

The encrypting procedure consists of two successive steps:

1. Encrypt the text to be sent using the encrypting list. Use words, syllables or individual letters.
2. Encrypt a second time by replacing each decimal digit with a letter chosen between two homophones from the list shown on the right, which is the one of 1593 and well ordered; for instance A, encrypted with 100, can be super-encrypted in one of eight possible combinations: all alz azl azz mll mlz mzl mzz.

   
   

   Numeri

   0	1	2	3	4	5	6	7	8	9

   In June 1595 a scrambled list, visible on the right, was sent to the embassy in Paris. The nomenclator of 1595 was also different from that of 1593, except for the first letter A that is again encrypted with 100, giving eight possible combinations: chh chp cph cpp thh thp tph tpp .

• For each letter, look for the corresponding number in the key list, and write it down, in groups of three;
• For each three-digit number obtained, seek in the scontro (deciphering list) to recover the plain text.

It could be argued that this cipher could be simplified in one single operation, a nomenclator with eight homophones for each letter or syllable or word; for instance the letter A would be encrypted with one of the eight homophones: chh chp cph cpp thh thp tph tpp .

But there are a few good reasons in favor of a two-step encryption:

• The nomenclator of numbers is less cumbersome and the table can be written on a piece of paper or, even better, can be remembered by heart.
• If even the nomenclator sheet should fall into enemy hands, the secrecy of the cipher would be preserved, thanks to the over-encryption list, that had to be kept in memory; and this was the main goal of Partenio.

This cipher is not the most complicated and sophisticated of Partenio, and perhaps it was chosen by the CX for its simplicity.

Unfortunately, the secretaries in charge of the cipher did not appreciate, in particular the one in Paris, who first used it. The three dispatches from Paris, in July-August 1595, using this cipher for limited portions, the most secret and reserved, have errors and cancellations, a sign that the secretary did not find it so simple to use and after the third attempt he did not use it anymore.

To date, no other dispatches have been found in the Venetian archives that use Partenio's ciphers.

The original key of the cipher found in the archive. [ ASVE, Cifre, chiavi e scontri di cifra, con studi successivi, sec XVI-XVIII, busta 2, fascicolo 13 Cifre di Pietro Partenio, foglio sciolto. Any commercial use of this image is prohibited.]

Many months after having partially recovered the key of this cipher, among the papers of Pietro Partenio, I found the original sheet with the key, the handwriting looks the one of Partenio, it had been overlooked, hidden among other sheets. it was thus possible to recover the whole cipher.

• Armand Baschet, Les Archives de Venise - Histoire de la chancellerie secrète, Henri Plon, Paris, 1870 − 1870, pag. 578 - 579 → eBook
• Paolo Bonavoglia, “The cifra delle caselle a XVI Century superencrypted cipher”, Cryptologia, Taylor & Francis, Philadelphia, 2019 − 2019 → info
• David Kahn, The codebreakers, Scribner, New York, 1967 − 1996, pag. 117 - 118 → eBook
• Maria Pia Pedani, Veneta auctoritate notarius. Storia del notariato veneziano (1514-1797), Giuffrè, Milano, 1996 → eBook
• Luigi Sacco, Un primato italiano: la Crittografia nei secoli XV e XVI, Roma, 1958, pag. 24 → eBook