This cipher was used by Venetian diplomacy between 1625 and 1630, and is still the only variable-sized cipher found in the Venice state archive. Two decrees of the Council of Ten (CX) of the end of 1624, state that having been intercepted the current cipher, a new one is needed; in the CX deed of December 10 the cipher proposed by Ottavian Medici * , deputy for the ciphers, is approved, and it is ordered that the cipher is sent to all the Venetian embassies and representatives; there is no attachment with description and instructions, but there seems to be no doubt that this is the aforementioned cipher, because the first messages encrypted with it are dated at the beginning of 1625.
The Venetian ciphers of the time typically consist of an alphabet, a syllabary and a dictionary. The ciphering signs are numbers of two, three or four decimal digits and they must all be written at a constant distance so that the cryptanalyst is not able to distinguish the different encrypting signs. Of course, one has to allow the legitimate recipient be able to do so. In the analogous Vatican ciphers of Matteo Argenti one relied on the context, trusting that ambiguous cases would not occur.
Ottavian Medici made a different choice: two decimal digits, 5 and 6, are used only as initials and therefore allow us to easily distinguish the various signs. The decipher function is unique. A similar rule was used three centuries later in the twentieth century, in the straddling checkerboard . As mentioned above, Medici recommended writing the numbers all attached, as in the example on the right.
Among the cipher keys kept in the State Archives of Venice, the scontro (key sheet) of this cipher was not found; the following was recovered by the writer on the basis of the dispatches with deciphers found in the archives. Below you find the cipher alphabet, completed with the rarest letters, B F Q Z , absent from the texts, using the regularity of the pattern, and the first line of the syllabary also completed this way.
The table above shows clearly this regular pattern. The reconstruction of the alphabet and the syllabary was easy once the rule of the pattern was recovered. This is a weakness, because the syllabary is by far the most used part of Venetian ciphers. It would be interesting to know if this cipher had been decrypted by some European cryptanalysts of the time. The cipher also includes a dictionary with dozens of words, perhaps hundreds.
This cipher was used for a few years, there are many dispatches encrypted by several Venetian embassies in European capitals; some follow the CX recommendations and the digits are written without interruptions as in the example above, while others have cipher groups well separated by spaces, as in the example on the right, thus frustrating the basic idea of this cipher. The insufficient training of the cipher operators shows also in this case the most frequent flaw in the history of cryptography.
Three CX minutes of January, March and April of 1630, denounce the possibility that the key of this cipher had fallen into alien hands and therefore a change of the cipher was necessary; on April 26 a new cipher was approved, again designed by Medici with the collaboration of two other men in charge for the ciphers, Pietro Amai and Antonio Marin. The resolution contains the order for the immediate adoption of the new amount, by ambassadors, residents, public representatives. Indeed the adoption was not so immediate, the previous cipher was still in use by some embassies, at least until the end of 1631.
The ciphers adopted in the following decades were more and more simple and regular; encrypting signs were almost always of fixed size, usually 3 digits; any way the recommendations to write all digits without any separator remained and some trick to conceal the size were also recommended: for instance to insert nulls of 1 or 2 digit at the beginning, or at the end of each line.
Below you can try this cipher; enter text in the window, then click "Encrypt". Do not insert texts that are too long. It should be noted that in case of homophones, to follow the recommendations to change homophones, the encrypting function use a random number generator, so the results may be variable.
Cifra Medici 1624
Ottavian Medici was a brilliant pupil of Pietro Partenio, and was for more than twenty years in charge for the ciphers for the CX. He took up some ideas of Partenio, in particular the nomenclators of numbers only like this, but he gave somehow priority to ease of use; the ciphering lists were largely ordered, while super-encryption and fake key, the two advanced techniques favored by Partenio, were forgotten, presumably because too complicated.
The name Ottavian is here adapted to the modern spelling; in the CX documents it is variously written as Ottauio, Ottauian, Ottauiano; in the description of the 1645 cipher his signature appears, almost certainly autograph, since the handwriting is different from that of his colleague Padauin on the previous line. And here Ottauian is clearly readable. So "Ottavian" seems the best choice in English.
Attention please! Venetian ciphers used the 20 letters XVI century Latin/Italian alphabet, that is different from the modern 21 letters Italian one, for in Latin there was a single letter, uppercase V and lowercase u, so you must write u instead of v, otherwise the letter is ignored. The j k w x y letters are also ignored.