GoKawiilIn April 1542 a letter left Rome for the court of Charles V in Spain. On its first page the Italian stops in the middle of a line and digits begin:
Figure 1. The opening of the cipher, f. 70r. Archivio Apostolico Vaticano (AAV), Segr. Stato, Spagna 1A, photograph supplied through DECODE record 92. Detail enlarged from the photograph.
Read with the key recovered below, the first ten digits group like this:
73 4 57 4 9 03 5 d o p o · l a
Dopo la, "after the". The 9 stands for nothing: it is a null. The difficulty is deciding where each code ends. 73 is d, but 7 3 is also two letters, n m. Even with the key, a run of digits can be read more than one way.
Two problems follow: finding the key without knowing where one code ends and the next begins, and then, once a key exists, telling the writer's words from a plausible guess.
The letter
The sender was Cardinal Alessandro Farnese, grandson of Paul III and, at twenty-one, head of the papal secretariat. The recipient was Giovanni Poggio, bishop of Tropea and nuncio, the Pope's ambassador, at the Emperor's court. The letter opens in ordinary Italian: Poggio will have heard by word of mouth from Giovanni Ricci da Montepulciano about la materia della pace, the peace between the Emperor and France, so Farnese will not repeat it. Montepulciano had returned from Spain in February with the Emperor's terms and had left Rome for Spain again in late March.
Montepulciano's name is also on a cipher key. Aloys Meister's 1906 study of papal cryptography prints, among the old ciphers of the papal secretariat, a key headed Cifra ultima con Mons. Poggio mandata per il Montepulciano: the latest cipher with Poggio, sent by Montepulciano. Meister dates it 1538–42.
The letter fills eight pages on four leaves, 70r to 73v in the archive's numbering: r for the front of a leaf, v for the back. Page 70r is cleartext for most of its length. Then the digits take over in the middle of a line and fill the whole of pages 70v to 72r. On 72v they surround a cleartext passage about church business and news from Ancona, "fresh and from a good source". The cipher ends on 73r, and the rest of that page is clear. Page 73v is clear and dated Da Roma alli X[?] di Aprile 1542: the day is a Roman numeral beginning with X whose remaining strokes lie under a flourish, still unread. What is in clear is the frame; the instructions are in cipher.
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