The cipher secretaries: cryptography in the Republic of Venice

Few Renaissance powers depended on information as much as the Republic of Venice. Trade, diplomacy and war rested on a network of ambassadors, consuls and informers spread from the Levant to the courts of Europe. To protect that correspondence, and to read that of others, the Serenissima developed one of the most advanced cryptographic organisations of its time, under the direct control of the Council of Ten.

Ambassadors and dispatches

Venetian ambassadors regularly sent dispatches to the Senate, and at the end of their mission presented a report, regarded by historians as a valuable source on the states of Europe. The most sensitive parts of the dispatches were written in cipher, that is with nomenclators combining symbols for letters, nulls and codes for the names of rulers, cities and recurring subjects. The ciphers were changed periodically to reduce the risk of their being compromised.

Giovanni Soro and the school of cipher clerks

The most famous figure of this tradition is Giovanni Soro, who in the early sixteenth century was appointed cipher secretary and worked for decades in the service of the Republic. His fame as a codebreaker spread beyond Venice: according to the sources, the papal court too submitted messages to him for interpretation. He died around 1544, leaving pupils who continued his work.

The cipher secretaries worked in the Doge's Palace, in restricted rooms, and were bound to the strictest secrecy. The Republic's rules provided for young men destined for this service to be trained and tested, and for experts to be rewarded for their results. It was a true career, with a hierarchy and a transmission of skills from master to pupil.

The Council of Ten and state secrecy

The Council of Ten, the body that watched over the security of the state, controlled cryptographic activity and confidential correspondence. It decided which information to keep, which to communicate and which to use against opponents and rivals. Intercepted letters from other states, deciphered by the secretaries, thus entered the complex system of intelligence by which the Republic steered its policy.

This organisation was not unique to Venice: Florence, Milan, Rome and other Italian courts had their own cipher experts, and fifteenth- and sixteenth-century Italy is considered the cradle of European diplomatic cryptography. Venice stood out, however, for the continuity and formality of its service, which remained active, with various transformations, for centuries.

The papers of the State Archives

Many documents of this activity are preserved today in the State Archives of Venice, in the former Frari convent: registers of ciphers, keys, ciphered dispatches with their plain-text transcriptions. These materials have allowed historians to study the evolution of nomenclators and to reconstruct the daily work of the cipher clerks, often made of patience, comparison and memory rather than sudden insight.

Venetian cryptography shows how secrecy was an integral part of the government of the Serenissima. Behind its famous political stability lay also the silent work of men able to protect the Republic's words and to read, when possible, those of others, in an age when a dispatch read in time could be worth more than a fleet.