Trithemius and the Polygraphia: the first printed book on cryptography

Johannes Heidenberg, known by the Latin name Trithemius after his birthplace, Trittenheim on the Moselle, was one of the most unusual figures of the German Renaissance. Born in 1462, he became abbot of the Benedictine monastery of Sponheim at a very young age and turned it into a renowned centre of learning thanks to a library of thousands of volumes. He died in 1516 in Würzburg, where he headed the abbey of St James.

An abbot between history and secrets

Trithemius wrote chronicles, catalogues of ecclesiastical writers and works of monastic spirituality, but his fame, even in his lifetime, was tied to more restless interests: natural magic, the names of angels, hidden writing. The young Cornelius Agrippa visited him and dedicated to him the first draft of the De occulta philosophia, while Paracelsus named him among his teachers. He corresponded with humanists all over Europe.

The Polygraphia

The Polygraphia, in six books, was completed around 1508 and dedicated to Emperor Maximilian I. It was printed only in 1518, two years after the author's death, and for this reason it is considered the first printed book devoted entirely to cryptography. Unlike the Steganographia, which would cause a scandal, the Polygraphia presents its methods openly, without angelic or demonic veils.

The first book contains a surprising system: hundreds of tables in which each letter of the alphabet corresponds to a Latin word. By choosing one word for each letter of the message, one obtains a text that looks like a devout prayer. This cipher, which historians call the Ave Maria because of its tone, combines substitution and concealment: whoever intercepts it believes he is reading a harmless religious text.

The tabula recta

The fifth book introduces the tool that made Trithemius famous among cryptographers: the tabula recta, a square made up of all possible alphabets, each shifted by one place relative to the previous one. The first row is the normal alphabet, the second begins with B, the third with C. Trithemius proposes enciphering the first letter of the message with the first row, the second with the second, and so on.

It is a progressive polyalphabetic cipher, in which the alphabet changes with each letter in a fixed order. The system is weak, because the rule is always the same and there is no variable secret key, but the table itself would become the basis of later methods. Bellaso and Vigenère would use exactly this kind of square, guided however by an agreed keyword.

The legacy of a pioneer

The Polygraphia went through numerous editions and a French translation by Gabriel de Collange, published in 1561. It was read by diplomats, secretaries and the curious, and helped spread across Europe the idea that secret writing was a discipline with its own rules, worthy of a treatise. The very word polygraphy, “manifold writing”, indicated the variety of possible systems.

Trithemius remains a figure suspended between two worlds: a learned monk and a seeker of secrets, a historian and, in the eyes of his contemporaries, a magician. In the Polygraphia, however, it is mainly the technician who speaks, and his tables accompanied cipher clerks for centuries, long after the controversies over his reputation had died down. The tabula recta in particular remained an everyday working tool until the twentieth century.