Trithemius's Steganographia: Cryptography Disguised as Magic

Few works have fuelled as much suspicion as the Steganographia of Trithemius. Begun around 1499, while the author was still abbot of Sponheim, it presented itself as a treatise on sending messages over distances with the help of spirits, complete with long lists of angelic names and solemn formulas. For more than a century it circulated only in manuscript, trailing the reputation of a demonic book.

A Letter That Fell into the Wrong Hands

Trithemius described the project in a letter to his Carmelite friend Arnold Bostius, who died before receiving it. The letter was read by other clerics and circulated, causing scandal. The French philosopher Charles de Bovelles, who had visited Sponheim in the first years of the sixteenth century and leafed through the manuscript, later described the work as full of demons' names and judged it dangerous.

From then on Trithemius repeatedly had to defend himself against the charge of necromancy. His later works, such as the Antipalus maleficiorum of 1508, a treatise against witchcraft, can also be read as an attempt to present himself as an orthodox theologian and an enemy of illicit magic. It condemns the magical practices of the time and the books that spread them, pointing to the means offered by the Church as the only legitimate remedies.

The Secret of the Third Book

Some sixteenth-century readers already suspected that simple cipher systems lay behind the names of the spirits. In the first two books, indeed, the supposed invocations turn out to be hidden messages that can be decoded with precise rules: only one letter in so many counts, for example. The third book, shorter and unfinished, seemed instead genuinely astrological and magical, with tables of planets and celestial intelligences.

In the 1990s two scholars, the German Thomas Ernst and the American mathematician Jim Reeds, showed independently that the numerical tables of the third book also contain enciphered texts. The Steganographia thus appears, at least in large part, as a manual of cryptography disguised as a book of magic, although the question of how far Trithemius believed in its spiritual component remains open.

From the Polygraphia to the Index

The work on cryptography that Trithemius chose to make public was the Polygraphia, printed in 1518, two years after his death, and often regarded as the first printed book devoted entirely to ciphers. It contains the famous tabula recta, a table of shifted alphabets that anticipates the polyalphabetic systems of later centuries. The book went through several editions and, as early as 1561, a French translation.

The Steganographia reached print only in 1606, in Frankfurt. A few years later, in 1609, it was placed on the Index of Forbidden Books. Before that, many curious readers had sought copies: John Dee, finding a manuscript in Antwerp in 1563, wrote to William Cecil to point out the exceptional value of the book and to ask for support so that he could copy it.

The story of the Steganographia shows how thin the line between technical secret and magical secret was in the early sixteenth century. A system for hiding messages could look like a conjuration, and an apparent conjuration could conceal a code. This ambiguity, whether or not the author intended it, has made Trithemius a key figure in the history of cryptography as much as in that of occult literature.