Steganographia is a late 15th / early 16th century German book of magic… but it’s not actually about magic.
Right around the turn of the 16th century, a German abbot named Johannes Trithemius wrote a book called Steganographia. Trithemius was a polymath, historian, and dubious scholar. (Dubious? Well, he wrote a chronicle of an abbey’s history, for example, but inserted his own fictional events and sources.) He became an abbot when he was 21 years old, left his abbey when he was 44, and spent much of his time assembling libraries and writing books.
Steganographia was written around 1499 or 1500, and at first glance it appears to be a book of magic spells and incantations:
Bvriel mastfoyr chamerusyn, noel peam Ionachym mardusan philarsij, pedarym estlis carmoy boycharonti phroys fabelronti, mear Laphany vearchas, clareson, notiel, pador aslotiel, marsyno reneas, Capedon, thisinasion melro, lauair carpentor, thurneam camelrosyn.
When you say this song in silence, always looking at the earth: the summoned spirits will be present. But do not be afraid, because they will not be able to harm you if you are strong and unwavering in mind. These princes, or spirits, are supposed to report all the secrets of the night during the night; yet they are the most apt and willing to bring a message into prisons for prisoners; practical and loving; and to all the things that are done in the night, whether it be good or bad, because they hate the light.
Steganographia (via Google Translate)
Trithemius never published this book. Copies of it circulated around Europe, though. The famous occultists Heinrich Cornelius Agrippa (along with Paracelsus, a student of Trithemius) and John Dee had copies. More than a century after it was written, and long after Trithemius’ death, it was finally officially published. And just three years after its publication, Steganographia was predictably banned by the Vatican for heresy.
However, Steganographia is not actually a book of magic. Hidden within the seemingly-occult text is something else. It’s a textbook on steganography (the art of hiding words within unrelated text) and cryptographic ciphers. The book itself is a demonstration of those techniques: each one of Trithemius’ “spells” is in fact some plain writing in disguise, a how-to guide disguised by the very techniques it teaches. Take the fake words in a spell and read only every second letter, for example, and a new and mundane text appears.
Now, this was not exactly a secret; the 1606 printing of Steganographia was accompanied by a guide explaining just how the ciphers worked. Except that it only explained the first two sections of the book; the third was deciphered by an American mathematician named Jim Reeds in 1998:
Book III of Trithemius’s Steganographia (written ca. 1500) contains hidden cipher messages within what is ostensibly a work on magic. After almost 500 years these cryptograms have been detected and solved. (Since 1606 it was known that similar ciphers were present in Books I and II.) As a result the Steganographia can no longer be regarded as one of the main early modern demonological treatises but instead stands unambiguously revealed as the first book-length treatment of cryptography in Europe.
Solved: The ciphers in book III of Trithemius’s Steganographia
[Thanks to Nik]
The Generalist Academy 
