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.

Who will divine, what Trithemius wrote in this third book of Steganography, and what he would have written?

Wolfgang Ernest Heidel (Steganographia vindicata, 1676)

…the Steganographia is, at least on first reading, deeply ambiguous. The work itself seems to be about using spirits—angels and demons—to send secret messages. But the preface to Book 1 of the Steganographia explains that the cryptographic techniques are purely natural. These are valuable techniques of statecraft and in order to keep them out of the hands of the enemies of the state (planning conspiracies) and adulterers (planning trysts) they are disguised by the use of a figurative language of demonology.

Most readers of the Steganographia have chosen to ignore its preface, discounting it as the author’s evasive attempt to protect his demonology book from criticism…These two different readings of the Steganographia have given rise to a long-running controversy about Trithemius’s role in the rise of interest in magic and Hermeticism in the Renaissance: is the Steganographia primarily an exposition of cryptographic techniques disguised as angel magic, or is it primarily a magic work disguised as cryptography?

…Selenus [background] was unable to supply a cryptographic interpretation to Book 3 of the Steganographia, but in case some future reader might make sense of it, he reprinted the entire Book 3 in his book.

Selenus’s account of the Steganographia was followed by essentially all 17^th century German books on cryptography: both purely technical treatises and Trithemius apologetica. These books—whose titles often contain phrases like Trithemius vindicated—explain the Steganographia as cryptography and thereby acquit its author of magic. In one such book, published in 1676 in Mainz, Wolfgang Ernest Heidel [an obscure clerk drawing on Selenus’s work] claims to have discovered the true cryptographic meaning to Book 3, and presents it in the form of a series of cryptograms. It is easy to guess that Heidel was bluffing, hoping to gain the glory for figuring out what Trithemius was doing in Book 3 without actually doing the work.

…In the following sections of this paper I describe the contents of Book 3 in greater detail, outline the steps by which I found and solved cryptograms in Book 3, and sketch some implications this discovery has for the study of the Steganographia and its author.

[media] After submitting this paper for publication I became aware of a long article by Thomas Ernst, “Schwarzweisse Magie: Der Schlüssel zum dritten Buch der Steganographia des Trithemius”, Daphnis: Zeitschrift fur Mittlere Deutsche Literatur 25, no. 1 (1996_28ya): 1–205 [a version was published in English in 1998], which was also published as a separate book (Amsterdam: Rodopi, 1996). In this magisterial article Ernst reaches exactly the same cryptographic conclusions that I did, but 3 years earlier, and in greater detail. [Chronology: I received my Steganographia photocopy on 2 March 1998, had my first plaintext on 5 March, the first draft of this paper on 9 March, learned about the existence of Ernst’s paper on 1 April 1998 and received confirmation that it indeed solved Trithemius’s Book II cipher on 3 April.] Ernst, working from manuscript copies of Book 3 in Wolfenbüttel and in the Vatican, for which he provides a critical edition, is able to complete the sentence in Table D. He too sees the cipher of Book 2 as a transitional form between the monoalphabetic ciphers of classical antiquity and the middle ages and the truly polyalphabetic ciphers of Trithemius’s Polygraphia. Ernst persuasively argues that the Clavis Steganographiae is an earlier version or draft of the Steganographia. Finally, Ernst was able to solve Heidel’s cryptograms, which show that Heidel had indeed also solved Trithemius’s Book 3 ciphers.

Thus “Thomas Ernst” is the answer to Heidel’s question, quoted as the epigraph of this paper.