Johannes Trithemius, Steganographia

The Steganographia of Johannes Trithemius demonstrates how to concel a plaintext in pretended conjurations of spirits. Because of the controversy it aroused, though written in 1500 it was not printed until 1608 and then placed on the Index of forbidden books. The cryptologist Gustavus Selenus discusses it in his Cyrptomenices, citing a variant text which may well be superior to that of 1608.

First printed text (1608)