[zipwitch]

Mentioning cryptography and magic makes me think of Steganographia written in 1499 by Johannes Trithemius.

https://en.wikipedia.org/wiki/Steganographia

"Trithemius' most famous work, Steganographia (written c. 1499; published Frankfurt, 1606), was placed on the Index Librorum Prohibitorum in 1609 and removed in 1900. This book is in three volumes, and appears to be about magic—specifically, about using spirits to communicate over long distances. However, since the publication of a decryption key to the first two volumes in 1606, they have been known to be actually concerned with cryptography and steganography. Until recently, the third volume was widely still believed to be solely about magic, but the "magical" formulae have now been shown to be covertexts for yet more cryptographic content."