Steganographia

Johannes Trithemius’s "Steganographia" is a complex work on concealed communication that long seemed to many readers to be a book of magic. Now recognized as an early and influential text in cryptography, it contains elaborate methods for encoding messages, along with learned references to spirits, names, and ritual forms that reflect the intellectual world of late medieval occultism.

Johannes Trithemius (1462–1516) was a German abbot, humanist, and scholar whose writings became influential in Renaissance esotericism. He is especially associated with cryptography, angelology, and occult learning, and his works were widely read by later practitioners of ceremonial magic.