Steganography: The Art of Secret Writing

...and day, except for one who acts as a messenger to the presiding Spirits: they are all good and benevolent, and they do not harm the practitioner unless he is malicious or unskilled in the art. It is not necessary to summon them all at once; a few are sufficient, and sometimes one is enough to satisfy the practitioner, whether the operation takes place by night or by day. For since they are benevolent, quiet, and tranquil, they are more often solitary than rowdy in a crowd. Therefore, when you wish to work through them and disclose the secret of your mind to someone—no matter how distant—through their agency, do as follows: Write on paper previously prepared in the proper manner, as you know, whatever narrative you wish and in whatever language; for it does not matter, because the recipient is not intended to perceive your mind from the paper, but from the Spirits. While writing, turn yourself toward the East original: "subsolanum," referring to the direction of the East Wind, and when finished, recite this conjuration:

Padiel aporsy mesarpon omeuas peludyn malpreaxo.
Condusen, vlearo thersephi bayl merphon, paroys gebuly ma-
ilthoniyon ilthear tamarson acrimy lon peatha Casmy Cher-
tiel, medony reabdo, lafonti iaciel mal atti bulomeon abry pa-
thulmon theoma pathormyn.

While presented as a magical incantation, these "spirit names" and "words of power" are actually a cover for a cryptographic system. In Trithemius's method, the actual message is hidden within these nonsense words through a specific letter-replacement code.

When you have completed these words, you will see two, or at least one, of the Spirits calmly present and ready to obey your will. Commit your secret to him, and he will faithfully carry it to the place you commanded. When the letters have come to the person to whom they were sent via the messenger: if he is alone, it is well; if he is with others, let him withdraw to the side if he can. If he cannot, let him turn toward the East and say this conjuration in silence:

Padiel ariel vanerhon chio tarson phymatto merphon ampriscoleda-
barym, elsophroy mesarpon amcorsy, paneryn atle pachunigel
thearan vtrul vt solubito beslonty las gomadyn triamy mesar-
nothy.

Once these words have been duly spoken, the sent Spirit will immediately appear, revealing to him perfectly—with no one else perceiving it—whatever you committed to be revealed, without deceit and without any danger. However, no one who is malicious or wicked will easily be able to work in this art; but the better and purer a person is, the more willingly the Spirits... The text cuts off mid-sentence; likely "will serve him."