I have been looking into Steganographia for some time. According to Dan Harms review of Skinners edition it has completly ignored cryptography providing only translation based on a late french manuscript copy. There is one surviving manuscript attributed to John Dee. Text itself isn't interesting, very repetitive and formulaic. Trithemius just wanted to pad out his book. Only Spirits from chapters 1-16 Book 1 have some specific tasks attributed to them, like these carry love secrets, those carry secrets about treasure. In chapters 21-31 Book 1 every time spirits appear in a monstrous form its a snake with a head of a woman. In Book 2 sometimes he claims that he got his info from "Raziel" or "Solomon, the hebrew Hermes" or "Picatricem".
Cryptographic meaning of the book was obvious since 1606 because all printed editions came with "
Clavis Steganographia" and "
Clavis Generalis Triplex" that gave short description of encryption methods with examples and solutions (different then those in Steganographia itself), but they did not explain the spirit conjurations. Those were first revealed in 1624 by duke August II of Brunswick aka "Gustavus Selenus" in his book "
Cryptomenytices et Cryptographiae", which was translated into english in 1900 but never published.
For spirit conjurations take every other word, then take every other letter to receive an instruction how to hide your secret. First and last words never contain important letters. Printed editions sometimes had errors in them that made it impossible to read secret messages in conjurations. Tables with spirit names and numbers are hints to each method. In Book 2 first letters from the name of spirits hide substitution ciphers for a 22 letter alphabet.
Best edition explaining the cryptography has to be one by Wolfgang Heidel, first published in 1676 and reprinted in 1721. It has all the answers intervowen in the text (missing some illustrations). Every message hidden in spirit conjurations is given right after it, every example letter has hidden message highlighted with upper case letters. Even not knowing latin (or sometimes german} its not hard to figure out. Heidel claimed he solved Book 3 but has hidden answers in his own code. Only in the '90 when Thomas Ernst and Jim Reeds published articles on it secrets of Book 3 were made public. Its based on a substitution cipher alphabet of 25 symbols where every spirit has different number range.
Trithemius multiple times states that you have to send a "clean" letter "which hides nothing" to a friend marked with a symbol of the spirit, so they know which encryption method you used.
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