Historical ciphers, when they were introduced and their effect

[magnesium]

I will elaborate on this in a presentation at this year's Voynich Day—I am finalizing a preprint on the subject—but homophonic substitution ciphers can get you a long way toward Voynich-like properties if the cipher's substitution options are verbose. The fundamental tradeoff is that there must be fewer plaintext letters per VMS token, on average, than the manuscript's appearance would otherwise suggest.

The homophonic substitution ciphers at use in early 15th-century Italy already show experimentation with offering both multiple substitution options per plaintext letter and elaborate "compound glyphs" that substitute for syllables / orthographic bigrams. To get even roughly VMS-like text, a cipher has to build out a more robust set of substitution options and include some procedural wrinkles, but the resulting cipher is not terribly alien in its overall construction. Consider this 1448 cipher from Meister's 1902 study of 15th-century Italian ciphers: You are not allowed to view links. Register or Login to view.
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