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Historical ciphers, when they were introduced and their effect - Koen G - 20-05-2025
After having read the paper by Marco Vito that was highlighted by Mark here: You are not allowed to view links. Register or Login to view. , I feel like we need a to the point overview of which ciphers were used in the 15th century, when they were introduced and what their effects would be. Could they make a plaintext more like Voynichese, or do they have an opposite effect?
Your input, additions and corrections will be very much required and appreciated. If this turns into something decent, I can make an easy to find version of it in the curated subforum. This might be helpful for newcomers.
1) Simple substitution.
- Each letter of the plaintext consistently corresponds to a symbol of the ciphertext. (Example: Caesar cipher).
- Existed before the 15th century.
- Popular with solvers, but there is a broad consensus among scholars that the Voynich text is not the result of a simple substitution cipher.
2) Introduce nulls.
- Some extra characters in the ciphertext don't correspond to anything. This can be used to obscure the most frequent characters, break up common bigrams etc.
- Existed before the 15th century (?)
- Effects: larger glyph set, increased entropy (sometimes or always?)
3) Homophonic cipher
- Each plaintext letter can be replaced by multiple ciphertext symbols. Hides frequency -> harder to crack
- Existed before the 15th century (?)
- Effects: larger glyph set; I would expect higher entropy but I'm not sure.
4) Polyalphabetic, "Alberti" cipher
- Allows the encoder to shift to a different substitution alphabet within the same cipher.
- Leon Battista Alberti, 1466 (-> significantly later than Voynich MS). Existed earlier e.g. in Arab sources.
- Effects: glyph set may remain the same; any textual patterns are obscured.
5) Steganography
- Any method where the actual information is hidden within less suspicious data. Hard to rule out: the only limit is your imagination. Note: the Voynich manuscript appears encoded or "secret" throughout, so it would be an edge case of steganography to begin with if any actual info is concealed in what already looks like a ciphertext.
RE: Historical ciphers, when they were introduced and their effect - Koen G - 20-05-2025
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- scrambles the positions of characters without changing the characters themselves. The changes in position are regular (e.g. each glyph in the second and fourth column is moved one line down).
- known since antiquity (You are not allowed to view links. Register or Login to view.).
- Effects: remains vulnerable to frequency analysis of individual letters; patterns may be broken up, which may increase conditional entropy.
RE: Historical ciphers, when they were introduced and their effect - Koen G - 20-05-2025
Conclusion: all known ciphers that have actually been used before the late 15th century make the plaintext even less like Voynichese than would be the case with simple substitution. Any proposed cipher methods that do produce Voynichese-like properties are therefore hypothetical.
RE: Historical ciphers, when they were introduced and their effect - tikonen - 20-05-2025
I have been thinking that there is a possibility that a variant of "Alberti" style cipher was used that could produce Voynichese-like poperties. Or a similiar method was used to produce nonsense assuming VM is a hoax.
Overview of the method:
First all the spaces are ignored in the plaintext as is often a common practice.
1. A word length is chosen by random means
2. Length defines what encoding table to use
3. Each plaintext letter (and maybe some bigrams) are mapped to a VM character or a sequence of characters (with sometimes multiple alternatives) until the target length is satisfied. Some sequences may also contain a space so they can be used only on start or end of the word. For example " qo" and "dy ".
4. Goto to 1.
This might explain some VM properties
- Binomial distribution of word lengths
- Trailing characters at end of lines when plaintext runs out but length has to be satisfied because decoding depends on it.
- Repeating words
- Preferred location in word for many character sequences
In real life this encoding would be tedious to write and decode though. It would be also very verbose so plaintext would probably be only half of the cipher text.
RE: Historical ciphers, when they were introduced and their effect - R. Sale - 20-05-2025
7) Idiosyncratic cipher
If there is meaning in the VMs text, then it is buried more deeply than the previous options.
How is an idiosyncratic cipher found? It cannot be imposed by the investigator. It must be discovered. It must be organic and innate to the VMs.
The 4 x 17 symbol sequence should be an area of greater interest. With three superimposed numeric / alphanumeric systems* visually and structurally represented in the initial part of the sequence, surely this cannot be an irrelevant artifact of chance.
* Latin numeric, medieval numeric and Greek alphanumeric systems
RE: Historical ciphers, when they were introduced and their effect - Mark Knowles - 20-05-2025
2) Introduce nulls.
Existed before the 15th century (?)
Yes. We can see the use of nulls in Gabriel De Lavinde's cipher ledger for Antipope Clement VII from 1379. Whether they were used in Europe before the 14th century I do not know.
RE: Historical ciphers, when they were introduced and their effect - Mark Knowles - 20-05-2025
3) Homophonic cipher
Existed before the 15th century (?)
I know of a homophonic cipher from 1397 in "The Chronicles of Lucca" by Giovanni Sercambi. This book available online contains a Milanese cipher that was intercepted and deciphered. However, the homophones are only on the vowels. Homophones appear to be a late(?) 14th century innovation in Europe though it is hard to be sure.
RE: Historical ciphers, when they were introduced and their effect - Mark Knowles - 20-05-2025
You mention "1) Simple substitution."
However you don't mention "Complex substitution".
This can come in different types in the period we are talking about.
In general a sequence of letters of the plaintext can correspond to a symbol of the ciphertext. This existed before the 15th century in so far as in some cases whole words were substituted with a given symbol.(See "Un Cifrario Segreto Pisano Nella Sardegna Del Trecento" by Luisa D’Arienzo)
In the early 15th century we see examples where pairs of letters or syllables or longer subsequences of letters were substituted with a given symbol.(or even substituted with roman numerals)
RE: Historical ciphers, when they were introduced and their effect - Koen G - 20-05-2025
Some things are still missing from the list. There's also the matter of nomenclatures, codes and whatever they may imply. Or to what extent any example exists that affects the stats.
RE: Historical ciphers, when they were introduced and their effect - Rafal - 20-05-2025
I would add following information
- a variant of substitution cipher is nomenclator cipher. A nomenclator is a list of codewords for commonly used names, locations, phrases, etc. I have never seen a cipher that would be 100% codewords but mixing regular substitution with codewords was common. Such ciphers usually had many different symbols so what we have in VM is rather something different
- another trick in substitution ciphers are single signs coding syllables/groups of letters
- it can be also the opposite way, a substitution cipher may be "verbose" and I mean here that several symbols are coding a single letter. We have a well known example of such cipher, known since antiquity Polybius Square:
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See also: You are not allowed to view links. Register or Login to view.
- in advanced substitution ciphers there may be many other tricks like "a sign which means to ignore the previous sign" or so. But they are probably younger than Voynich Manuscript