20-05-2025, 06:29 PM
(This post was last modified: 20-05-2025, 06:32 PM by Mark Knowles.)
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)
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)