Are there any publications, articles or literature discussing cryptanalysis and crypt breaking techniques in the middle-ages?
I have seen various manuals from the middle ages describing various types of encryption, also mentioning that Caesar substitution cipher can be easily broken, but I cannot find any information on algorithms and knowledge they used to do so.
Update:
I've found first description of substitution cipher breaking called unfolding at John Wilkins (1641) Mercury: Or the Secret and Swift Messenger, page 88 and further, chapter XI.: The General rules of unfolding ..., available online: https://archive.org/stream/gu_mercuryorthes00wilk#page/n111