Cryptanalysis in the middle ages -- publications 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
Holden's "The Mathematics of Secrets" has nearly comprehensive explanations with rough algorithms to follow for each of the steps. It is meticulously filled with citation and rife with references to materials for additional study. It is an excellent resource for this inquiry. A good companion for it is Singh's "The Code Book".