Historic cipher mapping

[pfeaster]

The concept of the Polybius square is very simple and very easily re-invented. I can imagine it being independently re-invented by the VMS creator, especially given such famous example of matrix placement of a sequence of characters as the Sator square.

I agree that it seems simple.  But many inventions seem obvious once you know about them, in hindsight, even if they weren't obvious at all before someone invented them.

On the topic of "mapping," then, it would be especially interesting to know if there's any evidence of a fractionating cipher of any kind being used (or even just speculated about) in the century or so before 1450, and if so, where and how.

One other thing it would be nice to know is the history of access to the specific part of Polybius that describes a fractionating cipher.  This passage is in a fragment of Book Ten, so people who had access to other parts of Polybius's Histories didn't necessarily have access to *that* part.  (How this affects the Leonardo Bruni connection, I'm not sure.)  The editio princeps of the Book Ten fragment(s) seems to have been You are not allowed to view links. Register or Login to view., for what it's worth: nineteen years after Books One through Five.  As for secondary references in the cryptological literature, the Polybius Square comes up in You are not allowed to view links. Register or Login to view. -- don't know offhand if there's anything earlier.  Here's how Della Porta displays it: