Re: VMs: RE: GC's first reply

[Nick Pelling <incoming@xxxxxxxxxxxxxxxxx>]

Hi Gabriel,

> > As far as I can tell, we simply don't have much solid reported data about
> > how easy or difficult it is to hoax any given feature of the VMS, so
> > opinions about this are currently at the level of speculation.
>
> What we know, though, (if one assumes that the ms was written in 1400s or
> thereabouts) that a number of its statistical properties are very unlikely to
> have been planned because their existence was not apparent at that time. One
> cannot design what one does not know.

Cicco Simonetta (arguably the father of modern cryptology), in his 
(admittedly short) "Regule ad extrahendum litteras ziferatas, sine exemplo" 
of 1474, gives a systematic set of rules for breaking monoalphabetic 
ciphers. This specifically relies on an understanding of statistical 
properties!

There is also ample evidence, from looking at the evolution of ciphers 
through the Quattrocento (for example, in the Milanese cipher ledger, and 
elsewhere) that they were being broken and replaced in a crypto arms race. 
Simonetta may have been the first person to make what was formerly tacit 
knowledge into explicit knowledge - but it's quite clear that the knowledge 
was there all the same.

Also: GC commented recently about straddling the divide between code and 
language - for me, this is a really important point, as I believe that the 
kind of pair cipher employed here was constructed specifically in order to 
make it look like a monoalphabetic cipher *when viewed at the wrong 
level*... to be precise, like a language in an unknown alphabet (one might 
call this an "interior language"). So, my view is that the interior 
language's statistics were deliberately constructed to make it appear like 
a real language.

This "interior language" property of pair ciphers appears to have been 
forgotten by the time of Vigenere: the only full-on pair cipher I found 
there (the Alphabeth Northmanique) seems really superficial, barely 
misdirecting at all.

Overall, I think a cryptologist (even in the 15th Century) with a good 
feeling for the properties of language would be able to use pair ciphers to 
construct a realistic-looking interior language: and to a cryptologist, 
"realistic-looking" would (naturally) be with respect to its statistical 
properties.

FWIW, I think that our author was still just a little too reliant on "o" 
and "y", which I guess may well have skewed the interior stats probably a 
little more than what was originally intended. Though there may yet turn 
out to have been a good reason for this... perhaps we'll see later... :-o

Cheers, .....Nick Pelling..... 


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