Re: VMs: RE: GC's first reply

[Gordon Rugg <g.rugg@xxxxxxxxxxxxxx>]

Dear Nick and all,

As Nick points out, knowledge of some statistical issues relating to cryptology
was explicitly available in the relevant period. A hoaxer, or someone wishing to
conceal a code, could use that knowledge to mislead or confuse would-be
decipherers.

There's also the separate  issue of statistical properties such as entropy values
which were not known until much more recently. These could not have been
deliberately included as part of a hoax before they were discovered, as Gabriel
points out; my point was that they may have been accidentally included, as
by-products either of a hoaxing method or of a coding method. For instance, the
Beale ciphers show a tendency to favour numbers which are directly divisible by 5,
which can plausibly be explained as a by-product of the system used to number the
words of the Declaration of Independence.

Best wishes,

Gordon

Nick Pelling wrote:

> 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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