Re: VMs: Three frequency tables

[Nick Pelling <incoming@xxxxxxxxxxxxxxxxx>]

Hi Dennis,

At 22:39 19/12/2003 -0600, Dennis wrote:
>         But what else are you thinking of?  Do you mean that
> you don't think the gallows are just markers for cipher
> change?  (I've never liked that either, but that
> because it doesn't look like a polyalphabetic cipher to
> me.)

Perhaps we might usefully describe ciphers which change state only on 
certain characters as being "multi-cipher" (rather than "polyalphabetic", 
which we might instead use to denote those which continuously cycle / 
change on every character).

While it's entirely possible that (as Steve Ekwall suggests) the VMs is 
multi-cipher and changes cipher table on gallows (rather: that it folds on 
gallows, flips on <ch>, and rotates on <ee>), note that that doesn't 
necessarily imply that gallows could only act as "markers" (ie as 
state-change tokens with no semantic content).

For example, each gallows state could have a separate (cipher-specific) 
replacement value for each gallows character that appears after it. This is 
quite possible - but I don't feel 100% comfortable with it, as it feels too 
"fragile" for a Quattrocento cipher system. FWIW, there's a kind of mental 
step cryptography took (circa 1500) with the move to polyalphabeticity, 
whereby *robustness* was seen to be tradable for *security* - but I don't 
think this is the case with the VMs.

If instead the gallows (as per the GMT) act as proxies for letters in some 
kind of local key (whether horizontal, vertical, line-initial, line-final, 
or whatever), then they could function *both* as local replacement 
characters *and* as global state-change tokens. This would be an extremely 
interesting way of combining two simpler cipher systems into a more complex 
system - and is what I suspect is probably going on under the VMs' hood. :-)

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


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