Re: Seriation

On 04/02/2025 01:31, David Entwistle wrote:

On Mon, 3 Feb 2025 10:17:24 +0000, Richard Heathfield wrote:
 

#define UPPER "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
#define LOWER "abcdefghijklmnopqrstuvwxyz"
#define DIGIT "0123456789"
#define PUNCT "!\"$%^&*()_-+={}[]#~'@;:/?.>,<\|"
>
which isn't particularly wide, but any encryption of any of those
characters will *always* produce a character drawn from the same set.
When faced with something *not* from that set, SCOS leaves it unchanged.
So I think I'm right in saying that by the above definition SCOS /is/
closed.

 Yes, as I recall, and as a rather sloppy adversary unaware of your
implementation, my character set ran from char(33) ! to char(126) ~. I
think it was the gap between char(95) _ and char(97) a which caused me the
most trouble. char(96) is top left on a QWERTY keyboard. I never use it,
but it gets used as an apostrophe in some text on the web. As a result
some of my checks failed to do what I expected and I didn't feel confident
posting SCOS-based ciphers.

Well, blow moi down with a feather! I had no idea! The backtick does indeed fall by the wayside... and I *do* use it a lot --- as `` for "open speech marks" and \` (grave accent) in LaTeX --- so I really ought to have remembered it, but it turns out I did overlook it.
And *that* means that if I use my completely insecure program to encode a LaTeX document for posting on the Net with the express intent of allowing a few people I've never met to crack the ciphertext, as well as having an easy task they'll have the additional benefit of having the backticks pre-cracked for them.
In the real world it would of course be an embarrassing screw-up that hopefully would be caught by a proper test plan. In the rarified atmosphere of sci.crypt, however, I can afford to be sanguine.
It now occurs to me that I could remove other characters to have them left treated untreated. For example, the following ciphertext is the (key 31 41) output from a SCOS2 variant (with just one line of code changed) that passes through everything but alphabetical characters:
Byuj, ONFC hYH rroU SttW E ymXfIuw! C Qyq pf OyoZ! HKw iWNKImVS AAfi NHmcRF wggV AM wZL SlyhMwm... XZE Y *ii* dQr kk G Gys --- OV `` xvn "ZPtr lXBqdX RuAif" CEj \` (bbzJh SJypni) MG TXFFn --- xi r PrccRT ytUKL Ak SAKi kMJqnRJLnb VV, sAo SS HxjUO zui m wqa aWuwfXMx kk.
gIn *sVDL* taLNH xaIQ ug y ZMn kl EFskVDHhdf EysTGNzb bSEllJK Gq VTxycS D dhPPx ssVcJqoj KIA nbUKoiQ NB wZL jpt lMMp qTF uCjaCFu ZTOomh Rx hhWOLmgO x rfm UyxnYG Z'BZ XDJhj TAE td GKiZW Uxj WRNugiZzHs, OV OlhW AH lTdFzh QS yjql Vryf dGsB'dS DlvT XAm XPEyycXLnn SKIoeWW Gm dLVxrZ bEq cQHECgPMJ vmO-BFdURAo fdV MpbY.
jD ybN Prcc cJBkR LL DkfLs sY KLGsiJ vn Ya GDhVbQovkPJr sRVxE-rb Uxfn QMCgWaGvx kRMsZ ME renOEF co F JAmcGI zZcS DoSU. ey tWI KioUGyjX JRzqjVCoqS Rx zYT.CGCib, EAxUayA, G PCE gaPNFg lV xp sPRzCfZF.
Yy hXU BeTaMC sc Pw AdLT X ghcIp sURIEc bVykm MGouSJPprh XH pXhF JmYV Jrhk ZMoZhHv BjeRtemMA. Rph JRjkcNv, zcO ECodVStnV GBxeQSJjrc GF vYK (Fox 31 41) cXLwqe FGsf I pOPI2 auAgNPK (CddG xxka Kye aMGm lR DEiY LFnpXKy) DgOW HhodEH xaZLGhX JPnplVyoiQ AIw SSLsaQIMqZMM smUaypvVXN:
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
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