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From: Richard Heathfield <rjh@cpax.org.uk>
Newsgroups: sci.crypt
Subject: Re: Seriation
Date: Tue, 4 Feb 2025 06:10:59 +0000
Organization: Fix this later
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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
Sig line 4 vacant - apply within