Re: Seriation

Welcome back, after a long silence.

Richard Heathfield <rjh@cpax.org.uk> wrote:

On 08/12/2024 05:58, Rich wrote:

Stefan Claas <pollux@tilde.club> wrote:

Peter Fairbrother wrote:

Seriation is not a cipher, it is a technique used to build ciphers. Like
substitution and permutation, of which it is a form of the latter.
>
It can be useful eg with digram-based ciphers like Playfair, where it
makes cryptanalysis based on the known frequency of occurrence of
digrams in the plaintext language much harder or impossible.

>
Yes, thank you for the explanation! It could also be a nice replacement
for SCOS, here in sci.crypt, combined with an A-Z encoder/decoder and a
padding program, since SCOS was cracked and floating around on Bitmessage
and code for seriation I have not seen yet elsewhere.

 
SCOS was never meant to be in any way 'secure'.  Hense the name: (S)ci
(C)rypt (O)pen (S)ecret.  It was meant as a fun exercise at
cryptanalysis and working out a crypt/decrypt algorithm given examples
of encrypted messages.

 
I think that's almost, but not quite, 100% correct.

What I posted was what I took to be the meaning from your posts. 
Naturally I may have 'diverged' slightly in my interpretation from your
true intent (my not having a Usenet crystal ball with which to read
minds remotely certianly helps explain some divergence).

If I recall correctly (and it's entirely possible that I don't), what
I was after in SCOS was something just a little bit harder to read
than ROT-13, because people here were having ROT-13 conversations
that they clearly believed some regulars (eg aob) couldn't read, but
I couldn't quite bring myself to believe that anyone could be
incapable of decrypting ROT-13.

I do believe there were some rot-13 posts, and quite possibly an
assumption that AOB could not crack them.

But that was AOB we were dealing with.  His knowledge of actual
cryptography was very much suspect, so it is 'possible' he could not
crack them himself.  Now, might he have found a rot-13 decryptor web
page to use, possibly.....

The point of SCOS was a little like the point of the scary devil
monastery.  If you could post in asr, it proved you were good enough
to post in asr, and if you could post and decrypt SCOS messages it
proved...  well, that you were good enough to take part in SCOS
conversations.

Ah, so maybe I did miss a sublety in your intent -- beyond a "christmas
holiday fun exercise in decrypting a new system".

But yes, being easy (but not /quite/ trivial) to crack was indeed at
the heart of SCOS.

Do note that by "secure" I was referring to Claus' usual statements
about being able to communicate from "inside enemy lines in a hostile
environment".  I doubt very much you'd recommend SCOS or SCOS2 for such
usage.  I certianly would not recommend use of either variant for a
"behind enemy lines" or "hostile environment" situation.