Path: ...!feeds.phibee-telecom.net!3.eu.feeder.erje.net!feeder.erje.net!newsfeed.bofh.team!paganini.bofh.team!not-for-mail
From: Stefan Claas <pollux@tilde.club>
Newsgroups: sci.crypt
Subject: Re: Seriation
Date: Sun, 8 Dec 2024 20:52:54 +0100
Organization: To protect and to server
Message-ID: <vj4tf6$g0ta$1@paganini.bofh.team>
References: <vj1pgp$5u55$1@paganini.bofh.team> <vj4o37$3uq6p$1@dont-email.me>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=fixed
Content-Transfer-Encoding: 8bit
Injection-Date: Sun, 8 Dec 2024 19:53:10 -0000 (UTC)
Injection-Info: paganini.bofh.team; logging-data="525226"; posting-host="5dN2j+dHj3x3pXnD1olf1w.user.paganini.bofh.team"; mail-complaints-to="usenet@bofh.team"; posting-account="9dIQLXBM7WM9KzA+yjdR4A";
User-Agent: flnews/1.3.0pre21 (for GNU/Linux)
Cancel-Lock: sha1:cY3ESyOIasch3u1aZjCv2O+hSik=
X-Date: It's Sun Sep 11422 08:52:54 PM CET 1993, the September that never ends.
X-Ed25519-Pub: c0ffee5a36e581eb10f60b2831b3cdb955d2e7ef680dd282a8d43ad8b84b357a
X-Notice: Filtered by postfilter v. 0.9.3
X-Ed25519-Sig: fff9f4378f9ca60d6319863a09ce9f565226f4bc3569fadbfda7a991a6088d79
 084e795838e28e84b4e82684128efc06000a82d468e116a92b21a07b3ead550d
Bytes: 3434
Lines: 53

Peter Fairbrother wrote:
> On 07/12/2024 15:27, Stefan Claas wrote:
> 
> > Seriation was used in the German WWII cipher Doppelkastenschlüssel
> > and I thought it is pretty cool. However, I did not managed yet to
> > understand how encryption and decryption works.
> 
> Doppelkastenschlüssel was a hand cipher of the type known as double
> Playfair, or horizontal two square, used by the German Army throughout
> WW2 as a field cipher.
> 
> It works pretty much like Playfair except there are two 5x5 Polybius
> squares; the first letter of a plaintext digraph goes in the left square
> and the second letter goes in the right square. As in Playfair, the
> opposite corners of the rectangle form the ciphertext, with the letter
> from the right hand box first.
> 
> If both letters were on the same horizontal line the previous letters in
> the line were used, also usually with the letter from the right hand box
> first.
> 
> The squares were random, not based on keywords (so they seldom ended
> XYZ), and were distributed using a key network.
> 
> 21-letter (usually) seriation was used to make both digraph frequency
> analysis and transparency analysis harder.

According to the German WWII documentaion 17-letters per two lines,
a blank line and then again 17-letters per two lines and so on.
> 
> Cascaded substitution, where the results of the digraph substitution
> were used as inputs to a second substitution, was also used (sometimes).
> 
> It was broken by both US and UK cryptanalysts:
> 
> media.defense.gov/2021/Jun/29/2002751757/-1/-1/0/WORLD_WAR_II.PDF
> 
> 
> A similar two-square cypher was also used by the Germans later in WW1,
> but based on keywords and without seriation.

Thanks for the info. I have read the following German docs, one original
from WWII[1] and the Wikipedia[2] article.

[1] <https://cryptocellar.org/wmc/schluesselanleitung-dk-1940.pdf>
[2] <https://de.wikipedia.org/wiki/Doppelkastenschl%C3%BCssel>

Interesting also Klaus Schmeh's articles on this subject.

<https://scienceblogs.de/klausis-krypto-kolumne/tag/doppelkasten-schluessel/>

-- 
Regards
Stefan