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I stumbled upon an encrypted text on a website, to which Google had brought me, showing me the plain text also. So does anyone know what kind of encryption was used here and how to decrypt it, so I can decrypt the rest of the text?

Encrypted text:

Deälldllod Lokl Koih, dg emlll ld kmd Llshlloosdelädhkhoa Lühhoslo ha Melhi hlhmoolslslhlo, dgiill kll shllll Hmomhdmeohll kld M8-Modhmod

Plain text:

Spätestens Ende Juli, so hatte es das Regierungspräsidium Tübingen im April bekanntgegeben, sollte der vierte Bauabschnitt des A8-Ausbaus

First it looked to me like a substitution cipher, but there are multiple letters which translate to l. So is this a substitution cipher, where no decryption is possible, or is there an other way?

I look forward to your suggestions.

Patriot
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Kaniee
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2 Answers2

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Well, it seems it is a basic substitution cipher, with a twist: some letters map to the same cipher text letter (not just e,r,t map to l, also e.g. n,u map to o . So decryption is not unique. But a pattern matching algorithm with a German dictionary could probably filter those. The mapping seems to group letters in such a way, that only one combination makes sense.

Anyway, from the example text you can probably find most character mappings, and then you just need to guess words based on valid combinations in a dictionary.

In general, I would not actually call this encryption at all. A scheme like this won't work for just any non-injective mapping, so it's unclear if there is some key involved or not. Also, an encryption scheme requires, that (with overwhelming probability) the decryption is unique and correct, s.t. $D(E(m))=m$.

tylo
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  • You are probably right, that this is a non-injective mapping. I hoped, that there is popular mapping method, which would explain this cipher text. Decrypting it with a dictionary is a good idea but is to complex, since there are 4^4 * 2^2 possible combinations just for the word "Deälldllod". – Kaniee Aug 29 '19 at 19:49
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    @Kaniee: Regular expressions can be your friend here. On a Unix box with a suitable word list installed, grep -wi 's[hp]ä[ert][ert]s[ert][ert][nu]s' /usr/share/dict/german should spit out the answer in no time. (And a custom program could be orders of magnitude faster yet, at least when decrypting multiple words.) – Ilmari Karonen Aug 29 '19 at 22:39
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Yes is it a substitution cipher. But it seems to have very strange rules. Which are not totally clear to me also.

Most of it is straightforward, o=u, m=a, h=i... But as you said correctly. ll=re, te, tt. There might be an explanation that lll is treated different, as lll= tte and llll=erte. But that is not verifiable in this short example.

Also that does not solve the difference between Bauabschnitt (tt=>ll) and der (er=>ll) There is something strange and non-deterministic going on. Either there is a rule about the length of the words or something.

There is also an bi => hh in Tübingen. Which does not make sense. I don't know the source, but i suspect there is either a very random logic behind it or there was an error.

oicrisah
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Sango
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