In 1941, a sender in Hamburg, Germany, transmitted an encrypted message to a receiver in Rio de Janeiro, Brazil. The encryption method and the key are known, but the plaintext has not been completely deciphered yet.

Ralph Erskine, an Enigma and crypto history expert from Northern Ireland, …

Source: Erskine (used with permission)

… has made me aware of an interesting document: a report from WW2 US Coast Guard Unit 387 about German cipher systems.

Coast Guard Unit (CGU) 387 had its origin in a codebreaking group that solved rum smuggler codes during the Prohibition, with Elizebeth Friedman (the wife of William Friedman) being the most famous member. Later, CGU 387 intercepted messages between Latin America and Germany, which became especially important when the USA entered the war against the Germans. The unit’s greatest success was the breaking of messages encrypted with a special German Enigma variant (Abwehr-Enigma), based on information received from British cryptologists in Bletchley Park.

According to the report, CGU 387 intercepted a considerable number of German radio messages. Apparently, they solved many of them. As it seems, most of the encryption systems the CGU 387 cryptanalysts encountered were not very secure. Most turned out to be manual ciphers used by German agents to communicate with their intelligence organisations. Some of the systems were based on the Rudolf Mosse Code, an international, non-secret telegraphy code.

On page 17 of the report, the following message sent in October 1941 from Hamburg, Germany, to Rio de Janeiro, Brazil, is reproduced:

This ciphertext is encrypted in a Vigenère cipher. The key is not a word, as one would expect, but the following number: 3141592. This digit sequence is derived from Pi (3.141592…). The first seven letters are decrypted as follows:

DDLUXCQ SFVINNN
3141592 3141592
---------------
ACHTSTO PERHIEL

According to the report, the CGU 387 codebreakers determined the key length by looking for repetitions (this method is also known as Kasiski examination):

It will be noted that there is a six-letter repeat DLUXCQ and a three-letter repeat (OIV), plus two two-letter repeats. There are 196 letters between the six-letter repeat and 28 letters between the three-letter repeat, both divisible by seven. Dividing the ciphertext into seven sections, taking every seventh letter, frequency count was taken …

Transcribing this message proved difficult, as some letters are hard to read. In addition, some of the characters are obviously wrong. After several corrections of my first try, here is the best version I got:

DDLUX CQSFV INNNW FRFZA GQBGI
WREKU ZPRIY HJXFS JRUJP TYXRH
SABWC GQFYD MIXYP VNJRE KNLHJ
QGQAI JYNPV USQLJ DHOIV HQXRN
HSJRU VJKTY NPPBI SEKKV OIVSC
GQBTS NUPXS FVHQU WBFFS PTXQT
FSXJQ FWJSW UWPTC JIWHH PJHQD
HUVFZ DPJBF XFAVH URBHQ TLDLU
KEQQD ESQXU

When I decrypt this message with Cryptool 2 (the key 3141592 corresponds with the letter sequence DBEBFJC), I receive:

ACHTS TOPER HIELT ENEUR ENACH
RICHT VOMZW EITEN APRIL STOPE
RWART ENEUC HZVVO RMEIC HMHGE
HENZE ITENS TOPGA BENEU CHVOM
DREIS SIGST ENMAE RZBIS NEUNT
ENAPR ILNUR BUCHS TABEN GRUPP
ENOHN ESINN STOPB EZUEG LICHB
ETREU UNGAB WARTE TNACH RICHT
FVONC ARLOS

This can be interpeted as follows (STOP means period):

Acht. Erhielten eure Nachricht vom zweiten April. Erwarten euch ZVVORMEICHMHGEHENZEITEN. Gaben euch vom dreißigsten März bis neunten April nur Buchstabengruppen ohne Sinn. Bezüglich Betreuung abwartet Nachricht F von Carlos

Here’s a translation:

Eight. Received your message from April 2. Expect you ?????. Gave you from March 30 to April 9 only letter groups without sense. With respect to support, wait for message F from Carlos

This message makes perfect sense, except for the passage ZVVORMEICHMHGEHENZEITEN. There must be a mistake in the original or in my transcription – perhaps a missing letter or a few false ones. Can a reader find out what the correct version of the plaintext is?


Further reading: Who can break the cryptograms of Civil War spy Robert Bunch?

Linkedin: https://www.linkedin.com/groups/13501820
Facebook: https://www.facebook.com/groups/763282653806483/

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Kommentare (8)

  1. #1 Thomas
    27. Juli 2019

    The missing plaintext sentence: “ERWARTEN EUCH ZU VORGESCHLAGENEN ZEITEN”

  2. #2 Armin
    27. Juli 2019

    Ich denke, es heisst:

    ZUVORGESCHLAGENENZEITEN

    Der zugehörige Geheimtext wäre dann:

    MIWYPVHJBEKMEHJWGQAIJYNP

    Die Zeichen, die man in Deiner Transkription dafür ändern müsste, würden auch durchaus zu den unleserlichen Geheimtextfragmenten passen.

  3. #3 Armin
    27. Juli 2019

    Thomas war schneller. 🙂

  4. #4 Rozaenriste
    Deutchland
    27. Juli 2019

    Great post!

  5. #5 Klaus Schmeh
    27. Juli 2019

    @Armin & Thomas:
    Thanks, this mystery is solved.

  6. #6 Klaus Schmeh
    27. Juli 2019

    There was also an error at the end of the message. Here’s the correct transcription:
    DDLUX CQSFV INNNW FRFZA GQBGI
    WREKU ZPRIY HJXFS JRUJP TYXRH
    SABWC GQFYD MIWYPVHJBEKMEHJWGQAIJYNPV USQLJ DHOIV HQXRN
    HSJRU VJKTY NPPBI SEKKV OIVSC
    GQBTS NUPXS FVHQU WBFFS PTXQT
    FSXJQ FWJSW UWPTC JIWHH PJHQD
    HUVFZ DPJBF XFAVH URBHQ TLDLU
    XCQSD ESQXU

    And here’s the correct plaintext:
    ACHT STOP ERHIELTEN EURE NACHRICHT VOM ZWEITEN APRIL STOP ERWARTEN EUCH ZU VORGESCHLAGENEN ZEITEN STOP GABEN EUCH VOM DREISSIGSTEN MAERZ BIS NEUNTEN APRIL NUR BUCHSTABENGRUPPEN OHNE SINN STOP BEZUEGLICH BETREUUNG ABWARTET NACHRICHT STOP CARLOS

  7. #7 Klaus Schmeh
    27. Juli 2019

    Nils Kopal via Facebook:
    The correct solution is in the comments of Klaus Blog. Here I created it also with CrypTool 2:

  8. #8 Sandra Schmidt
    Greifenstein
    17. August 2019

    Hallo! Persönlich denke ich, Fenn’s Ort sind die Devils Eyes im Yellowstone. Er hat den Schatz dort versenkt, deshalb nass. Die Flamme sieht beeindruckend aus. Wahnsinn….