P1030680 - Unbroken Enigma message (U534 - 01. May 1945)
Message P1030680ENIGMA M4 MESSAGE (Nachricht P1030680):
Wheel positions: ?
Message indicator groups: VROL NMKA
Ciphertext (without indicator groups):
Note 1: Probably Key M-Thetis
Note 2: The Enigma@Home project tries to decrypt the message. You can help them with your CPU power!
Dan Girards analysis of the P1030680 M-Thetis message form:
I've been taking a close look at the Schlüsselzettel for the Thetis message. I think this is what happened:
KBuch Trigram ACH (645)Since the first bigram of the repetition of the indicator groups at the end of the message (VA) is different from the one at the beginning of the message (VR), the operator decides to try both, starting with "VA". Using the "Quelle" bigram table 'A', the bigram "VA" deciphers to "KO", which he notes on the cipher form next to the indicators at the end of the message; and the whole decipherment of the indicators becomes "KACH OEDM", which he writes in the first two rows of the "Buchgruppen" column. Looking up the trigram "ACH" in the Kenngruppenbuch, he finds that it is in row 14 of its column, and writes this number on the form; similarly, he looks up "OED" and writes its row number (5, I think) below the '14'. Next, he consults his table of Grund settings and notes the 4-letter Grund listed in column 14 row 5, and sets the Enigma wheels to this setting.
(The whole procedure is explained here: Link)
Key allocation list ACH 645 is M-ThetisAt this point, however, he forgets to check his Zuteilungsliste to find out which key-net the Schlüsselkenngruppe "ACH" is assigned to, and assumes that it is "Potsdam". He deciphers the Verfahrenkenngruppe "OEDM" with the Potsdam settings for 1 May and the Grund that he has found, and obtains "ELKC" as a message key; but when he attempts to decipher the first few letters of the message with this, he gets gibberish instead of plaintext. He then erases this, strikes out the "ELKC" that he has written at the top of the form, and starts over.
He now deciphers "VR" with the bigram table, obtaining "ES", and replaces the 'K' and 'O' in the deciphered indicator groups in the Buchgruppen" column with these letters, making them now read "EACH SEDM". He looks up the trigram "SED" in the K-Buch, finds that it is in row 9 of its column, and writes this number on the message form, overwriting the '5' that he had previously written under the '14'. Checking the Grund table again, he finds a different Grund setting in column 14 row 9, and sets the Enigma wheels to this new Grund.
Still thinking that the message is in the "Potsdam" key, he deciphers the new Verfahrenkenngruppe "SEDM" with the new Grund and obtains "PUYY" as a message key, which he writes in the right-hand column of the form; but when he uses it to decipher the first six letters of the message, he gets "IPZAYK" -- gibberish again. It's now that he remembers to check the Zuteilungsliste and finds that the column in the K-Buch containing the trigram "ACH" is assigned to "Thetis". He writes "M-Thetis" in the right-hand column of the message form, and then, presumably because the boat does not have the "Thetis" key on board, he stops trying to decipher the message.|
Although unfortunately the actual Grund tables used by the German Navy do not appear to exist any longer, it is possible to recover the Grund settings that will decipher a particular four-letter group to produce a particular four-letter message key, by means of a software program designed tor this purpose (so long as the wheel order, ring settings, and plugboard connections are known). Using such a program, the only Grund I've been able to find that deciphers "OEDM" to "ELKC" with the "Potsdam" settings for 1 May 1945 is "MNNS", and the only Grund that deciphers "SEDM" to "PUYY" is "DGUG".