Tuesday, February 21, 2006

M4 Message Breaking successful

Stefan Krah succeeded in breaking the first of 3 original Enigma Kriegsmarine M4 messages. The M4 Project attemps to break these 3 Naval messages with the help of distributed computing. The messages, believed to be unbroken until today, were intercepted in the North Atlantic in 1942.

The encrypted messages were published by Ralph Erskine in a letter to Cryptologia. You can find Ralph 's original messages here. To perform the ciphertext-only attack, Krah used a combination of brute force and the hill-climbing algorithm. The program runs through all possible settings of the Enigma, except the plugboard. The plugboard settings are a huge portion of the key space. Omitting them during the attack saves a hugh amount of time. For each machine setting, the hill climbing algorithm is used to optimize the plugboard settings. The algorithm tries to optimize the plugboard settings, by changing the plugboard, step by step. After each step, the 'quality' of the result is determined by a scoring function. If the score is better, the change is retained.

Yesterday, this approach resulted in a first successful break into a Naval message. On this page, you can read the broken message. You can use my Enigma Simulator to verify the results by using Stefan's recovered machine settings and decipher the message yourself.


Stu Savory said...

I would parse the plain text slightly differently :

In the Header: KS=Kapitän zur See (a rank).

In the progress report :
"stossen nach" should be translated as "We are following", IMHO.

In the Weather report :
NO = Nord Ost (=north east)
and 4 mb not 14 mb (meaning 1004 mb).

Frode Weierud said...

No, the header is correct. Rank was usually not given. The "Von Von Looks" is in reality the signature.

The progress report should be "Stosse nach" instead of "Stossen nach", but Stu's translation is correct.

In the weather report the wind direction and strength should be "NNO 4" - Nord/Nord Ost force 4, while the pressure report is correct as "14 mb faellt", which is a pressure difference type of reporting. This all correlate with information given in Wetterkurzschlüssel (3. Auflage), Berlin 1942, M.Dv. Nr. 443.

It happens that a Naval historian has discovered exactly this message in a war diary which is on microfilm in the American National Archives, NARA. Here is the archive text:

1930 Funkspruch 1851/18/252:
F T 1132/19 Inhalt:
Bei Angriff unter Wasser gedrückt.
Wabos. Letzter Gegnerstand 0830 Uhr
AJ 9863, 220 Grad, 8 sm. Stosse nach.
14 mb. fällt, NNO 4, Sicht 10.

And if anybody wonder who's Looks it is (pun intended), it is:
Kapitänleutnant Hartwig Looks commander of U-264.


Dirk said...

You can check out the U-boat commanders on U-boat net:


His U264 sunk in feb '44 by depth charges. Surfaced, all 52 survived. Details on U264 here:


Even more details here:


Dirk said...

Story of U264 sinking:


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