CIPHER MACHINES AND CRYPTOLOGY
Stefan Krah's M4 Project and the Story of U-264
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The Project

The M4 Project is an effort by Stefan Krah to break 3 original Kriegsmarine messages, enciphered on the notorious four-rotor Enigma M4. This project attempts to break these Naval messages with the help of distributed computing, a large number of computers, working together in a network. Stefan has already succeeded in breaking 2 of the 3 messages. Meanwhile, a few thousand people have downloaded his software to help with the breaking project.

The messages were intercepted by the British destroyer HMS Hurricane in the North Atlantic on 25 november 1942. This was during the ten months black-out which occured after the introduction of the notorious four-rotor Enigma. During that period, the codebreakers in Bletchley Park were unable to decrypt the Kriegsmarine radio traffic, encrypted with the Triton keys on the new Enigma M4. More about Triton on Enigma and the U-boat War. The messages, believed to be unbroken until today, were published by Ralph Erskine in a letter to Cryptologia. On this page, we will explain the original message and guide you through the deciphering. You can even decrypt the message yourself with the Enigma simulator! Next, we bring you the story of Kapitänleutnant Hartwig Looks and his U-264. A real thriller that makes the movie 'Das Boot' look like a holiday trip!

The message

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 huge 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.

Although the first message was broken in less than two weeks, we should not forget the enormous computer resources, available to Stefan, thanks to the distributed computing. With this in mind, we must respect the incredible work of the code breakers during the Second World War who, with far less technology, still managed to break into the German communication. At the end of the war, with the combined help of more than 7000 employees in Bletchley Park, and many electromechanical devices, called Bombes, Allied Forces were able to break into the Kriegsmarine message traffic within 24 hours! Of course, the BP codebreakers didn't have the technology to perform any Brute Force attack. Instead, they used Signal Intelligence, cryptanalysis and cribs, pieces of plain text, guessed by traffic analysis, to reduce the key settings, before feeding the messages to their Bombes. It is estimated that the war was shortened by 2 to 3 years, and uncountable lives were saved by this tremendous achievement.

Courtesy of Stefan, we will show the first message break and the recovered settings. Those who want to go 65 years back in time and decipher the original message can use my Enigma Simulator, which is a great way of verifying the message.

The original cipher text, stripped of message indicator groups FCLC and QRKN that preceded the message and were repeated at the end:



 NCZW VUSX PNYM INHZ XMQX 
 SFWX WLKJ AHSH NMCO CCAK
 UQPM KCSM HKSE INJU SBLK
 IOSX CKUB HMLL XCSJ USRR
 DVKO HULX WCCB GVLI YXEO
 AHXR HKKF VDRE WEZL XOBA
 FGYU JQUK GRTV UKAM EURB
 VEKS UHHV OYHA BCJW MAKL
 FKLM YFVN RIZR VVRT KOFD
 ANJM OLBG FFLE OPRG TFLV
 RHOW OPBE KVWM UQFM PWPA
 RMFH AGKX IIBG

The recovered Settings

Enigma model: Kriegsmarine M4
Reflector: B
Rotors: Beta - II - IV - I
Stecker: AT BL DF GJ HM NW OP QY RZ VX
Ringsettings: A-A-A-V
Rotor startposition: V-J-N-A

Be sure to adjust all these settings on the Enigma Simulator before deciphering the message! After adjusting the internal and plugboard settings, set the rotors to the startposition VJNA, and start deciphering. You can use the keyboard or machine key buttons, or copy the ciphertext into the Auto-typing window (menu or F6) of the simulator. The result can be viewed and formatted with the Enigma Clipboard (menu or F5). Success with breaking your first authentic Kriegsmarine U-boat message!

The plain message

This is a spoiler!

If you want to break this Kriegsmarine message yourself, don't proceed reading before you have deciphered the ciphertext.

The message after deciphering on the Enigma:



 VONV ONJL OOKS JHFF TTTE 
 INSE INSD REIZ WOYY QNNS
 NEUN INHA LTXX BEIA NGRI
 FFUN TERW ASSE RGED RUEC
 KTYW ABOS XLET ZTER GEGN
 ERST ANDN ULAC HTDR EINU
 LUHR MARQ UANT ONJO TANE
 UNAC HTSE YHSD REIY ZWOZ
 WONU LGRA DYAC HTSM YSTO
 SSEN ACHX EKNS VIER MBFA
 ELLT YNNN NNNO OOVI ERYS
 ICHT EINS NULL

The plain text rearranged:



 VON VON JLOOKSJ HFFTTT EINS EINS DREI ZWO YY QNNS NEUN   
 INHALT XX BEI ANGRIFF UNTER WASSER GEDRUECKT Y WABOS X
 LETZTER GEGNERSTAND NUL ACHT DREI NUL UHR
 MARQU ANTON JOTA NEUN ACHT SEYHS DREI Y ZWO ZWO NUL GRAD Y ACHT SM Y STOSSE NACH X  
 EKNS VIER MB FAELLT Y NNN NNN OOO VIER Y SICHT EINS NULL

After converting abbreviations, spelled numbers and so on, the message appears:



 Von Looks: Funktelegramm 1132/19
 Inhalt:
 Bei Angriff unter Wasser gedrueckt, Wasserbomben.  
 Letzter Gegnerstandort 08:30 Uhr,
 Marine Quadrat AJ 9863, 220 Grad, 8 Seemeilen, stosse nach.
 14 Millibar faellt, NNO 4, Sicht 10.

Translated into English:



 From Looks: Radio signal 1132/19
 Contents:
 Forced to submerge during attack, depth charges.
 Last enemy location 08:30h, 
 Naval Grid AJ 9863, 220 degrees, 8 nautical miles, (I am) following (the enemy). 
 (Barometer) 1014 Millibar (tendency) falling, North North East 4, visibility 10.

The U-boat

Who is Looks, and where did the message came from? I did some research and discovered the amazing history of Looks and his U-boat. The archives show us that the message is written by Kapitänleutnant Hartwig Looks, born on June 27, 1917 in Flensburg. At age 25 he took command of U-264, a type VIIC boat laid in Bremen in 1941. The message was probably sent by one of the radio operators, Funkobergefreiter Hans Ewald, Funkobergefreiter Otto Karsten or Oberfunkmeister Ulrich Reimund, on their first patrol.

Between November 1942 and February 1944 U-264 sailed out on six patrols. U-264 operated from the U-boat harbor in St-Nazaire, France. On its first patrol, U-264 sank the Greek 'Mount Taurus' in convoy ONS-144. On its second and third patrol the U-boat came under attack from aircraft fire several times without any damage. On the third patrol U-264 sank the British 'Harperley' and the American 'West Maximus', both in convoy ONS-5.

On February 5, 1944, U-264 left St-Nazaire for its seventh and fatal patrol. U-264 was one of 20 U-boats ordered to sweep area 48°30'N-21°30'W in search of a reported convoy. U-264 arrived at the location in the North Atlantic on February 18th. U-boat command ordered it to submerge during daytime and surface after 18.00h to search for the convoy. At 09.00h, propeller noise was heard and ASDIC sonar located the U-boat. Depth charges were dropped but U-264 only took very little damage. The attacking boat left to the south-west. U-264 surfaced as ordered at 18.00h and mounted the FLAK anti aircraft gun. Ten minutes later, a Sunderland aircraft was spotted and U-264 returned fire with the FLAK gun. The first burst of fire was fatal and another U-boat reported that the aircraft crashed into the ocean.

The next morning, February 19th at 02.00h, U-264 spotted two enemy destroyers and reported this by radio with a short signal message. U-264, still surfaced, was detected by the destroyers radar and received artillery fire. U-264 managed to get away at high speed. At 04.00h they received a message that the convoy was located and U-264 sailed at high speed to the presumed location. At 05.30h, still very dark, a destroyer headed at high speed towards U-264. At 2000 meters U-264 fired a torpedo, missing the destroyer, and sped away from the enemy. At that moment, U-264 spotted the convoy and reported this with a short signal message. At 800 meters the destroyer opened fire at the U-boat and hit the U-boat's diving tanks. The U-boat's hull was not damaged and the order was given to dive immediately. The destroyer dropped several depth charges and stayed on the spot until 06.00h, when she was joined by five other ships that protected convoy ON-224. The five Sloops were HMS Woodpecker, HMS Starling, HMS Kite, HMS Wren and HMS Wild Goose, all specialized in destroying U-boats.

U-264 took many series of a new type of depth charges, the Mine-Depth-Charges, which detonated at 300 meters instead of the usual 120 meters, hitting the U-boat bottom with devastating shockwaves from beneath. U-264 sustained heavy damage. At 13.00h, the destroyers lost track of U-264, but found her again at 18.00h because of a wide oil trace, left behind by U-264 on the surface. 24 more depth charges were dropped on U-264. Since early that morning, 250 depth charges were dropped near the U-264!

Meanwhile at U-264, all electronics were lost and many water leaks were reported. The main pumps could not keep up with the raising water and a bent port side propeller axle caused the port side electric motor to overheat and caught fire. The starboard propeller was jammed completely. U-264 was out of control and sank to a depth of 230 meter. Kapitänleutnant Hartwig Looks gave the order to blow the air tanks and surface.

As they surfaced, the five sloops were in a circle of 3000 meter and immediately opened fire .U-264 could not return fire or use any torpedo since the torpedo hatches were jammed. Kapitänleutnant Looks gave the order to leave the boat. With the port side engine still rotating the U-boat, still under artillery fire, put more and more distance between itself and the men in the water. U-264 sank in the early evening of February 19th at position 48°31'N-22°05'W. Looks and all crew members, 52 men in total, were picked up by HMS Woodpecker. There were no casualties and only two sailors had minor injuries.

The crew of U-264 survived their incredible nightmare of depth charges and spent the rest of the war as prisoners, unlike many other U-boats crews. An estimated 700 German U-boats and 30,000 crew men were lost at sea.

The M4 Project Website

I would like to express my gratitude to Stefan Krah for the permission to use the first message as an example in this article. More information on the M4 Message Breaking Project and the original messages can be found on Stefan Krah's Website. On his site you can see the server logs and download the software to help him break the last message. You can also subscribe to Stefan's mailing list. If you want to use the contents of this article, please contact Stefan Krah for his permission.

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