March 21st 2011

"Enigma now and then"

         Dr John Rant, NES Council Member.

John started his talk to a large audience of members and guests by outlining the developmental history of the enigma machine. The ability of any organisation to keep in touch with its component parts without its competitors being aware is often crucial to the success or otherwise of any of its active projects. This applies as much to the military world as the commercial world!

Indeed the military often have much larger resources available to them to develop new methods of communication. One of the problems that was troubling the navies of the world during WWI was communicating messages between their vessels using wireless telegraphy. The main problem with this method of communication is that it is relatively easy for your enemy to listen in on your signals. To keep the information secret some sort of encipherment has to be used. This has to be relatively quick and must be reliable both to encode and decode the messages but using a methodology that is extremely hard for the enemy to break if they don't have the appropriate equipment/knowledge.

Even though they were neutral during WW, one line of approach examined by the Dutch Navy, with some success, was to develop electro-mechanical coding systems using cross-wired rotors where a given pathway was associated with an input message character with the output always being a different character- a sort of electromechanical substitution coding device. By itself one wheel is not enough. What the Dutch engineers, Schebuis and Koch, realised that much more security could be obtained by using linked wheels that altered their relative positions each time a character was encoded; they adopted the simple principle that after each encodement the first wheel would move through one step.

All subsequent wheels move through one step each time a previous wheel has moved by complete revolution. Adopting this approach means that the number of substitutions before repetition rapidly increases with the number of wheels involved.

Koch also realised that the system had the property of reversibility in that if the encoded letter was passed back through the system its original unencoded character would be available; thus an identical machine with the same wheels in the same positions and starting configuration could be used as a decoding device. Hence to be able to decode your message the enemy needed to have knowledge of the wheel structure and relative positioning and the starting configuration. Though denied patents at the time Koch subsequently took out patents in 1919 in Germany. A small company in Germany, Cipher Machines Stock Corporation(CMSC), was set up to exploit these patents which they acquired in 1923. CMSC had the vision that commercial organisations, such as banks, could use this type of machine to keep their financial transaction secret from their competitors.

In 1926 they put a 3 rotor with a reflector disc on the market; the purpose of the reflector was to send the signal back through the wheels by a different route to be output as character lights on an output panel. This machine became the core of the 'Enigma machine'.

In the early 1930s, particularly after Hitler's acquisition of power in 1933, the German armed forces (OKW) started to investigate encrypting machines in earnest. They rapidly came to the conclusion that a device similar in principle to the CMSC machine would be a very useful adjunct to their communications systems particularly if they could be manufactured in quantity and a secure usage strategy could be set up.

As they believed that the encipherment using this approach was to all intents and purposes 'uncrackable' in any realistic useful military time frame, they would be more than happy to use them in a dynamic situation particularly where landline communications were non-existent or damaged and hence unreliable. Just the sort of situation some of their planners were needing in their 'Blitzkreig' type of operation.

Some of the planners were so confident in the potential security of the system that they were even envisaging that there would be no necessity to go to the trouble and cost of replacing the tactical wireless networks with landlines. This was particularly the case with the German Airforce (Luftwaffe); this proved to be a very expensive mistake!

However before they actually used the machines OKW made several important modifications such as altering the wheel rotor wiring, allowing each wheel to have alterable settings within their mounting and introducing a variable patching board at the input to the rotor system. These modifications led to a repetition rate of 1 in about 400,000,000,000,000; superficially the odds of cracking a code were well nigh 0.

They also introduced several operational rules such as changeing the wheel settings on a daily basis and which subset of rotors were to be used on a given day; the military machines had more rotor types than were needed for a given machine; 3 out of 5 for the army and airforce and 4 out of 8 for the navy. The navy had decided quite early on that their machines were to be even more secure than the other branches of OKW because on operational station their only communication channel was by wireless telegraphy.

To make the system work each machine on a given wireless net was issued with a code book informing the operatives what wheels to use in what positions and wheel settings and what pairings to use on the patchboards for the given session. In their training the operatives were also told how to test the network and what keying procedures they should follow. Given the odds mentioned above and if the operating procedures had been followed it would appear that the OKW were justified in assuming that the system was foolproof.

John spent a little time in explaining how, with lots of clever effort and bravery on the part of the allies, sloppiness on the part of the German operatives and just plain luck the system was broken into quite early on and despite several hiccoughs on the way remained broken throughout WWII.

Starting with the luck. After Hitler came to power the Poles became concerned that one of the objectives of the new regime was the reacquisition of Danzig by Germany and that the only way that they could achieve this was by invading Poland. So they put lots of effort into cracking German codes.

The luck was that the German Diplomatic Service also used Enigma like machines and all mail for their Embassy in Warsaw passed through the normal mail service albeit in diplomatic pouches. Even the new coding machines were sent to Warsaw this way. If an embassy official hadn't been too pushy in extracting the machine pouches over a weekend the Poles would have been none the wiser.

However because of the over zealousness of this official the Polish Secret Service decided to illegally tamper with the pouches. Inside one of these bags they found an early Enigma machine. The Poles rapidly put together a team of engineers, cipher experts and mathematicians examined the machine. The machine was returned to the diplomatic bag which was so expertly resealed that the embassy didn't realise that the bags had been tampered with. The polish team then started on the difficult task of decrypting the output of such a machine. By the outbreak of WWII they had made great strides in this direction. In early 1939, when it became obvious that an invasion of Poland was highly likely, they contacted their opposite numbers in the France and Great Britain who had just signed alliance agreements with Poland.

Both these countries had already begun the process of rapidly expanding their intelligence decrypting services; in the case of GB this meant building a significant number of wireless interception stations and the setting up of the Cipher School at Bletchley Park (BP). Both groups had, with the help of the Poles and informer based intelligence, started developing electromechanical systems to aid with the decoding of intercepted messages; perhaps the best known of these was Alan Turing's "Bombe". However these machines were very much assisted by the lax transmission procedures used by the German signallers who truly believed that their coding system was unbreakable. Another important flaw, which came through the Polish examination of the diplomatic machine, was designed so that no letter could be encoded as itself.

As the allies realised early on possession of an active 'procedures' book would be extremely beneficial. Through just good fortune and a lot of bravery they obtained several copies either through taking out enemy weather ships and boarding sinking U-boats or rapidly overrunning army headquarters in the desert campaign. Using all these tools and being extremely careful how the resulting intelligence ("ULTRA") was actually employed the enemy, with the notable exception of the naval arm, never became suspicious that their system was severely compromised. In the case of the Navy, because of the rapid increase in U boat sinkings, Admiral Doenitz instituted a review of the enigma generated communication. However in every sinking case an allied airplane had been observed by the targeted U boat; the report to Doenitz put the sinking down to being observed from the air not to a failure in the communication encoding process. The reality was that if a U boat's position was discovered through "ultra" an aircraft was flown to that position if at all possible.

John told his audience about one development close to the end of the war that caused a black-out in Luftwaffe "ultra"; the so called "Uhr box". This was a system that effectively replaced the patch board and made new connections literally every hour. This machine had 80 contacts of which 40 were used in any given time interval. Fortunately by this time the Luftwaffe were to intents and purposes 'down and out'.

John concluded his talk by describing a simulation of an Enigma machine on a 'build it yourself' computer. He gave an outline of what the system could do and invited members of the audience to try it out at the end of the session. A lively Q&A session then followed. After the vote of thanks many members of the audience took up John's offer of being an enigma operator and/or a BP decoder.

Richard Aldridge          April 2011