The History and Mathematics of Codes and Code Breaking

Tag: espionage

Human Error and Forced Flaws

Photo Credit: “Chiffriermaschine ‘Enigma’ ” by Walther licensed by Wikimedia Commons under Creative Commons

The Enigma Machine was practically impregnable if all of its information was kept secret and all its operators worked without human error. With billions and billions of possible settings, it would have taken cryptanalysts an obscene amount of time to sort through all of the possible keys. Additionally, with an ever changing pattern and shifting scramblers it would be incredibly hard to find a method to deduce the plaintext if all one had was pure ciphertext, even with if the most brilliant minds in Britain working on a solution. Essentially, cracking the Enigma required some sort of “crib”, some insight into how the code was working on a specific day that would take out some of the possible Enigma settings.  Because of this, the cryptanalysts would not have had the success that they did without the help of two things; German cryptographer’s mistakes in using the code and the espionage and tricks of the Allied forces.

A clue into the how the code was being run a certain day was often acquired from the mistakes of the Germans. For example, when German operators were picking keys they would often choose “three consecutive letters from the Enigma keyboard” or even use the same key as they had used previously (Singh, p.164). These mistakes, known as cillies, became vital to Bletchley Park’s decoding of the Enigma machine. Because they knew that some keys were more likely to show up than others, they could try their hunches first and would save valuable time if they were proven correct. Basically, the Enigma machine was still doing its job; it’s just that the operators proved to be too predictable. In addition, the Germans took efforts to make the Enigma machine more secure that often backfired and lessened the impregnability of the cipher. For instance, they decided that a scrambler couldn’t stay in the same position for two days in a row (Singh, p.164). This may seem to make it more random, but it actually excluded many of the possible scrambler arrangements that British cryptanalysts had to weed through.

When all else failed, however, and German mistakes and bright Bletchley park minds didn’t produce a crib, espionage and trickery became key. When they couldn’t find a crib, it seemed, British cryptographers would create one. By manufacturing situations where the German U-Boats would have to send messages with a specific location in the cipher, the British cryptanalysts could gain insight into the way the cipher was working. Because they knew the location of whatever the U-Boats had sighted (be it a convoy or a mine), the British had a bit of plaintext to work with. With this plaintext, they could employ Turing’s loop method and decrypt the scrambler and plug board settings of the day. All in all, using the openings found in the Germans operational mistakes and those created by Allied operations, the cryptanalysts at Bletchley Park could decrypt the Enigma, collecting valuable information that would help them win the war.

Espionage is the Key


Photo Credit: Tim Gage via flickr

One of the main reasons the Allied code breakers were able to crack the German Enigma cipher was espionage. Both stealing code books and obtaining documents from Schmidt gave the Allies the edge they needed to crack the Enigma machine several times. The Allies would be very far set back if they did not have access to the Enigma machine. Rejewski would never have made such quick progress on the Enigma machine if he did not have access to the documents explaining how the key was enciphered and a model Enigma machine. If Rejewski had not made such quick progress, the Allies would probably never had the break through that he achieved because Germany would have invaded Poland before the Polish could give the notes to the Allied nations. Espionage was also helpful for the guys in Bletchley Park. Stealing code books from German U boats was critical in deciphering the Enigma later on by using cribs that are established through the location of the U boats.

What is also important to note is that the Germans made the Enigma machine more complicated throughout the war without knowledge of the fact that the Allies had cracked it. This means that saying the Allies would have eventually cracked the code is not entirely accurate. Speed was actually pretty critical in attempting to crack the Enigma. Every time the Allies cracked a form of the Enigma, the Germans would make it more complicated later, so the Allies would have to reevaluate their attempts and use a slightly different method. What is important to note is that the Allies did not necessarily have to start completely over; they could just reevaluate and use their old notes since they had already cracked one form of the Enigma before. Without the espionage involved in stealing important documents and books, who knows if the Enigma would even have been cracked before World War II ended?

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