To appreciate the genius of the way in which the codes were cracked, it is first necessary to understand the workings of the Enigma machine, as well as the 'rotor'. The body of a rotor is about the size of a small ice-hockey puck. It is a disc, measuring about 8 cm in diameter, and is made of an insulating material like Bakelite. The rotor has a hole through the middle, so that it can be rotated on an axle, and there is a ring of 26 electrical contacts on the edges of both flat, circular faces of the disc. These brass contacts are like small buttons and, by looking directly at the rotor edge, it can be seen that each contact on the one face of the disc is connected by a wire to a contact on the opposite face. In addition to the rings of contacts, there is a knurled wheel and a loose ring. When the rotor is mounted on its spindle, the knurled wheel allows the operator to turn the rotor. The 26 letters of the alphabet are engraved on the loose ring, which can be turned and set on the rotor disk in such a way that any given letter lies over a particular contact. Thus, if the selected letter on the ring is 'A', then the contact over which it is set serves as the position for 'A' for that setting. The purpose of the rotor is to shuffle the electrical contacts, so that when a letter, such as 'A', is pressed on the keyboard, the rotor scrambles the connection and causes a light to glow under another letter, such as 'F'. The two rings of contacts are connected in a random manner so that the rotor is able to perform an 'alphabet substitution'.
The Bombe was used with success from the summer of 1940 onwards, to break messages enciphered on the simpler Enigma system used by the German Air Force. But the most important messages were those to and from the U-boat fleet, and these were enciphered on a much more secure Enigma system.
Alan Turing took on this problem, going against the prevailing view that it would prove unbreakable. Although he had crucial new ideas at the end of 1939, not much practical progress could be made. In 1940 they were desperate.
Fortunately, the military mind works in favour of the cryptanalyst, as the formats and protocols of military messages are rigid and stylized, quite unlike civilian language. This means that, by identifying the format of the message, it would be possible to work out what Bletchley referred to as the 'probable' words and phrases. For example, station identification codes informed the receiver of the message (or, in the case of Bletchley, the interceptor) of the identity of the sender and even what kind of message it was. Identification codes were capturable and, when linked to direction finding equipment, could he very informative, providing the cryptanalyst with a good guide as to the rotor settings, etc. Weather reports were short, to the point and coded before they were enciphered; again providing good grist for the mill of the cryptanalyst.
British Intelligence Service, sometime in 1938, contacted a Polish worker who was employed in a German factory making Enigma- machines, and persuaded him to build a big wooden model of the machine. They gave the Poles the necessary money, and the Polish Intelligence "acquired" the machine, by means not specified. Then, in the utmost secrecy, "the complete, new, electrically operated Enigma" was brought back to London. The British set to work, invented a device called the "Bronze Goddes", and were able to read German Enigma ciphers.
The emergence of the Enigma machine had marked the start of the electromechanical era in encrypting communications. Previously manual ciphers could be cracked by pen and paper but with Enigma the first computers were required.
That situation, Lobban argues, is analogous to the modern era with the advent of the internet and digital technology which is, as with the 1930s and 1940s, requiring a combination of partnerships, cutting-edge technology and human skills of the type Dilly Knox embodied.
"The computer and the internet have combined to produce new challenges in intelligence and security which require transformational changes in our organisations if we are to continue to be as successful in the 21st Century as we were in the 20th. We must become deeply technological organisations,"
The inter-allied intelligence operation Enigma - wrote a prominent American historian of cryptography - was "the greatest secret of World War II after the atom bomb" (1). The breaking of the sophisticated German machine cipher was the most spectacular event, in terms of difficulty and far-reaching consequences, in the entire history of secret writing. Operation Enigma was one of powerful weapons of the anti-Nazi war coalition but in contrast of to the atomic energy, which itself had come to light in the terrific holocaust of Hiroshima and Nagasaki in August, 1945, the secrets of the Enigma remained hidden and unknown to the public for the next almost three decades. Its details has been emerging only fragment by fragment from the darkness in which the governments concerned have felt it better to keep them.
Polish Intelligence were initially unable to break the German Enigma traffic, however driven by the imperative of finding what the Germans were up to, they, uniquely among other nations at that time, decided to try a mathematical approach. In 1932 a team of young mathematicians was set up. It included Jerzy Rozycki, Henryk Zygalski and Marian Rejewski (all of whom were products of the notable flowering of Polish mathematics in the 1920s and 1930s).
Rejewski quickly showed that mathematical techniques could be used to attack the problem of finding the message key by exploiting the German's cryptographic error in repeating the message key at the start of a transmission.
The problem that still had to solved was the internal wiring connections in each wheel. In this Polish Intelligence were helped by the French. The French were very interested in assisting Poland because they also were disturbed by the rise in German militancy and wanted an ally on Germans Eastern flank.
In 1939-40 Alan Turing and another Cambridge mathematician, Gordon Welchman, designed a new machine, the British Bombe. The basic property of the Bombe was that it could break any Enigma-enciphered message, provided that the hardware of the Enigma was known and that a plain-text 'crib' of about 20 letters could be guessed accurately.
Using these techniques the Polish cryptographers were, by 1938, reading some 75% of intercepted German Radio transmissions enciphered using the Enigma machine. They kept this a very closely guarded secret, telling no one of their successes.
Then in 1938 the Germans brought another two wheels into service so that the German operator now had to chose three out of five to put into the Enigma machine. This raised the amount of effort required to find keys way beyond what Polish Intelligence could provide.
In July 1939 with the invasion of Poland imminent, the Polish cryptographers decided to share their Enigma results with the French and British code breakers. At a meeting in the Kabackie Woods near Pyry just outside Warsaw all was revealed to the utter astonishment of the French and British. The Polish team gave them copies of the German Enigma machine and revealed the details of the Cyclometers, Bombas and Zygalski sheets.
About 1918, Albert Scherbius took his idea of the "rotating rotors" in a cipher machine to the German military. They weren't interested in his ideas at that point in time and so Scherbius took his idea to a German company called Gewerkschaft Securitas. That company bought his patents. The first Enigma machine was produced in the early 1920's. It was an electrical enciphering machine which provided "better" encryptions of messages than other machines at the time because of the rotating rotors.
The German Navy started buying Enigma machines in 1925 and they started to modify it. The German Army soon followed suit and they also modified the machine. Some of the modifications included adding or deleting some keys, the addition of the plug board and using more than three rotors.
The Germans placed a lot of confidence in the security of the Enigma machine because they thought that the probability of breaking a message would be too great for their enemies. They did have certain procedures on the operation of the machine. The Germans had manuals that the operator used to set the parameters of the machine for each day.