In my recent trip to the UK, I had a chance to go to Bletchley Park where they cracked the Enigma code used by the Germans in W.W.II. Bletchley Park itself was just saved from being bulldozed for a housing development. It looks like a dump, but it was a dump during W.W.II. There is one modest estate home but the rest of the buildings are mostly wooden shacks with pipes and wires running all over.
This is where the famed Alan Turing worked. The means of cracking the code were a machine called a Bombe (the Polish word for ice cream). The Bombe's were electro-mechanical machines that did an exhaustive search for the "key" used by the Enigma to encode messages. The key was a 3 letter code that was set into the 3 encoding wheels of the Enigma machine. Each wheel had 26 positions, one for each letter of the alphabet. The Bombe's were a Polish invention that the Polish government gave to the British before they were invaded. Hence the Polish name, Bombe.
The Enigma looked like a typewriter. When you push a key, it advances the first wheel one position and one of 26 lights is illuminated. The light indicates the encoded letter. The operator would press a key for each letter of the message to be encoded and write down the corresponding encoded letter. It was a manual process, the Enigma machine does not have a motor. The machines are not heavy, probably 10 LBS.
Pressing each letter advances the first wheel. When the first wheel advances one revolution it advances the second wheel one position. When the second wheel rotates once it advances the third wheel one position. It works exactly like a car odometer except that there are
26 positions on each wheel.
The wheels themselves have 26 contacts on each side. The wheels are stacked together in the machine so that all contacts from the 3 wheels touch. Thus, current flows through the three wheels. Inside each wheel there are 26 wires that connect the contacts on one side of the wheel to the contacts on the other side of the wheel. The pattern of the wire interconnects is different on each wheel. However, the pattern must be the same for all Enigma machines that can inter-communicate.
Bletchley Park had an actual Enigma bolted to a table that you could operate. I had a chance to try. It was a quite simple procedure. Dial in the key and then type in the message while writing down the encoded result.
The Bombe machines were all destroyed after the war along with the documentation. They are building a working replica. They got the drawings from the US government under the Freedom of Information Act!
The Bombe machine is quite simple. It is about 100 rotary switches that are all geared together driven by a 2 horsepower motor. Each switch has 26 contacts. The wiring to the switches is changed for each new code key search. There is a large jumper panel on the back where the connections are made. When the machine runs all switches rotate. When a circuit is made, meaning that the key is found, the machine stops. The key is then read out on 3 special dials.
At the peak, there were over 200 Bombe's running in the UK. Codes were cracked in about 1 hour. This is when the Germans were using 3 rotor Enigma machines. Then the Germans changed to 4 rotor Enigmas and the Bombe's were not fast enough. The German codes could no longer be cracked.
This led to the construction of the Colossus, the first electronic computer. The Colossus ran 5,000 times faster than all the Bombe machines. This allowed the German codes to be cracked again. Bletchley Park is also constructing a full working replica of the Colossus. That is about 1,500 tubes!
The Colossus had no memory. It did the same sort of exhaustive search as did the Bombe's, it was just much faster. The code to be searched was punched into paper tape and fed through a reader at 30 MPH. If they ran any faster the paper tape would overheat and catch on fire!
At Bletchley they had exhibits of the British coding machine. It operated on the same principle as the Enigma but had 5 wheels. It was much larger and motor driven. It also output the code as an electrical signal that could be sent over a phone line or over radio. It was about 2' by 2.5' by 2' high. It probably weighed 150 LBS. Not portable.
They explained how they broke the Japanese code. The Japanese had a problem with sending their language over a telegraph. There was no alphabet that could easily be encoded for telegraphy. Their solution was to translate all words used in military communication into 5 digit numbers. These numbers would be encrypted and sent. Once you understood the meaning of each 5 digit numbers, the code cracking process was no different than cracking the German code. Actually, even easier because you did not have to know a foreign language. To crack the German codes you needed to know German. To crack the Japanese codes you did not need to know Japanese!
Of passing interest, they had many of the props used to make the 2001 movie, Enigma. There is a 1/5 scale model of a German submarine. There is a full scale model of the conning tower and deck of a German sub. There are some Bombe props.
All in all, a great place to visit if you are interested in cryptography. For metalworking content, you can see the workable Bombe that they are constructing.
Pete.