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I present to you the German Enigma machine. The Enigma machine was used to encode messages during World War Two. And it was a really interesting piece of equipment. It used several different rotors that were rotated to create a key for the encryption, and used a plug board and a keyboard for inputs. And so as we saw in the video with the Enigma machine, you would set the rotors to a particular key. And then when you press the key on the keyboard, and electrical current would go from that key, through the plug board, through the rotors, back out through the rotors, and then light up a lamp above. And so by pressing that key and holding it down, it would show you the letter that that letter should be encrypted to. Then, you would press the next key, another letter would light up, you press another key, another letter would light up. And each time you press a key, the rotors would advance one click changing the way that things were encrypted. And so of course, if you sat there and kept pressing the same key on the keyboard, you would notice that every single time you did that the letters that it would light up would be different every single time making you think that this is a very, very hard to break cipher. And indeed it was.
So as we saw, the Enigma machine consists of several rotors. Each rotor has 26 letters engraved around the outside, and it has 26 pins, each pin representing the input for one letter. And so you’d have a pin on one side, a whole scramble of wires on the inside, and then on the outside, you would have another contact that would go out. And so each pin was paired to one contact, but they were shuffled around randomly, so you really didn’t know how it was set up. And so of course, with just three rotors in the Enigma machine, that means there are over 17,000 possible combinations of three character positions of the Enigma machine rotors. So here’s an exploded view of showing the between the rotors where you have the pins on one side, making contact with the contacts on the other side. And so by sending an electrical current through one of the rotors, it would eventually go through the pins and contacts through each rotor until it would come back out the other side. And then of course, like we talked about, the Enigma machine uses a ratcheting system, very similar to an old analog odometer in an old car. Every single time you press a key, the ratcheting system would advance the outermost rotor, one click. And then of course, once that rotor has made a full cycle, it would advance the second rotor, one click, and then once that outside rotor has made 26 cycles, and the inner rotor has made 26 cycles as well, then the first rotor will be incremented one click. And so like it works just like an odometer, it’s very, very interesting the way they set this up.
But probably the most interesting fact is the way that the reflector works. So for example, let’s say you press the letter A on your keyboard. Then, it would go through the right rotor, the middle rotor the left rotor, and it would hit this special plate on the other end called a reflector, which would take that input on one pin and it would output it on another pin. Then it would go back through the rotors using a different path, and then it would hit the letter G and light up that light. But this right most rotor would then advance one position. So the next time you press the letter A, you would get an entirely different combination. You would have A which would go through this path, hit the reflector, come out this path, and then it would light up the letter C. So this makes decrypting messages really, really impossible. You never know what letter you’re going to get out based on the inputs unless you really know everything about how the position is set up. Finally, on the front of the Enigma machine, they included what’s called a plug board. And so what the plug board could do is you could swap the positions of two letters using these little wires. So for example, this system is set up to swap the letter S with the letter O and the letter J with the letter A. And so with this plug board, you can have up to 13 swaps, which gives you 10 million different combinations of keys that you might have to worry about. Of course, it’s interesting to note that the swaps are reflexive, so if J gets swapped with A, then A also gets swapped with J, so the same happens for both letters.
So all told, you have all sorts of different ways to set the key for the Enigma machine. You have the choice of the rotors and the ordering of the rotors. We saw three rotors, but toward the end of the war, there might have been as many as eight different rotors available that they could use. Then you have the initial position of the rotors. So the initial three letter key that the rotors were set to. You have the ring setting on the rotors, which shows where the rings go on the rotors, that way, it kind of changes the position a little bit more. And then you’d have the plugboard connections on the front, which are swapping different letters around. And so in theory, to understand how an Enigma machine is encrypting data, you would need to know all four of these things for each Enigma machine that you want to try and decrypt. And that’s a lot of information to keep in mind. Now of course, the other thing that they did is they had a specific operational pattern that they use when they were encrypting data using an Enigma machine. So the first thing they would do is they would set the wheels on the Enigma machine to the key from today’s codebook. The Germans carried around these code books that gave the keys for each day. And unfortunately, throughout the entire war, to my knowledge, not a single codebook was lost. In addition to the key settings, there was a particular way that the Enigma machines were operated. To operate an Enigma machine. First, they would set the wheels to the key from today’s codebook, the Germans used a paper codebook that gave different keys for each day of the year. And to my knowledge, those code books were not ever compromised during the war, they would always be burned or destroyed before any German camps were taken over. Secondly, the operator of the Enigma machine would then choose a unique key for the message. So they would choose a different key consisting of three characters for that message. So then they would use the daily key to encode the message key twice to avoid errors. So the first six characters of the message would be the message key encoded twice, then you would set the wheels to the message key, and start en crypting and sending the message. So not only did each day have a different daily key, but then each individual message used its own message key to send the data, so everything was really scrambled.
So if we look at this process, how do you think you’d go about cracking an Enigma machine? Take a minute to think about that. So obviously, the Enigma machine had many strengths. There were many different factors to the encryption, as we saw earlier. There were eight different wheels to choose from by the end of the war. And so depending on how you calculate it, there could be as many as 150 trillion different setups just from the plugboard itself. So altogether, it’s estimated there were 158 quintillion possible keys that you could use to decode an Enigma machine.
However, the Enigma machine came with very, very important weaknesses. The first and most important weakness was a letter would never encrypt to itself, because of the way the reflector worked on the plug boards and on the wheels. If you press the key A, you could press that key 26 times, and never once would the light for a light up because they were on the same circuit. And so with the reflector through the wheels, there was no way the current could come back through the circuit that it was sent out, which means that A would never light up for itself. Secondly, of course, the plug boards were reciprocal. And so by swapping two letters, you’re really just adding a substitution cipher on top of a really complex polyalphabetic cipher so the plug boards really didn’t do a whole lot in terms of making the combinations more complex, it just scrambled the letters a little bit. Another big problem they had was the wheels themselves were not similar enough, the wheels were so different, in fact that using some advanced mathematics, you could determine roughly which wheels were being used, just by the way the letters were distributed in the message that you received. And then of course, there were some poor policies and procedures around the Enigma machine. And one of the worst parts was the fact that they allowed message operators to choose the key. If your message operator in a foxhole during a war, and you’re asked to come up with three random letters all the time, every time you want to send a message, are those letters going to be truly random? Or are you more likely to pick some letters that have specific meaning to you like the initials of your loved one back home or your hometown, and they actually found out that that was a problem. A lot of German message operators were not picking truly random letters for the message keys. And then of course, they were encoding those same letters twice at the beginning of the message. So if you could decrypt the first three letters of the message, you had the message key that you could then use to decrypt the rest of the code. So that was not really that useful. So now let’s take a look at a second part of this video about how to decrypt a message that’s encoded with Enigma machine.