Diving into the history of Cryptography III

So until now, we saw some of the really old ciphers. Now during the transition of 18th century to the 19th century, people wanted everything to be using machines and hence wanted their ciphers to be made mechanical. Hence they made a machine which will lead us to our 3rd type of cipher: Rotor machines.

3.) Rotor Machines

Here there’s this rotor mechanism where there is a rotor on the left side i.e. which is shown in the picture where that knob helps the disc in the middle to rotate and as we write in a typical typewriter, we can also write in this thing and for every letter we press on its keyboard, the disc rotates by one notch and hence the letter is changed to some other character. So here the central disc is working like a key. And for every letter pressed the key is activated and the original letter is assigned to some other letter. Here the disc rotates every time you press a letter. So basically it will either move up or move down by one notch and therefore it can be imagined as a two dimensional rendering discs.

So here when we press any letter more than once, there will be more than two variables assigned to it. Like if we press C three times then the output will be UJK and hence it will be quite a useful cipher method. But eventually it happened so that those cipher rotor machines were turned out to be very easy to decode by letter frequency method and by diagrams and trigrams it wasn’t that hard to predict the key and hence it was also declared to be easily breakable by cipher text only attack. As the time passed there came more and more complex rotor machines which used more than one rotors to encrypt the message. The most famous one amongst all was the ENIGMA Rotor machines. It used three or four or five rotor mechanisms and there were many versions of enigma machines. Very common of these machines used four rotors and also they moved at different paces. Plus you can get a key space of about 26⁴ different possibilities which is roughly around 2¹⁸ and that is already a very small key space. In fact today you can mount brute force on such a small key space and get the original plain text very, very quickly. You can even do it with your smart watch. And not to mention about some British cryptographers who mounted the cipher text only attack on these enigma machines back in the time of world war 2 which played a great role in understanding the strategy of the Germans.