![]() ![]() By turning the rotor while leaving the letters stationary, the connections between letters change. One way to easily implement that, and it’s the way it’s done in the Enigma, is to embed all that wiring in a wheel/rotor. And even better, if they change each time a letter is encoded. An improvement would be for all those pairings to change. The ability to change the mapping is important because once someone deduces that G is the substitution for A, they’ll know that’s true for every G in the ciphertext. Rotating substitution cipher Enigma rotor wiring But those lines can be wires, electrically connecting each pair, which opens up the possibility of easily changing how the substitution is mapped through to the ciphertext. We could redraw the cipher as two alphabets with letters in alphabetical order, and draw lines between the paired letters. Adding Rotors Simple substitution cipher with wires Let’s take this further like the Enigma machine does. To decrypt it we do the reverse, look for each letter in the bottom row and substitute with the corresponding letter in the top row, getting HACKADAY. ![]() Similarly, looking for the A in the top line, we see we should substitute it with a G. Using the above cipher we look in the top line for the H and we substitute the letter below it, a Z. Let’s say we want to encrypt the word Hackaday. Most have seen how to encrypt messages using a simple cipher like this. Most recently the story of how it was broken was the topic of the movie The Imitation Game. Possibly the greatest dedicated cipher machine in human history the Enigma machine is a typewriter-sized machine, with keyboard included, that the Germans used to encrypt and decrypt messages during World War II. It’s also one of the machines that the Polish Cipher Bureau and those at Britain’s Bletchley Park figured out how to decipher, or break. But it’s really quite simple. The following is a step-by-step explanation of how it works, from the basics to the full machine. “It might come in handy for a future space civilisation spread through the solar system,” says Makarov, given that transmissions will take longer to arrive in space.To many, the Enigma machine is an enigma. QKD uses quantum mechanics to create the key, requiring back-and-forth communication, but in quantum Enigma, the key is pre-arranged, so the only transmissions are the messages themselves. Vadim Makarov, who runs a quantum hacking lab at the University of Waterloo, Canada, says quantum Enigma is more difficult to implement than QKD but has other benefits. Lloyd is now trying to build the machine: it might even fit into a typewriter-like form, he says. The switch to quantum mechanics changes the equation: increasing information on the part of the codebreaker no longer leads to a significant reduction in the key strength – unless the information is the key itself. But instead of electricity and rotors that change the settings, the hypothetical machine uses photons, with the quantum ability to follow two paths at once. To devise a quantum enigma machine, Lloyd preserved the basic idea of two people with versions of the same machine and shared settings. In other words, they turned an increase in information about the message into a reduction in the key’s strength. Turing and his colleagues relied on external information, such as knowledge that a message was likely to be about the weather, to make educated guesses at its content, which often led them to the key. If you know the settings – Enigma operators had books specifying them – the encrypted words can be typed into another Enigma machine to reveal the message. ![]() The change isn’t random, but depends on the initial rotor settings, which work as the key. Crucially, with each new letter, the path changes, so if you type the same letter again it will be encrypted differently – avoiding the repeated letter patterns that codebreakers rely on. Wired rotors do the scrambling by guiding an electrical signal along a certain path. ![]()
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