![]() ![]() It’s much easier to understand these operator failures-such as only slightly varying rotor settings between messages-when one is confronted with a physical version of an Enigma. But the code breaking also critically relied on instances of operator error to provide insight into the machine’s settings. (The plugboard added significantly to the cryptographic strength of Enigma machines, being, in effect, a user-programmable rotor.) Depending on the settings, the Mark 4 can act as either a four-rotor navy Enigma or a three-rotor army machine, and it can code and decode genuine wartime messages.Ĭracking the Enigma code required exploiting technical weaknesses of the rotor system, such as the fact that the reflector design means no letter can be encoded to itself. Operating the Mark 4 kit also requires you to decide how you are going to set up the plugboard, which lets you connect up to 10 letter pairs using patch cords. On the Mark 4, you enter the various settings using buttons above and below four 16-segment LED displays. The upshot is that every letter is encoded using a different combined substitution cipher, one that is not easily predictable without knowing the exact settings of the rotors.Ī War Machine: This Enigma can be identified as once belonging to the German navy, as it uses four encoding rotors-army Enigmas had only three. Every key press advances the first rotor one notch (so that now A becomes G, while B becomes H, for example), and after a certain number of steps, each wheel advances the next rotor along a notch. At the end of the series of rotors, a “reflector” passes the signal back through the rotors, where it then illuminates one of the letters on the Enigma’s display. When a key is pressed, a corresponding electrical signal is fed to the first rotor, whose output is used as the input for the next rotor. This acts as a basic substitution cipher, so that A becomes H, for instance. ![]() Each rotor hard-wires pairs of letters together in its own unique pattern. This made it impossible to fit the plugboard into place until I provided additional clearance by extending the front of the case with some spare beams of basswood.Īt the core of an original Enigma machine lies a set of three or four rotors. Unfortunately, when I tried to fit everything into the case, I discovered that the plugboard cable connector was pressing against the daughterboard that holds the Arduino Mega underneath the top panel. Initially-taking my lead from online pictures of some fully assembled kits-I built my case with the intent of mounting the plugboard immediately in front of the top plate. I built mine from basswood, making it a few centimeters taller than it needed to be so that I could have a space for storing unused plugboard cords underneath. The Mark 4 does not come with a case, so I had to make my own (although you can now buy hand-built cases from S&T Geotronics for an additional $350). ![]() Once the various mother- and daughterboards were populated and connected together, I downloaded the software from the Open Enigma website and installed it via a USB cable connected to the Arduino Mega. I found that prizing the contacts a little off the body of each LED made them much easier to solder to the right spot on the motherboard. These are small surface-mount LEDs and can easily slip out of place during assembly. The only truly fiddly part of this stage of construction was soldering the LED lights that form the Enigma machine’s alphabet display. I built a simple wooden case to house the circuitry (bottom). Spinning Electrons: The keyboard and displays of the Enigma are replaced by buttons and LEDs (top), while its mechanical rotors are simulated by an Arduino Mega (blue and white circuit board, middle). ![]()
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