Type the next 3 (or 4) letters from the message to get the message key. Turn the rotors to the first 3 (or 4) letters of the message.Add the start position you noted down in step 2, and the encrypted message key you noted down in step 3, at the start of the message.Choose which messaging app you want to use and enter the address of the recipient.When you have completed the message, click the tape and select Send.Click the tape and Clear it, turn the rotors to the message key you chose in step 3, and then type your message.Remember these letters! Note down what letters are printed on the tape. Type 3 (or 4 as appropriate) new letters for the message key.Choose 3 (or 4 depending on how many rotors your machine model has) letters as your random start position and turn the rotors to these letters.Load the file with your agreed settings into the simulator. To send an actual message, follow these steps: First agree which machine model and settings you are going to use the simplest option would be to use the settings from one of the save files pre-installed in the simulator, but sender and receiver can make up their own settings together and each save them on their own device, or share a key phrase password and use it with the settings generator pages linked to above. To send and receive encrypted messages with the simulator, you need to do essentially the same things the real Enigma operators did. This had two security problems that were subsequently corrected: from September 1938 they switched to the operator choosing a different starting position for each message (in effect, an initialisation vector) and transmitting it before the encrypted message key from May 1940 the operator encrypted the message key once only.Īfter encrypting the message key, the operator turned the rotors to show the letters of the message key before encrypting the message body. Up to 1938, the German army procedure was to set a fixed starting position for the rotors (part of the day's settings) and to use that to encrypt the message key twice (to detect keying or transmission errors) at the start of the message. In the case of the Enigma, however, the message key was regarded as part of the secret shared between sender and receiver, therefore it was encrypted before sending.Įncrypting the message key doesn't add a lot of security ( mathematically it contributes less than 10 bits to the effective key length) and, given the security problems flawed indicator procedures caused in practice, the Germans may have been better off not doing it! Such a plain text transmission would be called an initialisation vector in modern encryption algorithms and is accepted security practice. The simplest thing to do would be to transmit the message key (the letters showing in the rotor windows) in plain text at the start of each message. There is a special page on this wiki which you can use to generate tables of random machine settings:Ī wireless station could have been part of more than one network, so the first part of the message (along with the date) would typically include a code (the discriminant) indicating which network, and hence which machine settings, it was intended for. Different tables were used for different "networks", representing different branches of the armed forces. Tables of machine settings for each day of a month were created and physically distributed in printed form. Security weaknesses in these indicator procedures were one of the main ways in which the Polish and British codebreakers were able to decrypt intercepted messages. The method of communicating the settings and message key is called the indicator procedure and the Germans used several different methods before and during World War II. 3 Sending and Receiving with the Simulator.
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