Wolfpack – The Enigma Machine

The Enigma machine is a device used to encrypt and decrypt radio messages. The Enigma uses a system of mechanical switches connected to rotating code wheels. The signal is then passed through a switchboard, before being passed to the top of the machine. The encryption key can be set by rotating the wheels located on the top of the device. The correct switchboard combination is already set when the game is started.

When a key is pressed, the corresponding cypher letter is lit on the top of the machine, and the encryption wheels rotate. This means that typing the same letter many times in a row will result in a seemingly random output pattern. This is what gives the Enigma its strength as an encryption device. The cipher is symmetrical, meaning that if a particular encryption key results in K being translated to F, then the same setting will translate F to K. To decrypt a message, the receiver simply needs to type in the ciphertext, and the output should be the plain text that the sender encoded, provided that both the sending and receiving machines use the same key settings.

Since the receiver must know what encryption key was used to send it, and the key changes as the message is typed, the message must always be preceded by the start encryption settings in plain text, followed by the encrypted message. This, however, presents a problem, as if the enemy has captured a machine, and has made the correct switchboard adjustments to it, they can decrypt the message. To avoid this, two encryption keys must be chosen: One public key, and one secret key. The public key is sent in plain text, and is used to encrypt the secret key. The secret key is then used to encrypt the rest of the message.

For example:

I want to send the encrypted message “HELLO THERE”. I choose a random public key: “PKJ”, and a random secret key: “GWP”. I first write down the public key in plain text: PKJ, then I set the encryption wheels to PKJ and type my secret key GWP on the keyboard. This gives me the output UFI. I write that down. I then set the encryption wheels to GWP, and type HELLO THERE, writing down the output. I can now send the message, which should look like this:

PKJ UFI FIKDX QBLQB.

When the receiving u-boat picks up the message, the radio operator sets their encryption wheels to PKJ, and then type in UFI, which gives them the secret key GWP. They then use that key to decrypt the rest of the message. Remember to never use a public key that can be used to guess the secret key, for example, public: BER and secret: LIN.

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