In the early 1930s, the Germans distributed a secret monthly list of all the daily machine settings. The Germans knew that it would be foolish to encrypt the day's traffic using the same key, so each message had its own "message key". This message key was the sender-chosen initial rotor positions (e.g., YEK). The message key had to be conveyed to the recipient operator, so the Germans decided to encrypt it using the day's pre-specified daily ground setting ("Grundstellung"). The recipient would use the daily machine settings for all messages. He would set the Enigma's initial rotor position to the ground setting and decrypt the message key. The recipient would then set the initial rotor position to the message key and decrypt the body of the message.