Each day key settings for the Enigma cipher machine, essential for decrypting intercepted messages, had been distributed in printed booklets. These booklets specified the preliminary rotor configuration, ring settings, and plugboard connections for every day. A typical day’s entry may embody directions to pick rotors I, II, and III, set their rings to particular letters, and join specific letter pairs on the plugboard. Operators adopted these settings to encipher and decipher messages.
These settings represented the core of wartime cryptography. With out entry to those day by day keys, intercepting enemy communications was futile. Possession of the month-to-month publications afforded Allied codebreakers at Bletchley Park the power to decipher intercepted Axis messages, offering vital intelligence. This decryption effort performed a big function within the Allied struggle effort.