entering the scrambler at the G position, and if G was pressed the current would enter at A. The same connections applied for the current on the way out to the lamp panel. To decipher German military Enigma messages, the following information would need to be known. Logical structure of the machine (unchanging) The wiring between the keyboard (and lampboard) and the entry plate. The wiring of each rotor. The number and position(s) of turnover notches on the rings of the rotors. The wiring of the reflectors. Internal settings (usually changed less frequently than external settings) The selection of rotors in use and their ordering on the spindle (Walzenlage or "wheel order"). The positions of the alphabet ring in relation to the core of each rotor in use (Ringstellung or "ring settings"). External settings (usually changed more frequently than internal settings) The plugboard connections (Steckerverbindungen or "stecker values"). The rotor positions at the start of enciphering the text of the message. Discovering the logical structure of the machine may be called "breaking" it, a one-off process except when changes or additions were made to the machines. Finding the internal and external settings for one or more messages may be called "solving" – although breaking is often used for this process as well. Security properties The various Enigma models provided different levels of security. The presence of a plugboard (Steckerbrett) substantially increased the security of the encipherment. Each pair of letters that were connected together by a plugboard lead were referred to as stecker partners, and the letters that remained unconnected were said to be self-steckered. In general, the unsteckered Enigma was used for commercial and diplomatic traffic and could be broken relatively easily using hand methods, while attacking versions with a plugboard was much more difficult. The British read unsteckered Enigma messages sent during the Spanish Civil War, and also some Italian naval traffic enciphered early in World War II. The strength of the security of the ciphers that were produced by the Enigma machine was a product of the large numbers associated with the scrambling process. It produced a polyalphabetic substitution cipher with a period (16,900) that was many times the length of the longest message. The 3-rotor scrambler could be set in 26 × 26 × 26 = 17,576 ways, and the 4-rotor scrambler in 26 × 17,576 = 456,976 ways. With L leads on the plugboard, the