![]() ![]() Table 3: The effect of rotation on the character substitution map I've created an example of this in Table 3 below. When a rotor is rotated by one position, all of the characters in that rotor's character map are shifted by one position. This is where the rotating part enters the picture.Īs their name implies, one or more of the ENIGMA rotors rotate during the encryption process. However, assuming the substitutions remained the same for every character, even if a character went through ten thousand mappings, the end result would be a simple substitution cipher. With this arrangement of three rotors and a reflector, the input character would undergo seven remappings (three inbound, reflection, and then three outbound) before a lamp was illuminated. Of course, the story isn't over quite yet. That same setting of the rotors will take an encrypted message and output the original message. This means you need only one arrangement of the rotors, which becomes the key, to encrypt a message. Then, if you typed the letter F on the keyboard, it would illuminate the lamp under the letter D. Letter never encrypts to itself (allows known plaintext attack).The reflector is also significant because in one step it converts the set's substitution from an asymmetric mapping to a symmetric mapping! Thus, if you were to input the letter D by typing it on the keyboard of the machine with the rotors shown in Figure 1, the machine would output the letter F by illuminating the lamp under the letter F. Operators choose poor message keys (e.g., “BER”, “LIN”, “HIT”, “LER”, “JJJ”, “QWE”). Vulnerabilities Encryption of doubled indicators reveals information about rotor positions. When the center wheel arrow reaches the window, remember to move BOTH center and left wheels! īreaking Enigma Poles intercept commercial Enigma in the mail, 1928 Recruit math students at Poznan University, 1929 Poles (Rozycki, Zygalski, Rejewski) break the 3-rotor machine, 1932-1939 Overwhelmed by 2 new rotors in 1938 Poles hand over methods and machine copy to British and French in 1939 Government Code & Cipher “School” created at Bletchley Park, 1939 Rollover When the “notch” arrow reaches the window, move the wheel to it’s left up one row before encoding. Trace through each rotor, matching like letters. “Manual” Electricity Start at “E” on the right column. Initial Setting Rotors I, II, and III “ Window settings” of “M-C-K” Įncode a letter (First!) Advance the right-most rotor (III) by moving it up one row. Sample Encode Rotor order: I, II, III Rotor setting: M, C, K Encode the letter “E” Plugboard and rotor “ring settings” are not modeled. Reflecting rotor is replaced by a matching group of letters on the left. Keyboard and Lamps are replaced by a vertical list of letters on the right. ĭecoding: Message Set rotors to “M-C-K” (13-3-11) Type remainder of message: “ QMJIDO MZWZJFJR ” becomes “ ENIGMA REVEALED ”! Ī Paper Enigma Machine Each rotor is modeled as a strip of paper the electrical contacts are replaced by matching letters on left and right side of the strip. Confirm it decodes to “MCK MCK” (a valid message key). ĭecoding: Decode Indicator Type in message indicator: “NWDSHE”. Complete message is then: NWDSHE QMJIDO MZWZJFJR ĭecoding: Initial Setting Setup is the SAME for encoding and decoding. Type body of message: “ ENIGMA REVEALED ” encodes to “ QMJIDO MZWZJFJR ”. Įncoding: Reset Rotors Now set our rotors do our chosen message key “M-C-K” (13-3-11). Encoded with the daily setting, this becomes: “NWD SHE”. E.g., I would begin my message with “MCK MCK”. Įncoding: Transmit the Indicator Germans would transmit the indicator by encoding it using the initial (daily) rotor position…and they sent it TWICE to make sure it was received properly. Say, I choose “M-C-K” (or 13-3-11 if wheels are printed with numbers rather than letters). Įncoding: Pick a “Message Key” Select a 3-letter key (or indicator ) “at random” (left to the operator) for this message only. Setup: Initial Rotor Position We’ll use “M-I-T” (or 13-9-20). Setup: Plugboard Settings We won’t use any for our example (6 to 10 plugs were typical). Setup: Rotor Ring Settings We’ll use A-A-A (or 1-1-1). Setup: Select (3) Rotors We’ll use I-II-III How to Use an Enigma Daily Setup Secret settings distributed in code books. Scrambling Letters Each letter on the keyboard is connected to a lamp letter that depends on the wiring and position of the rotors in the machine. Invention of Enigma Invented by Arthur Scherbius, 1918 Adopted by German Navy, 1926 Modified military version, 1930 Two Additional rotors added, 1938 The Enigma Machine History of Computing DecemMike Koss
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