M-325

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M-325 in the National Cryptologic Museum , Fort Meade , Maryland

The M-325 (or SIGFOY) was a rotor key machine developed by William F. Friedman in the USA in 1936 . Between 1944 and 1946, 1,100 of these machines were used by the US diplomatic service. In 1946, the use of the M-325 was discontinued because it could not meet the expectations placed on it in terms of operational safety and speed. A patent for the M-325, filed by Friedman on August 11, 1944, was granted on March 17, 1959 (US patent # 2,877,565).

functionality

The functionality of the M-325 was essentially identical to the Enigma . Like the Enigma, the M-325 had three rotors that moved further in the course of the encryption and decryption and one reversing cylinder that did not move any further . As with some commercial Enigma variants, the reverse roller could be manually set to one of 26 positions. In contrast to the Enigma I used by the German Wehrmacht , the M-325 shown on has no plug board. According to, there was also a version with a plug board.

The switching of the three rotors was controlled with the help of transfer notches. The rotors of the M-325 each had five notches (see), whereas the rotors of most Enigma models only had one or two notches. (The rollers of the Enigma-T, however, also had five notches.) The movement of the rotors of the M-325 was therefore much more irregular than that of the Enigma I, which made unauthorized decipherment much more difficult. The rotor box shown on has nine compartments, which suggests that in addition to the reversing roller, eight further rotors were available, from which three were selected to operate the machine. From it can also be concluded that the rotors of the M-325 could only be inserted into the machine in one orientation.

service

As with the Enigma, the encrypted or decrypted characters were output via a lamp field. Under the lamps labeled with the characters of the alphabet were buttons that had to be pressed when the respective character was to be encrypted or decrypted. After each character was encrypted or decrypted, the operator also had to press another button that triggered the rotors to advance.

literature

  • Cipher A. Deavours, Louis Kruh: Machine Cryptography and Modern Cryptanalysis. Artech House Publishers, Dedham MA 1985, ISBN 0-89006-161-0 ( The Artech House Telecom Library ).
  • Cipher A. Deavours, Louis Kruh: The Typex Cryptograph. In: Cryptologia. 7, 2, 1983, ISSN  0161-1194 , pp. 145-166.
  • Louis Kruh: Converter M-325 (T). In: Cryptologia. 1, 1977, pp. 143-149.

Individual evidence

  1. ↑ Friedman M-325 - information and photographs.
  2. ↑ Cipher A. Deavours, Louis Kruh: Machine Cryptography and Cryptanalysis Modern , Artech House Publishers, 1985, ISBN 0-89006-161-0 , page 16
  3. ↑ Kruh, Louis and Deavours, CA (1983) 'THE TYPEX CRYPTOGRAPH', Cryptologia, 7: 2, 145-166 p. 154
  4. ^ A b Operating and Keying Instructions for Converter M-325 (T) Headquarters ( Memento of October 16, 2006 in the Internet Archive ), Army Security Agency, July 1948, scanned and transcribed by Bob Lord.

Web links