Gretag, Dr. Edgar Gretener AG, Zürich
überarbeitet am 28.2.2013
Gilbert Vernam, an engineer of the American AT&T, developed the idea to encrypt
a teletype punched paper tape using a second "key tape". Both punched tapes were combined
together adding the elements "hole" and "no hole" corresponding to "1" and "0",
the sum is used as the product of the encryption. When the punched tape generated at
the receiving site is combined with the "key tape", a tape with the original code can be generated.
This can be fed to a teletype printer and the original message can be read in plain text.
The Telecrypto 53 set is inserted between a transmitting ETK set and a telephone landline; at the receiving site, the pulses coming from the receiver are fed to the ciphering machine which will generate the signal to drive the ETK printer. This arrangement can be used for real time encryption.
The key consists of 12 characters and a number code with four out of eight numbers. The four permutation wheels at the left side and the advancement wheels at the right side of the key display window are moved electrically to set the key to start decryption. According to the number key, the switches 1 - 8 are set to the correct position.
The SPG (Schlüsselproduktionsgerät) is nothing else then a mechanical password generator. It is used to generate a true random message key, so that the operators did not use SUN, RAIN or the name of the unit commander every day. Similar password generators are used in the computer era, as man - made passwords are usually easy to crack with a "dictionnary attack".
The Telecrypto 53 has been produced by Dr. E. Gretener AG located at Zurich.
The Telecrypto 53 together with the printer ETK-R 55 has been in use over landlines with the signal troops, it turned out to be quite unreliable for shortwave communications and has been replaced by the KFF 58 for this purpose. In 1983, the ciphering machines and teleprinters have been withdrawn from troop use and most of them have been destroyed as the had been classified as secret equipment.
© Martin Bösch 14.2.2013