Telekrypto 53 , TC 53; made by Dr. Edgar Gretener AG, Zurich.
Gilbert Vernam, an engineer from AT&T, had the idea of encrypting a teleprinter paper tape with the help of a second tape, the key-tape. The character elements 1 and 0 resp. „Hole“ and „No hole“ are added together, the sum of the respective elements makes the cipher text. After the perforated key-tape is combined with the cipher text tape again, and and addition is done again, the plaintext is visible.
Together with cryptologists of the Federal military department, Dr. med. E. Gretener developed a cipher machine in which the Vernam method is used. In contrast to the original method with the use of a „key-tape“, the TC 53 uses a sequence of characters as the encryption key. So it is not necessary, to deliver a „key-tape to the receiver site, but with an identical starting position of the machine, the message can be deciphered, as long as the two machines work absolutely synchronously. However, if the key generator does „miss one step“, the machine at the receiver end must be advanced by the omitted steps wheels on both machines are back in the positions, then decryption can be continued.
The Telecrypto device is wired after the transmitting ETK teleprinter; on the receiver side, it converts the ciphered impulses into signals that are readable for the ETK teleprinter - real-time encryption is possible.
The key consists of a letter key of 12 letters and a number key of 4 out of 8 numbers. The four permutation wheels on the left side and the stepping wheels visible on the right side of the key window are electrically moved to their initial position with up/down switches; the numeric key indicates, which number levers 1-8 have to be set in the upper position.
Afters these preparation steps are done, the machine is ready to send resp. ready to receive. If the synchronization is out of sync, which occurs rarely on wired lines, but more often, if shortwave communication is used due to fading or interference, the machine with the missing steps has to be advanced one or more steps, until decryption can be continued - for this, the character counter is indispensable.
The situation was somewhat improved by the introduction of an advanced teleprinter ETK-R (radio), which had improved filtering and was less susceptible to interference.
The round SPG, key production device, is nothing more than a random letter generator, that generates a random message key which should be different from SUN, RAIN or the name of the company commander. Similar password generators are used again in the computer age, as electronically created passwords are more difficult to crack with a „dictionnary attack“.
The Telekryptogerät 53 was developed and produced by Dr. med. E. Gretener AG, Zurich.
The Telecrypto 53 together with the teleprinter ETK-R 55 were used by the signal troops for wired and wireless communication. In 1983, the material was withdrawn and most of it liquidated, which in this case will mean destroyed.