Frode Weierud provides a summary of the T-43 device."The T-43 was used by the Germans on sensitive, high level communication links in the 1944-45 time period. It used one-time punched paper tape for encryption and decryption instead of mechanical cipher wheels as in the other T-series models. In practice, the key tape was generated by running a fifty-meter long loop of random tape over and over through a T-52d machine with the T-52d punching out the key tape as long as desired. The key tape was not random in a true sense, but it was unpredictable for all practical purposes and secure.
A serious electrical defect in the T-43 was discovered by radio engineers and corrected. This defect had actually rendered the T-43 insecure. Using an oscilloscope, it was observed that at the instant of encipherment, the keying character was electrically out of phase with the plain-text character by a small amount. As a result, minute inspection of the ciphered characters on the oscilloscope permitted the separation of the composite cipher characters into their plain-text and key-text elements resulting in a “solution” without having to go through cryptanalysis".
|T-43 in a wooden case.|
|T-43 in a metal case.|
|Both images in this table provided by Klaus Kopacz|
1) Klaus Kopacz
2) Frode Weierud <frode.weierud(at)gmail.com>