Lorenz SZ40
1940 · Lorenz Attachment · Work 462 of 1,871
A cipher attachment the size of a small filing cabinet, twelve thin flat wheels of differing diameters mounted side by side on one common shaft behind a hinged metal cover standing open, each wheel a smooth rimmed disc carrying a ring of tiny movable cam lugs around its edge, the lugs set some raised and some lowered, small numbers engraved beside the lugs, a teleprinter with a keyboard of round keys standing beside it and connected by a short cable, the attachment in a grey painted steel housing on a steel table, a single work lamp from above at an angle, the brass discs catching the light, the teleprinter room behind in darkness.
- What it was used for
- A cipher attachment between teleprinter and radio transmitter for the long-distance links of the German high command — traffic above the Enigma level; The National Museum of Computing speaks of the enciphered teleprinter communications of the German High Command. Tiltman lists twelve wheels with cycles prime to one another: 23, 26, 29, 31, 37, 41, 43, 47, 51, 53, 59 and 61. Five chi wheels step with every character, five psi wheels only when the two motor wheels release them; the arithmetic is modulo 2 in the five-unit teleprinter alphabet. Copeland counts twenty-six links known to the British at the time of the 1944 invasion. Tiltman names early transmissions between Vienna and Athens in the summer of 1941, often very long; he remembers one of about 16,000 characters.
- What was new
- The key tape of Vernam's principle was gone: a machine generated the stream itself, continuously, at teleprinter speed, in both directions — as the Siemens T52, built from 1932, already did. The 501 cams on the twelve wheels — the sum of the wheel lengths Tiltman gives — and the irregular psi movement made the traffic seem unbreakable. What opened the system was an operator. Tiltman describes two messages of 30 August 1941, one of 3,976 characters, the other about 500 characters longer, both carrying the same twelve-letter indicator HQIBPEXEZMUG. In about ten days he carried the recovery of the key through to the end of the shorter one. After that, he writes, no progress was made for about four months.