OTT cipher machine (mixer)
- wanted item
The TT-360 was an off-line cipher machine for teleprinter networks (telex),
developed by Mils Elektronik in Mils (Austria),
probably in the 1970s.
The machine offers unbreakable encryption, by using the
Vernam principle to
mix the data from a clear-text tape with the random data from a
One-Time Tape (OTT).
It was probably the first mixing cipher machine (mixer) developed
The image on the right shows the only close-up picture of the TT-360
that we have available at the moment. The unit is 19" wide and has all
of its controls at the front panel. It consists of two products:
the 304 control unit and one or two 305 optical tape readers.
The unit shown on the right has two such 305 optical tape readers.
At the top are two paper tape readers:
one at the left rear, used for the clear-text, and one at the front centre,
used for the key tape which is fed from the tape reel at the right.
A version with just one paper tape reader was also available.
The single-reader version was used for online cipher systems and for
connection to an external tape reader. For transmission, the setup
was complemented by a 306 high-speed tape puncher, which is not shown
in the image above. The TT-360 was qualified for all types of transmission,
but was mainly used for Radio Teletype (RTTY) over short-wave radio links
(AM, FM and SSB).
The TT-360 was developed by Mils Elektronik
in the late 1960s or in the early 1970s,
and was one of their mainstream products for many years.
In 1975, it was demonstrated on the Mils Elektronik stand at the ITU
World Telecom Exhibition in Geneva, where the two devices were
The photograph below shows
two identical machines
The rightmost machine is connected to the high-speed 306 tape puncher.
The machine at the left is connected to a Siemens T-100 teleprinter.
Click here for the full image.
In 1979, it was still
shown on the Mils stand,
where the version with one tape reader was used in combination with a
Siemens T-1000 teleprinter. A double setup was used to demonstrate
The TT-360 was succeeded in the mid-1980s by the
ME-840 and eventually
by the ME-640.
Although the TT-360 was available from Mils for many years, it was by
no means the only mixer on the market.
Although it is difficult to establish
the first inventor of the mixer, it is assumed that the principle of using
the XOR operation (modulo-2 addition) for mixing clear-text and key,
was invented by Gilbert Vernam and that Joseph Mauborgne added the application
of truely random characters for the key. For this reason, a mixer is often
described as a Vernam Cipher.
The first practicle implementation of a mixer was probably the
that was developed in Germany during WWII.
As the machine was introduced relatively late
in the war, only a modest number of them were in operation when the war
ended. Some of them were confiscated by the Allies and send to the US.
The remaining units were destroyed.
Immediately after the war, the Norwegian manufactuer
the ETCRRM mixer.
It was later used on the
during the Cold War. The ETCRRM was a valve-based machine that was also
used by the Austrian Army and by NATO, until it was replaced by the Lorenz Mixer and the Siemens M-190.
In the late 1950s, the Dutch telecom operator PTT, developed the
their first valve-based mixer, soon followed by the fully transistorized
These machines were built by Philips Usfa in
Eindhoven (Netherlands), who later took over development from the PTT.
In 1963, Philips introduced the Ecolex IV
which would be their last mixer machine before they moved to
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