One-time Tape cipher machine (mixer)
The M-190 was a cipher machine
for teleprinter communication (telex),
built by Siemens in the early 1960s.
Its operation is based on the Vernam Cipher
and the machine therefore belongs to the so-called
or One-Time Tape
The M-190 can be seen as one of the successors to the wartime
that was built on the chassis of a T-37 teleprinter.
In the German Army the machine was also known as LOMI after its predecessor,
the Lorenz Mixer.
The principle of a mixer machine is that a plain-text character
from one paper tape is mixed with a random character from a key
tape, resulting in a cipher-text character.
As the mixing is done by means of an
exclusive-OR (XOR) operation
(also known as modulo-2 addition),
the same key tape character is mixed with the cipher-text
at the receiving end, in order to recover the plain-text.
The image on the right shows a typical Siemens M-190 cipher machine,
with both the clear-text tape and the key-tape loaded. An identical
key-tape has to be used at both ends of the link.
It is also important that the key-tape is at the same starting position
at the sending and receiving end. The M-190 can be used for both
offline and online operation. For offline use, the plain-text is
previously recorded onto a blank paper tape, using a standard teleprinter,
such as the Siemens T-100.
The tape is then played back, using the frontmost
paper tape reader (perforated tape).
When used online, the teleprinter is connected
directly to the M-190, and the frontmost paper tape reader left unused.
Instead, the key-tape is automatically advanced by one position,
each time the operator types a character on the keyboard.
Online use of cipher machines is often considered unsafe, as it may
reveal operator's characteristics, such as typing speed.
Furthermore, it is prone to mistakes as an operator may
accidently leave the machine in plaintext mode.
In order to avoid plaintext revealing mistakes, the M-190 has two
large coloured lamps at the front right of its control panel.
When the RED lamp is ON, the system is operated in plaintext mode.
Only when the GREEN lamp is ON, encryption is enabled and
transmission of text is safe.
Although the M-190 can be used with virtually any teleprinter
brand and model, it was commonly used in combination with
the equally coloured contemporary
Siemens T-100 teleprinter
The M-190 was used for many years by NATO and was compatible with
other NATO mixer machines,
such as the ETCRRM
and the Philips Ecolex IV.
It was also used for several years on the
from 1980 onwards, until it was superceeded by computers in 1988.
From the mid-1980s onwards, electro-mechanical mixer machines
like the M-190 were gradually replaced by fully electronic
teleprinters and eventually by computers. Although some teleprinter
links remained operational into the early 2000s, they have now
been phased out completely. Most machines have subsequently
been destroyed and are now highly wanted collectors items.
At the exhibition Secret Messages
held between October 2008 and February 2009
in Museum Jan Corver in the Netherlands, we had the unique opportunity
to connect two fully operational M-190 machines together in a small network.
The setup was used to demonstrate the practical use of
equipment to the audience.
The image on the right shows former intercept-operator Louis van Erck
(at the rear)
and Crypto Museum curator Marc Simons (at the front) each sitting behind
a Siemens T-100,
exchanging messages at typing speed using two M-190s.
For the demonstration, the two teleprinter systems were connected
together in a so-called current loop, using a line simulating device.
The two M-190 machines were loaded with identical key-tapes that had
been prepared prior to the event. Both machines were used in online
mode. Before starting, both key-tapes had
to be set to the same starting position. When typing text on one
machine, the same text would be printed at the other end. It was
also demonstrated what would happen if the key-tape on one machine
was shifted by just one position.
During the Cold War, the Americans and the Russians installed the
so-called Washington-Moscow Hotline
(sometimes referred to as the
Red Line), allowing direct communication between the two
parties in an attempt to avoid conflicts .
The Hotline was established in 1963 and initially consisted of two
pairs of data links,
using the ETCRRM one-time pad cipher machine,
built by the Norwegian company STK,
in combination with Siemens T-63 teleprinters with Cyrillic alphabet.
In 1980, the aging equipment was replaced by newer teletype units
and Siemens M-190 cipher machines. The image above shows the Hotline
terminal room in the NMCC at the Pentagon, with the M-190 clearly
visible in the foreground. The picture was taken on 27 August 1985,
shortly before the Hotline was superceeded by IBM computers
as shown in the image below .
The image above shows the other side of the Hotline terminal room
in the NMCC at the Pentagon on 14 November 1985 . Four IBM PCs are
visible in the background, complete with facsimile units (fax).
In the foreground, the Siemens M-190 is still visible. Although the
Hotline functionality was taken over by Fax, teleprinter lines
were used as backups until 1988 .
➤ More about the Hotline
Like most cipher machines of the mixer-class, the M-190 is not
(and never was) classified. It is the combination of the machine and
a NATO-issued cipher tape, that was classified as NATO SECRET.
Because of the fact that one-time pads (OTP)
were used with the M-190,
it is impossible to use the machine to break old intercepts, as all
original OTP-tapes were destroyed immediately after use.
Only a few M-190s have survived as most of them were destroyed
in the early 2000s.
- Data transfer rate: 45.45, 50 or 75 baud (368, 400 or 600 char/min)
- Line voltage: -120V
- Line current: 40mA
- Driving voltages: -24V and -120V
- Motor: 220V AC, 50-60Hz, 80W, asynchronous, 2500 RPM
- Dimensions: 27 x 33 x 61 cm
- Weight: 25kg
- Siemens & Halske AG, Mischgerät M-190, Beschreibung
Description (German). A22261-A190-A1-0-18. August 1962.
- Siemens & Halske AG, Mischgerät M-190, Betriebsanleitung
Operations and technical description (German). A22261-A190-A1-0-30. July 1965.
- Peter Koop, The Washington-Moscow Hot Line
Retrieved January 2013.
- AP, Photograph of Siemens M-190 and teletypes in the Hotline room
27 August 1985. Retrieved November 2012. Image kindly supplied by .
- Scott Davis, Images of Us-Soviet Hotline
© Time Inc. LIFE magazine, 14 November 1985, Arlington, VA, USA.
Retrieved January 2013.
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