The image on the right shows a typical Cipher Machine D, consisting of
a bottom section with the actual cipher machine, a
double tape reader 77f
in the middle, and a control unit at the top.
The rearmost tape reader is for the (random) key tape, whilst the one at
the front is for the clear text tape or the cipher text tape, depending
on the mode.
The machine is intended for offline use and can be used
stand-alone (i.e. connected to a 5-level tape puncher), as a transmitter
(i.e. connected directly to the line), or as part of a data-entry setup
(i.e. connected to a telex unit).
The device uses the so-called Vernam Cipher
in which each character of
the plain text tape is mixed with one character of the key tape,
by means of an XOR-operation. When the key tape contains true random data
and the machine is used properly, this cipher is truely unbreakable.
Cipher Machine D was introduced in 1957 and was produced until the mid
1960s, after which it was succeeded by the M-190.
According to date codes on the components, the device shown here was built
in or after 1965. It has French labels 1 and was used by the French Army or
the French Foreign Ministry, in combination with a T-37 or
The device is very similar to the
Philips Ecolex II,
which was built around the same Siemens T.send.77f
double tape reader.
Around 1965, Schlüsselgerät D was succeeded by the similar but
more advanced M-190 mixer.
The device was usually labelled in German, but the one shown here
was made especially for the French Government and, hence, is labelled
in French. As all labels are removable, Siemens could easily adapt
the device for any country or customer.
The diagram below shows a view of the left side of the machine.
The name tag Schlüsselgerät D is missing here and has probably
been removed. It is usually present to the right of the other two tags.
The leftmost plate is of the double tape reader
(T.send.77f), which is
used as the heart of the complete device. The actual mixer
(i.e. the XOR circuitry) is located in the bottom section.
At the bottom of the left side are the connections for the mains network
and a teletypewriter (telex). Also present at the left is a hinged door
behind which a large socket with a connector is located. Apart from the
power switches, all controls are located at the top section. The device
has two identical 5-level punched paper tape readers. The rearmost (i.e.
the one closest to the control panel) is for the key tape. The one at
the front is for the clear tape or the cipher tape.
The block diagram below shows how the device works. At the left are the
two tape readers, one for the plain (or cipher) text and one for the key
tape. The 5-bit outputs of the tape readers is fed to the inputs
of a so-called mixer that produces the 5-bit XOR (modulo-2) of the individual
bits of the inputs. The XOR circuits in the mixer are built with electric
relays. Note that the inputs of the mixer are wired via connector H,
which is available at the left side of the machine. A shorting plug must
be present in the socket for normal operation.
The pinout of the plug is given below.
From the mixer, the 5-bit parallel signal is fed into a serializer, which
converts the data into a serial asynchronous protocol, allowing it to be
sent over a standard telex line or via radio. The line interface converts
the serial data signal into a regular 40 mA current loop telex signal.
The complete setup was known as Schlüsselgerätesatz D (cipher kit D),
extended with the number of the teletypewriter with which it was issued.
As a general rule of thumb, black units were commonly configured for
45 or 50 baud operations, whilst beige units were generally used for
75 baud operation, although there are exceptions to this rule.
The following setups are known:
Schlüsselgerät D with Siemens T-37
or T-37i teletypewriter.
In this case, the cipher machine would be supplied in a black enclosure,
just like the one featured here.
Schlüsselgerät D with Siemens T-68 teletypewriter.
As the T-68 telex machine was supplied both in black and beige, it is
likely that the cipher machine was available in these colours as well.
Schlüsselgerät D with Siemens T-100 teletypewriter.
In this case the cipher machine was most likely supplied in a beige enclosure,
in order to match the colour of the T-100.
Double tape reader
Cipher Machine D is built around a very popular double tape reader, known as
the Siemens & Halske T send 77f. Although initially intended for retransmission
equipment, it became a very popular component of some
One-Time Tape (OTT) cipher machines
in the early 1960s. The two tape readers are fully independent and are
not driven by a common axle. Instead, stepping is controlled by a solenoid.
Each tape reader delivers its 5-bit parallel output onto a connector at
the rear. The actual mixing and conversion into a serial signal is done
outside this unit.
- NSN 5815-25-105-4214
- Chiffrier-Zusatzgerät (Lochstreifenleser) 
Siemens & Halske T send 77 f
(als Zusatz zum Fernschreiber T 100 oder T-37 i)
Siemens & Halske, Wernerwerk München, 1964.
The interior of the rather heavy Cipher Machine D is easily accessible.
The bottom case shell
can be removed after losening just 3 bolts: one at the
left and two and the right side of the case. The die-cast
aluminium top cover
can be taken away after removing a large bolt at the top centre.
The image on the right presents a right-angle view of the machine, after
the top and bottom case shells have been removed. The double tape reader
can easily be identified towards the front of the device and appears to be
in great shape.
Mounted towards the rear is a control panel
with 4 push-buttons and a
set of 10 electric relays. It is mounted in such a way that the buttons
are reachable when the aluminium cover is fitted.
The control panel is connected directly to the bottom section by
means of a 14-pin connector mounted behind the double tape reader.
The actual mixer, i.e. the XOR circuitry, is mounted in the bottom section
that can be separated from the main unit. It is held in place by four
recessed screws. The bottom unit consists of the Power Supply
Unit (PSU), the line interface, 5 XOR relays, 1 large telex relay and
two small relays.
The image on the right gives a good view of the bottom section, which
is connected to the main unit via the two large black connectors at the top
right. The power supply and the line interface are at the left, with the
fixed rubber mains cable just visible at the top left of the image.
The relays, that are used at the heart of the XOR circuits are clearly
visible at the front right. They are used in combiation with a set of
rectifier bridges mounted behind them. They are just visible behind the
rightmost metal bracket. The large telex relay can be found at the far right.
At the left side of the device
is a hinged door behind which a sloped
marked H is mounted. All parallel data signals are available
on this connector, allowing it to be used 1 for testing, fault analysis
and external processing of the data.
A matching 30-pin shorting connector is fitted into the socket so that in
normal use, the 5-bit output of both tape readers is connected to the
two 5-bit inputs of the mixer.
Looking into the socket, the plug is wired as follows:
Once the two 5-bit data streams (text and key) are mixed, they are serialized,
so that the data can be sent through a regular telex line or via radio.
The serializer is mounted in the bottom section of the machine, inside a metal
enclosure, close to the actual line interface. The serial output is available
as a 50 baud 40 mA current-loop signal on the circular socket
at the left.
The shorting plug can also be used as a physical key for protection
of cipher security. When the operator has to leave his machine unattended
for a short period of time, he could remove the shorting plug from the
socket, so that the machine could not be used by others. This is why the
plug is easily accessible via the hinged door at the left of the machine.
MfS = Ministerium für Staatssicherheit, also known as Stasi.
The opressive security service of the former DDR (East-Germany).
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© Crypto Museum. Created: Monday 21 March 2016. Last changed: Monday, 13 January 2020 - 23:47 CET.