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← Gretag Bulk
Bulk encryption device
Gretacoder 603, or GC-603, was a
bulk encryption device developed
in the late-1970s by
Gretag in Regensdorf (Switzerland).
It was intended for the encryption of fast multiplexed telephone and data
channels at speeds between 32 kbits/s to 2 Mbits/s.
Data is exchanged in full-duplex (FD) time-division multiplex (TDM).
The device
is based on the nearly identical military GC-601.
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The device is housed in a heavy 4U 19" rackmount enclosure, with heavy grips at
either side. Power is connected to the socket at the right. All further
connections and some controls are at the left. At the center is an empty
space with two metal stubs for the separate key loading device.
The image on the right shows a typical GC-603, with the key entry
unit missing. A typical setup consisted of two such devices: one at
either side of a data link. Peripheral equipment should be connected
to the MUX socket on the front panel, which accepts bundled (multiplexed) data
traffic.
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A physical key is used to turn encryption on or off, using
the lock at the upper edge of the front panel.
It is likely that the GC-603 was suitable for exchanging (computer) data
and voice traffic (telephone) simultaneously.
The military origin of the machine
is clearly visible at the front panel, which is partly painted in
a military green colour and has four military sockets for the peripherals.
At present, not much is known about this device. According to the former
owner, it was used for communication via satellite between two bank sites:
one in Switzerland and one in the far-east. This is supported by the DYMO
labels that were present on the devices when we received them.
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For maximum security it is necessary to alter the cryptographic key(s)
at regular intervals. In a military environment, keys are generally
swapped at least every 24 hours. The Gretacoder 603 can hold several
keys, allowing a new key to be entered whilst the previous one is
still in use.
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Keys are entered into the GC-603 by means of a
proprietary key transfer device,
also known as a fill gun
or filler.
The image on the right shows the key transfer
device that was used with the Gretacoder 603. It can be attached to
the two metal stubs at the center of the front panel and should be
connected to the socket marked KEY.
Another proprietary unit that was supplied with each GC-603,
is a 3-position rotary switch, mounted on a military connector.
It should be connected to the CONTROL socket on the front panel
and is used to select the required MODE.
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The switch has three positions: OP, LP1 and LP2.
OP probably means: operate, whilst LP1 and LP2 are
probably used to select which KEY is being loaded with the key
entry device shown above.
The red button - marked E – can be used to erase the KEYs
in case of an emergency or compromise.
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© Crypto Museum. Created: Thursday 06 August 2009. Last changed: Monday, 01 April 2019 - 08:01 CET.
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