64 kb/s serial link encryptor
Gretacoder 524 was a link encryptor, developed by Gretag
in Regensdorf (Switzerland) in the early 1990s. It was intended for the
continuous encryption and decryption of serial (RS232) data at speeds up to
64 kb/s (synchronous). It was available with a variety of interface options.
All controls are at the front panel, together with two security modules (SM),
left and right, and a physical key.
The physical key locks the right SM and prevents the case from being opened.
The user interface consists of a series of buttons and an 2-row LCD display
at the top left.
The image on the right shows the front panel of a typical Gretacoder 524.
The case and the front panel layout is identical to that of the later
(and faster) Gretacoder 605. It is also identical to
the later X.25 variant, the Gretacoder 545 , although the case of the
latter was grey.
The Gretacoder 524 was part of a range of encryption devices that were
released over time, consisting of the 522, 524, 526 and 605 models,
that are more or less (backwards) compatible with each other, differing
only in speed and interface. To allow customization, the interface was
generally implemented as a separate daughter card, making the unit
suitable for wide range of applications and networks.
The device shown here supports the X.21 standard.
In 1991, Gretag was acquired by AT&T
(USA) and became known as
AT&T Gretag Data Systems AG, hence the reason for the
AT&T logo on the front panel.
AT&T also took care for the US sales of the Gretacoder range.
The 524 was succeeded by the improved and faster
Gretacoder 605 in the mid-1990s.
By that time the company was taken over by IRE and the AT&T logo
Please note that the Gretacoder 524 does not contain a physical MODEM.
It can only encrypt serial data in a variety of formats, but needs an
external modem in order to connect it to the outside world (e.g. via
telephone lines). Two separate proprietary connectors are available at the
back. The leftmost one connects to the device that needs to be protected
(plain text), whilst the rightmost one delivers the cipher text.
The Gretacoder supports two encryption standards: (1) Gretag's own
proprietary block cipher with a key length of 64 or 128 bits, or (2)
industry standard DES with a key length of 56 bits .
The latter was supplied for customers who wanted an industry standard,
despite the fact that by the early 1990s DES increasingly became
critisized as being unsafe.
The in-house developed 128 bit key block cipher provided much stronger
The Gretacoder 524 is built inside a rather neat cream metal case,
that measures only 22 x 7 x 36.5 cm. The case consists of two parts:
A metal frame holding the PCBs and the front panel, and a cream
outer shell. The latter is held in place by just two large bolt at the rear.
The outer shell can only be removed when the two bolts are taken out
(at the right of the front panel) is released.
The internal frame
holds the front panel and two PCBs:
the Main PCB at the bottom and a
smaller interface board at the top.
Depending on the customer's requirements, a different interface board
would be used. The interface connects to the main PCB by means of a
40-pin ribbon cable.
The interface shown here has two proprietary rectanglular connectors,
marked PLAIN and CIPHER.
At the heart of the main PCB is the M80C154 microcontroller, which is
compatible with the industry standard 8051. Several supporting chips
are present (e.g. RAM and serial interfaces) and the firmware is contained
in EEPROM. Encryption and decryption is implemented in
two custom chips on the main PCB.
At the rear, the main PCB has a female DE9 socket marked REMOTE CONTROL.
The purpose of this socket is currently unknown, but it seems to be a
standard asynchronous RS-232 port, probably used for a controlling terminal.
The PCB was designed to hold two DB25 connectors but these are unused in
this version of the 524 as the function is taken over by the interface board.
Apparently, the DB25 connectors were hardly used as they were omitted in
As Gretag is no longer in business, background information about the
company and its devices are very hard to find.
Unfortunately, we have no further information about this device at
present. If you have more, different or better information, please
contact us. Your help is appreciated.
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© Crypto Museum. Created: Sunday 26 May 2013. Last changed: Tuesday, 14 May 2019 - 09:44 CET.