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Crypto AG Voice CRYPTOVOX →
Wideband voice encryption unit · CRYPTOVOX
CVX-396 was a military-grade voice encryption device,
developed around 1976 by
Crypto AG (Hagelin)
in Zug (Switzerland). The device was intended for use
in combination with the PRC-77 radio,
but was also suitable for other
military radio sets
[1].
In the Swiss Army, a variant – known as
SVZ-B 1 – was used from 1983 to 2008, after which is was succeeded
by the SE-x35 [2].
It was supplied to the German Bundeswehr
as a rebadged product by Telemit
in München (Germany).
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The device is housed in a strong aluminium enclosure that measures
280 x 270 x 70 mm and weights less that 4 kg. Although initially
designed for
use in combination with the PRC-77 radio,
it is suitable
for any military VHF or UHF radio set that has a so-called X-MODE.
All controls and connections are at the front.
In most setups, a single cable between socket PL2 and the radio will
be sufficient, but if necessary, a handset can be connected directly
to the U-229 socket (U-183/U) at the top left. At the right are
a keypad and a display for entry of the key.
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Development of the CVX-396 dates back to 1975, as a prototype was shown
in 1976/1977 in a lecture by Crypto AG's chief developer
Oskar Stürzinger at
the ETH in Zürich [1]. The CVX-396 was based on the earlier development of the
CSE-280
(1971 - 1973) which was Crypto AG's first real voice encryption device.
It is entirely built with discrete logic components.
In 1983 a national (and arguably more secure)
variant — known as SVZ-B 1 — was introduced in the
Swiss Army [2].
The device was in production until 1990 and was used in several countries
until at least 2008.
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SVZ-B = Sprachverschlüsselungszusatz
Breitband (wideband speech encryption add-on) [2].
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All controls and connections of the CVX-396 are located at the
device's front panel, as shown in the diagram below. At the left are the
sockets for connection of the power, the radio set (PL2) and a
handset (AUDIO). At the centre is a 2-position switch that allows
selection between Plain (P) and Crypto (C).
On the SVZ-B, this switch
has 3 positions, allowing two different keys to be used.
At the right is a numeric keypad with a 6-digit red LED display,
that are used for entering the cryptographic key(s). This section
can be covered by a locked door, for improved crypto security.
Each key consists of 28 decimal digits that are entered as 7 groups 1
of 4 digits each.
To enter a key, press (✱). Next, enter the group number (1-7)
followed by four digits and a (✱). Repeat this process until all
groups have been entered. A key is now loaded and the device
is ready for use.
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In case of an emergency, the cryptographic key(s) can be purged by
pressing the (✱) and (0) buttons simultaneously. This process
is known as zeroizing. Unfortunately, this is only possible
when the door over the keypad is unlocked, which means that in normal
operation (i.e. with a locked door), the device can not be zeroized.
This might be considered a design flaw.
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On the SVZ-B, each key consists of 36 digits that are entered as
9 groups of 4 digits each. Furthermore, the SVZ-B allows two keys
to be stored.
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Within the Swiss Army, a variant of the CVX-396 was used from 1983
onwards. It was designated SVZ-B 1 and has improved security as each
key is 36 digits long, whereas the cryptographic keys of the regular
version (used for example in the German Bundeswehr) were only 28
digits long.
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In addition, the SVZ-B allows two cryptographic keys to be stored
simultaneously, whereas the CVX-396 can hold only one key. The image
on the right shows a typical Swiss Army setup with three SVZ-B units
at the top. The key-loading procedure is
printed inside the locked door.
Government procurement for the SVZ-B started as early as 1977.
The Swiss military were initially very impressed with the device's
weight and the
intelligibility of the speech, which were much better than that of
its competitors Siemens-Albis
and Gretag.
It clearly was the 'optimal solution'.
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But there were also doubts. The Swiss military cryptographers
who had evaluated the CVX-396, found its encryption algorithm —
which had been approved by CIA
and BND for export —
far too weak, and summoned experts from Crypto AG to Bern.
On 2 March 2020, three weeks after
the revelation of Operation RUBICON, 2
former Crypto AG employee Jürg
Spörndli revealed in an interview that the Swiss military allowed the
firm to submit a better proposal, which they did [4].
The improved algorithm was accepted and the Swiss military subsequently
ordered 6900 units.
In the interview, it was also revealed that the Swiss Army was well aware
of manipulation of the encryption algorithms by foreign intelligence
services. According to Spörndli, the Swiss federal cryptologist stated
'We know what you are doing, we know about the double game'.
It startled Spörndli, and made him think of the days in 1974, when the Yugoslav
Army had discovered a similar weakness in the
MCC-314 device.
At that event, they had supplied an improved algorithm.
➤ Operation RUBICON
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SVZ-B = Sprachverschlüsselungszusatz
Breitband (wideband speech encryption add-on) [2].
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Operation RUBICON
was a secret German/American operation, in which the German BND
and the American CIA had purchased the Swiss crypto manufacturer
Crypto AG in 1970, and used it to spy on other nations.
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The CVX-396 is known to have been used with the following radio sets:
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The AN/PRC-77 radio
was in fact a PRC-25
that had been given a solid state RF power amplifier, and
was modified for the connection of
digital voice encryption equipment,
by adding a so-called X-MODE to the circuitry.
When in X-Mode, the filters in the audio path of transmitter and receiver are
bypassed so that the full bandwidth of the set can be used.
➤ More about the PRC-77
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The CVX-396 is housed in a strong aluminium enclosure, similar in
design and width to the case of a
PRC-77 radio set. It consists of
a die-cast aluminium front panel with a single case shell behind it.
The case shell is held in place by for hex bolts that are located
behind the two grips.
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After loosening these bolts, the case shell can be
separated from the front panel.
This reveals the interior,
which consists of a black plastic frame with 8 PCBs that are slotted
into a backplane that is mounted to the rear of the front panel.
An additional PCB is fitted inside the front panel.
The image on the right shows the interior as
seen from the rear.
Note that there is no microcontroller and, hence, no firmware that
controls the device. Instead, encryption and decryption is entirely
done by means of shift registers, built from discrete logic components.
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Most PCBs are EUROCARD size (16 x 10 cm) and are slotted into
the packplane by means of a 2-row DIN connector. The only exception is
the internal power supply unit (PSU)
which is connected to the backplane
by means of the DE9 connector. Note that the
second board on the left
holds the backup batteries
that retain the key(s) in the internal registers.
Also note that the two boards at the top right
are sandwiched.
At the lower left is an empty slot for expansion.
As we don't have access to the original circuit diagrams, we are showing
the PCB numbers in the images below.
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Power 10 — 30V DC Consumption < 1.2W Keys 1 Key length 28 decimal digits ( ~ 67 bits)
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Power 10 — 30V DC Consumption < 1.2W Keys 2 Key length 36 decimal digits ( ~ 100 bits)
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At the top left of the front panel is a
standard (US/NATO) 5-pin U-229 socket
(U-183/U)
for connection of a handset. The pinout of this socket
is given below, when looking into the socket.
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- Ground
- Speaker
- PTT
- Microphone
- not connected
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As preset, the pinout of this connector is unknown.
If you can provide this information, please contact us.
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Socket PL2 is used for connection to the radio set. It carries the audio
input and output lines, as well as the power lines.
As preset, the pinout of this connector is unknown.
If you can provide this information, please contact us.
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At present, no further information about the CVX-396 and the SVZ-B is
available to us. We are currently looking for operating instructions, technical
documentation and information about the pinout of the connectors at the front.
We would also like to know where and how the CVX-396 was used.
If you have any additional information, please contact us.
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Retrieved from HAMFU History, December 2018.
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Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Friday 21 December 2018. Last changed: Monday, 02 March 2020 - 11:18 CET.
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![SVZ-B (Swiss version of CVX-396) on top of a PRC-77 radio. Photograph via Stiftung HAMFU [2]](img/svzb_prc77_thumb.jpg "image # svzb_prc77_large.jpg")
![SVZ-B (Swiss version of CVX-396) on top of a PRC-77 radio. Photograph via Stiftung HAMFU [2]](img/svzb_prc77_large.jpg)
