Digital Subscriber Voice Terminal
KY-68 is a ruggedized military-grade telephone set with encryption and
decryption facilities, also known as a crypto phone.
It is officially
described as a Digital Subscriber Voice Terminal (DSVT), but is also
called Digital Secure Voice Terminal.
The KY-68 uses the SAVILLE encryption algorithm
and was developed for
the US-Army and Navy in the late 1980s. It was introduced in 1992 
and used until 2008 .
The unit is also known by its National Stock Number (NSN) 5810010828404.
The image on the right shows a typical KY-68 unit, which is significantly
larger than most ordinary phones. The reason for this is the rather large
digital circuitry needed for digital communication and voice encryption,
which is housed in the bottom section of the terminal.
The unit shown here has been demilitarized.
The KY-68 was designed for secure voice communication in combination with
a civil or military switch, using a data rate of 16 or 32 kbit/s.
The unit can also be used in combination with Digital
Non-secure Voice Terminals (DNVT).
In the latter case, a warning tone indicates a non-secure connection.
The tone is issued by the local
switch and stops when the user at the other end picks up the handset.
The KY-68 can also be used for secure communication between two identical
sets that are connected back-to-back.
The price of the KY-68 in 1992 was US$4000. The accompanying HYP-71
power supply unit (PSU) had a price tag of US$1075 .
The KY-68 is currently being replaced by the
Secure Terminal Equipment STE,
which is backwards compatible with the STU-III
but not with the KY-68.
The H-350/U handset is placed in a cradle on the left half of the KY-68.
It connects to the unit by means of an U-283 connector (6-pin version
of the U-229). The handset has a push-to-talk switch (PTT) that is only
used when the unit is operated in half-duplex mode (e.g. over radio).
The hook-switch below the handset (visible in the image on the right)
can be locked by pushing it down and rotating it clockwise. This should be
done when the unit is used in combination with a headset.
The US Navy is known to have used the KY-68 over EHF and SHF radio links.
A light-weight version of the KY-68, called the KY-78,
is available for office use.
Except for the ruggedized case it is identical to the KY-68.
According to some (unconfirmed) reports , the KY-78 (and therefore
also the KY-68) was compromised in the early 1990s. Nevertheless it was
approved for SECRET-classified information. It was still in use in 2008 .
Speech is digitized first using Continuous Variable Slope Delta modulation
(CVSD) with a data rate that is selectable between 16 and 32 kbit/s. This
allows connection to virtually any military digital switch, using digital
(non-secure) voice data. In this mode, it is compatible with the TA-1042
digital non-secure voice terminal (DNVT).
For signaling, it uses conditioned diphase modulation with 8-bit cyclic
permuted code words. This was also used with the Philips Spendex 50
Like the Spendex 50,
the KY-68 uses the GCHQ/NSA-developed Type-1
SAVILLE encryption protocol
for secure voice communication, making it a member of the
of voice encryption devices.
Other devices that are VINSON-compatible are:
VINSON is also used with modern SINCGARS
military radios. Furthermore it is embedded into a number of multi-algorithm COMSEC modules, such as L3 Communications' unityCP custom chip and REDCOM's
HDX-C encryption module. Such COMSEC modules are used as building blocks for
modern cryptographic equipment.
All connections are at the rear of the unit.
The KY-68 can be used in half-duplex or full-duplex mode on virtually
all military communication networks. Most networks, such as the Mobile
Subscriber Equipment system (MSE), require the phone to
be set to 16 kbit/s, whereas the 32 kbit/s mode is used to interface
with the more advanced joint/TRI-TAC switches.
The terminal is suitable for connection to a 4-wire TRI-TAC network, just
like the later STE Tactical phone. One pair of wires
is used for reception. It is connected to the red terminals (RVC) at the
The other pair (black) is used for for transmission (XMT).
The phone can be powered by any voltage from 21 to 56V (DC) and
weights approx. 6.3 kg (14 lbs). A suitable power supply unit, the HYP-71,
can be connected to the socket marked 'PWR',
located below the red line-terminals.
A separate ground terminal is available on the right (GND).
The KY-68 is also suitable for data transmission.
For this, a 55-pin Digital Data Port (DDP)
is available at the rear left. This connector is identical to the
DDP on the TA-1042 Non-Secure Voice Terminal (NSVT).
It allows connection of various digital devices,
such as the Maneuver Control System (MCS)
and the tactical fascimile (AN/UXC-7).
Pin-out of this connector is available
The KY-68 is housed in a sturdy light-weight die-cast aluminium case.
Unfortunately, the unit featured on this page, has been
demilitarized. All of its contents have been removed (not just the crypto
board), leaving the
lower frame empty.
In total, the unit contained 6 circuit boards.
The tamper switches are still in place and are clearly visible in the
One switch is located behind the front panel.
When the front panel is removed, the switch ensures the destruction of
the crypto variables. A similar switch is located
towards the rear. It destroys the crypto keys
when the top section of the phone is removed.
- Static (wire)
- MSRT (mobile)
- Stand-alone (static with RT-1539)
Cryptographic variables (keys) are loaded into the KY-68 by means of
an Electronic Transfer Device (ETD), such as the
or the AN/CYZ-10.
Such ETDs are commonly called key-fill devices or key fillers.
The key filler is connected to the FILL connector on top of the unit.
The key filler can be inserted directly to the FILL connector. It
can also be connected by means of a short 6-way key-filler cable, such
as the one shown here. A total of three key variables can be loaded into
the KY-68. The U and X variables are mandatory. The Function Selector
should be set to the LDU and LDX positions respectively.
The exact initialization procedure is described below.
Optionally, an extra S-variable (SVAR) can be loaded. It provides extra
security between a selected group of users on a per-call basis, or
in point-to-point mode.
'S' means 'Secure'.
A 6.5V mercuric oxide battery
(BA-1372/U or equivalent) is used to
retain the crypto-variables in memory when the unit is disconnected from
its primary power source. The battery is installed
behind a small lid in
the top of the unit, to the right of the FILL connector.
Initialization of the KY-68
- ZEROIZE the unit by putting the VAR STOR switch in the ZERO position.
- Put the VAT STOR switch back in the center position.
- Ensure that the handset is 'on hook' or that the hook switch is locked.
- Set the FUNCTION SELECTOR to DSBL.
- Connect a key filler (e.g. KYK-13) to the FILL connector.
- Set the KYK-13 to 'ON'. Do not press the INITIATE button on the KYK-13.
- Set the FUNCTION SELECTOR on the KY-68 to LDU.
- Select approriate KYK-13 channel (compartment) for U-variable. Ring/Busy and NSW indicator should be lit.
- Move the VAR STOR switch to LOAD (and hold it in position). Parity tone will be sounded.
- Release VAR STOR switch. Tone will be sounded to indicate U-variable is loaded.
- If a 10-second tone is heard (or no tone at all), variable is not properly loaded. Repeat the steps above.
- Load X-variable (using LDX).
- Load SVAR (optional).
The KY-68 has a full numerical keypad
with extra features, similar to other
(digital phones). Apart from the usual 0-9 keys, it has key for R (Red) and
C (white). The four red keys on the right are used for priority override
CConference, end-of-conference, end of dial.
RUsed in certain NET-radio interface calls.
DSBLDisables all operations. Gives master reset to circuits (storage position).
OPOperational mode (normal use)
SVARLoad S-variable and permit 'S'-mode operation
ZEROZEROIZE all crypto variables (pull out and move left, storage position)
LOADInitiate loading of crypto variables (momentarily push right)
Normalhook up/down detection
Lockedpush down and rotate clockwise. Used for headset operation.
PlainPull out for plain text transmission (clear voice).
NSWNon-Secure Warning indicator, flash: non-secure, ON: not initialized.
All connectors on the KY-68 are visible from the rear.
They are used for the following:
FILLConnection of key-filler
EXTDigital Data Port (DDP)
PWRExternal PSU (HYP-71)
RCVReceive terminals (red)
XMTTransmit terminals (black)
Resemblance to the Philips Spendex 50
The KY-68 shows a striking resemblance to the
Spendex 50 military
crypto phone that was developed by Philips Usfa
nearly 10 years earlier for the ZODIAC
integrated communications system used by the Dutch Army.
Most of the controls are in the same position and the technical specifications
are nearly identical. Nevertheless, the Spendex 50 offers several advantages.
The image on the right shows a typical Spendex 50 unit as it was used
by the Dutch Army. Click the image for more information.
Additional features on the Spendex are a red LED display,
a Crypto Ignition Key (CIK), a protected ZERIOSE button and the ability
to enter a key manually.
It is extremely well protected against EMP strikes.
Furthermore, the Spendex 50 uses a patented system for storing
distributed key-pairs, called Key-Cube key. Like with the KY-68, the
key variables are loaded using a standard
key transfer device
such as the KYK-13 (or similar).
The Spendex 50 was known within the Dutch Army as Digitaal Beveiligd
Telefoontoestel (DBT). It was introduced in the early 1980s and was
used until the early 2000s,
was phased out in favour of the
new TITAAN system.
The Spendex 50
was approved for use by NATO.
- TM 11-5810-329-10
Operator's Manual KY-68 and HYP-71.
- TM 11-5810-239-23
Organizational and DS Maintenance for KY-68 and HYP-71.
- TM 11-5810-329-24P
Organizational DS and GS Repair parts and Special Tools List KY-68 and HYP-71.
- KAO 193A/TSEC
Guidelines for the Use and Operation of TRI-TAC COMSET Equipment (Confidential).
- KAM 403/TSEC
KY-68 Limited Maintenance Manual (Confidential).
- KAM 404/TSEC
KY-68 Full Maintenance Manual (Secret).
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