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TRW
The image on the right shows a KL-43C, as it was used by NATO.
The device is housed in a rugged watertight die-cast aluminium enclosure which
measures 43 × 170 × 95 mm and weighs 814 grams, batteries not included.
It has a wide 2 × 40 character Liquid Crystal Display (LCD) and a keyboard
with 59 tactile rubber buttons.
The device is powered by four 1.5V AA-size (penlight) batteries that
are installed behind a sealed door at the left side. At the right side is a
standard 6-pin U-229-like connector for connection to a radio
or an optional thermal printer.
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At the bottom is a watertight acoustic adapter that provides access
to the built-in 300 baud modem, that can be used as an alternative to
a directly wired radio. It has to be held against the microphone or speaker
of the radio's handset. The acoustic adapter also provides the key-clicks
when operating the keyboard. In silent mode all key-clicks and
other sounds are muted.
Known as AutoManual System, the KL-43C was first fielded with the US
Armed Forces in 1990 [7].
In 1995 it was succeeded by the slightly improved KL-43F, which offers
support for a second language (French).
The entire KL-43 family was declared obsolete in May 2013 [5].
According to some sources, the Datotek XMP-500 is the export version
of the KL-43 [6]. Instead of the secret proprietary NSA algorithm, the
XMP-500 uses 56-bit DES, but is key compatible with the KL-43.
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PLEASE HELP —
We are still looking for valid keys for the KL-43C, so that we will
be able to demonstrate this unit. If you hve a valid (test) key set,
or if you have information about the format of the key set, please
contact us.
KL-43 Initial design KL-43A Early version KL-43C Tactical ruggedized version KL-43D Regular version with small keyboard KL-43E High-volume version with full-size keyboard
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KL-43F Similar to KL-43C KL-43G Similar to KL-43D KL-43H Similar to KL-43E
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The image below provides an overview of the features of the KL-43C —
the version that was used by the US Army and NATO.
It is fully self-contained, and is powered by four 1.5V AA-size alkaline
batteries that are installed behind a hinged sealed access door at
the left side. The device is powered ON by pressing the SRCH button
at the top right, followed by 'Y' (yes). This briefly displays a copyright
message and software version number. The device featured here shows
the message:
TRW EPI Inc. (C) 1984-92
KL-43C software version 1.6.9
According to the label at the bottom of the unit, the device
featured here was manufactured in the second quarter of 1991,
whereas, according to the startup message above,
the firmware was released in 1992. This means
that the firmware was updated at least once in its lifetime.
This was done by replacing the ROM (i.e. the CCI chip U-ATA),
and is confirmed by traces on the PCB.
The right side of the device holds a standard U-229 connector
with an analogue audio interface. It allows the KL-43C to communicate
via to the voice circuit of a (military) radio set.
The U-229 connector also holds an asynchronous digital interface
(RS232) for connection of a printer.
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At the bottom of the device (not visible here) is the acoustic coupler
that allows the modem tones to be played before the microphone of a
handset. It also produces the key-clicks when operating the keyboard.
When receiving a message, the acoustic coupler should be held against
the speaker part of the handset.
The acoustic coupler allows the device to be used with non-standard radios.
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The KL-43C has 16 compartments for storing encryption keys, numbered
01-16. The display shows 4 compartments at a time (e.g. 01-04).
Use the ∧ and ∨ buttons to scroll through the available compartments.
A key compartment uses the format 01-AVAILABLE-00 , where 01
is the compartment number, AVAILABLE is the key name, and 00
is the key update level.
When first powering the device, all key compartments are empty (AVAILABLE)
and the display contrast is set to maximum. It may therefore be
difficult to alter the viewing angle of the display. However,
before the viewing angle can be changed, the user first has to
enter at least one valid key set. When entering a key, first select
the desired compartment, e.g. 01 , then enter a suitable name,
e.g. TEST , followed by ENTER. The KL-43C will now briefly
show the key name. Then enter the key, which is divided into 4 key sets.
Each set consists of 8 letters (A-Z).
Enter the first key set and press ENTER when complete. Use DCH to
correct mistakes. Then enter the remaining key sets. When all key sets
have been entered, the KL-43C checks whether the key is valid. If it is
not a valid key, it will display the text: Key is Invalid .
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At present, the format of the keys is unknown. It is likely though,
that the key length is 128 bits, assuming that each of the 32 key
characters (A-Z) represents 4 data bits. It is also likely that the
last 8 bits are used as a checksum, in a similar vain as a
SAVILLE key. It is unclear however, how the 26
characters of the Latin alphabet are mapped onto the corresponding
4-bit values. If you know more about the format of the KL-43C keys,
please contact us.
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BOT
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Beginning of text
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EOT
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End of text
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∨
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Down
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∧
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Up
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<
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Left
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>
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Right
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BOL
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Beginning of line
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EOL
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End of line
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D CH
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Delete Character to the left of the cursor
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D WD
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Delete word to the right of the cursor
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SRCH
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Search (power on)
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ZRO
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Zeroize
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XIT
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Exit (back to main menu)
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CLK
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Clock
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SPC
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Space
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The KL-43C was supplied in a canvas carrying bag with
camouflage colours, such as the one shown in the image on
the right. It has separate compartments for the KL-43C, the
operating instructions and the (tailor made) radio cable.
The bag can be carried from the shoulder, but can also be
attached to the soldier's webbing.
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The image on the right shows the bare KL-43C terminal that is
housed in a rugged green die-cast aluminium enclosure. It measures
just 168 × 95 × 43 mm, and was the smallest of the KL-43 models.
Without batteries it weighs 814 g.
Alkaline batteries are good for 24 hours of uninterrupted use.
Rechargeable NiCd batteries last approx. 8 hours.
At the right is a standard U-229 radio connector.
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The KL-43C is connected to a suitable radio via the
6-pin U-229 connector at the right side. This connector
is wired according to the
international U-229 specification.
In the Netherlands, the device was supplied with the
CX-4643 twin-radio cable shown in the image on the right.
This cable has two radio connectors: one for the RT-3600
and one for the RT-4600 radio (which
are wired differently).
In transit, the cable can be stowed in the front compartment
of the canvas carrying bag.
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The KL-43C was supplied with the original operating instructions
provided by TRW. The one shown here is revision F, issued on
15 August 1991 (P/N 410-308-1). As the KL-43C featured here was
used in the Netherlands, the front page is covered by a self-adhesive
label in Dutch.
Also supplied in the Netherlands was a folded 6-page yellow
Quick Reference Chart at DIN A6 size, that provides instructions
for connecting and using the device (in Dutch).
➤ Operating instructions (English)
➤ Quick Reference Chart IK004164 (in Dutch)
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The KL-43C is housed in a die-cast aluminium enclosure that consists
of a bottom part – the case shell – that holds the electronics and
the batteries, and a top part that holds the keyboard and the liquid
crystal display (LCD). The interior can be accessed by removing
13 recessed hex screws from the rear side of
the front panel. Note that these screws are protected by a silicone sealing.
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After the 13
screws have been removed from the top panel,
the top (with keyboard and LCD) can be separated
from the bottom. This has to be done carefully, as the top panel
is connected to the printed circuit board (PCB) in the bottom part,
by means of two short flex wiring strips.
The image on the right shows the interior after the top panel has
been separated from the bottom part. The two flex wiring strips
are clearly visible at the left. The white paper-based strip
connects the keyboard to the main PCB. Partly hidden behind it,
is a shorter mylar-based one.
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It connects the LCD to the main PCB. Note that both wiring strips
are soldered at both ends.
Treat the wiring strips carefully, as they cannot be removed and are
very fragile — especially the white paper-based one — which we noticed
when taking the device apart to photograph the interior.
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The top part consists of two die-cast frames that are bolted together.
The outer part holds the keyboard (not visible here), whilst the inner
part holds the display (the electronics are visible).
The bottom part of the case holds two PCBs:
the main board with the processor, and an
interface board which is covered by a metal
panel. The interface board holds several relays, and is connected
to the main PCB by means of four feedthrough filters.
The main PCB, shown in the image on the right, holds a NSC800
microprocessor — a military grade variant of the Z80 [a].
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Also present is an NSC858 UART [b], which provides a serial port that is
available on the U-229 connector. At the top left is a chip marked
CCI U-ATA, which is the ROM that holds the software (firmware). Immediately
below it is a CXK58257 CMOS RAM that holds the messages and the encryption
keys. Its contents are retained by a 3.5V Lithium battery
at the bottom centre. To the right of the CCI chip is a
RICOH RP5C15 Real-Time Clock (RTC) that maintains the current time.
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It works in conjunction with the narrow 32 kHz quartz crystal at its bottom right,
and is powered by the 3.5V Lithium battery, so that the RTC is kept running
when the device is switched off.
The built-in acoustic coupler is built around a 74HC943 300 baud modem
that is located below the UART. It has its own 3.570545 MHz crystal
from which the baud timings are derived, plus an LM386 audio amplifier
that drives the speaker.
The main PCB of the device featured here, is revision F, and has three
white modification wires.
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When taking a closer look at the top left corner of the main PCB
is becomes clear that the board was reworked at least once in its lifetime.
The ROM in the top left corner (marked CCI U-ATA) was replaced with
a newer version of the firmware, probably in 1992, a year after its
production. The PCB wasn't cleaned afterwards and the flux residues
are still visible at both sides of the board.
It is also likely that the 3.5V Lithium battery
was replaced at least once.
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When we opened the device in April 2026 to photograph the interior, we noticed that the
3.5 Lithium battery — needed to retain the settings and the
keys — was flat after 35 years.
As the original Keeper LTC-7PN is rather expensive (USD 54 to USD 76), we decided to
order a drop-in replacement from another manufacturer. Such batteries are available
on the internet for ~ USD 15.
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The battery is soldered in place and was thought to last for the economic
lifetime of the device, which was approx. 10 years. For this reason it
was considered not te be a user serviceable part.
If we want to be able to demonstrate the KL-43C in the years to come,
it is necessary to replace it.
Battery ordered. Currently awaiting delivery.
To be continued...
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After closing the device and testing it, it didn't come alive again.
Although we are always extremely careful when accessing the interior
of an historical cipher machine, it looked like we had broken one of
the interal wires in the course of opening and closing the aluminium enclosure.
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After reopening the enclosure and inspecting the internal wiring,
it was noted that the paper-based wiring strip from the PCB
to the keyboard had a suspicious fold, just above the soldering
pads on the PCB. The fold, which is visible in the image on the right,
was clearly not caused by ourselves, but more likely during assembly
in 1991 or when the ROM was replaced in 1992.
Paper-based flex wiring is not recommended for military
applications, and is a weak point in the design of the KL-43C.
It would have been better to use mylar-based flex wiring like on the LCD.
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As a temporary solution, a teflon bypass wire was soldered in parallel with
the leftmost wire of the flex strip, to prove that this was indeed the cause
of the malfunction. With the wire in place,
the device powered up normally after pressing the SRCH button.
Currently awaiting rewiring of the entire flex strip. To be continued...
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The KL-43C and KL-43F have a standard US/NATO 6-pin audio connector,
which is also known as U/329 or U-229. It allows the device to be
connected to a radio or to a printer.
Below is the pinout when looking into the connector.
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GND Ground AFI Audio into KL-43 (10-350 mW, 1200Ω) PTT Push-to-Talk (connects to GND) AFO Audio from KL-43 (20 mW, 134Ω) RXD Data into KL-43 (or CTS from printer) TXD Data from KL-43 (or Data to printer at 1200 baud)
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The KL-43D, E, G and H have a 5-pin 180° DIN socket for connection
of an acoustic coupler or a radio. Below is the pinout when looking
into the socket.
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AFI Audio to KL-43 (-3dBm to -5 dBm, 4kΩ) GND Ground AFO Audio from KL-43 (-9 dBm, 200 mV, 8Ω) GND Ground GND Ground
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KL-43D, E, G and H can be connected directly to an analogue telephone line
(PSTN) via the RJ-14 modular jack socket marked LINE. An extra RJ-14 socket
is available for connection of the existing telephone set (PHONE). Below is
the pinout when looking into the LINE socket.
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- unused P5 Connected to pin 5 of the PHONE jack RING 2-wire 600Ω balanced line TIP 2-wire 600Ω balanced line P2 Connected to pin 2 of the PHONE jack - unused
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STR STROBE D0 Data bit 0 D1 Data bit 2 D2 Data bit 3 D0 Data bit 4 D4 Data bit 5 D5 Data bit 6 D6 Data bit 7 D7 Data bit 7 - unused BUSY Printer busy - unused - unused - unused - unused - unused - unused - unused
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GND Ground GND Ground GND Ground GND Ground GND Ground GND Ground GND Ground GND Ground GND Ground GND Ground GND Ground GND Ground INIT Initialize - unused GND Ground - unused - unused - unused
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Model KL-43C01, TSEC/KL-43C Part No 410-320 Manufacturer TRW, Colorado Electronics Corp. LLC Year 1987 Fielded 1990 NSN 5810-01-289-7322 (TRW), 5810-01-318-0414 (CEC) Languages English Message 2 × 2600 characters Connections U-229 Data RS232 (via U-229), 300, 1200, 4800 or 9600 baud Modem Acoustic (built-in), 300 baud, Bell-103, simplex Speed 50, 75, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud async. 1 Sync time 750 ms (400 ms for versions ≤ 1.7.0) Printer TP-40S via Serial I/O 1200 baud (U-229) Power 4 × AA-size Alkaline or NiCd battery Duration 24 hours (8 hours with NiCd) External - Standards NACSIM 5100A TEMPEST, MIL-STD-461 (A1b, A3, A4), MIL-STD-810. Enclosure Ruggedized die-cast aluminium Temperature -2°C to +50°C Storage -40°C to +65°C Humidity 100% Dimensions 168 × 95 × 43 mm (HWD) Weight 814 g (without batteries) Cost ?
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Meets RS232C standard, except for risetime at 9600 and 19200 baud.
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Model KL-43D Manufacturer TRW Year ? NSN 5810-01-318-0415 Languages English Message 1 × 2600 characters Connections DIN, RJ14 Data Optional external adapter (300 baud) Acoustic External adapter (via DIN socket) Printer TP-40P via Parallel I/O (D-36) Power 4 × AA-size Alkaline or NiCd battery Duration 24 hours (8 hours with NiCd) External 12V DC adapter Standards FCC par 15 leel A Dimensions 267 × 140 × 38 Weight 800 g Cost USD 300 [4]
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Model KL-43E Manufacturer TRW Year ? Languages English Message 1 × 2600 characters Connections DIN, RJ14 Data Optional external adapter (300 baud) Acoustic External adapter (via DIN socket) Printer TP-40P via Parallel I/O (D-36) Power 4 × C-size Alkaline or NiCd battery Duration 72 hours (24 hours with NiCd) External 12V DC adapter Standards FCC par 15 leel A Dimensions 260 × 235 × 51 Weight 1400 g Cost USD 1000 [4]
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Model KL-43F Manufacturer EPI Year 1995 NSN 5810-01-376-7375, 5810-01-387-1642 Languages English, French Message 2 × 2600 characters Connections U-229 Data RS232 (via U-229) Acoustic Built-in Speed 50, 75, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud async. 1 Sync time 750 ms Printer TP-40S via Serial I/O 1200 baud (U-229) Power 4 × AA-size Alkaline or NiCd battery External - Duration 24 hours (8 hours with NiCd) Standards NACSIM 5100A TEMPEST, MIL-STD-461 (A1b, A3, A4), MIL-STD-810. Enclosure Ruggedized die-cast aluminium Dimensions 168 × 95 × 43 mm Weight 900 g Cost ?
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Meets RS232C standard, except for risetime at 9600 and 19200 baud.
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Model KL-43G Manufacturer EPI Year ? Languages English Message 1 × 2600 characters Connections DIN, RJ14 Data Optional external adapter (300 baud) Acoustic External adapter (via DIN socket) Printer TP-40P via Parallel I/O (D-36) Power 4 × AA-size Alkaline or NiCd battery Duration 24 hours (8 hours with NiCd) External 12V DC adapter Standards FCC par 15 leel A Dimensions 267 × 140 × 38 Weight 800 g Cost ?
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Model KL-43H Manufacturer EPI Year 1990 Languages English Message 1 × 2600 characters Connections DIN, RJ14 Data Optional external adapter (300 baud) Acoustic External adapter (via DIN socket) Printer TP-40P via Parallel I/O (D-36) Power 4 × C-size Alkaline or NiCd battery Duration 72 hours (24 hours with NiCd) External 12V DC adapter Standards FCC par 15 leel A Dimensions 260 × 235 × 51 Weight 1400 g Cost ?
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Obtained from Jerry Proc in May 2025 [1].
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- Jerry Proc and contributors, KL-43 Automanual Equipment
Jerry Proc's Crypto Pages.
Visited 30 May 2025.
- Wikipedia, KL-43
Visited 30 May 2025.
- NATO, NCI Agency, KL-43F 1
NATO Information Assurance. Visited 2 June 2025.
- Lt. Col. David M. Fiedler, The KL-43: burst communication on a budget
Winter/Spring 1990. pp. 42-47.
- DIN Digest, May 2013
UK Department of Defense, May 2013.
- Jerry Proc, Datotek XMP-500
9 April 2013.
- C4IEW and Sensors Project Book, Fiscal Year 1996
US Army, 23 May 1996. Page 36-13.
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© Crypto Museum. Created: Monday 02 June 2025. Last changed: Sunday, 12 April 2026 - 07:35 CET.
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