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EMU Yugo ← KzU-42
Electronic message encryptor
KzU-44 is a stand-alone digital
handheld encryption device,
developed around 1991 by Institut Mihaljo Pupin in Beograd
(Belgrade, Serbia); at that time the capital of
Yugoslavia. 1
Like its predecessor – KzU-42 –
it was used
by the Yugoslav National Army (JNA)
during the Yugoslav Wars (1991-2001)
for handling
text messages (telegrams) which were sent by courier,
morse code,
telegraphy (teleprinter) or
verbally via radio
or telephone.
Also known as 3215-1084-1511.
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The device is housed in an extruded aluminium enclosure that
measures 152 x 89 x 30 mm and weights 310 grams (without
the batteries). It has an alphanumeric keyboard with 42 buttons,
and a slightly raised 1 × 16-character (LCD) display.
It is powered by
four internal AA-size batteries.
Up to four cryptographic keys can be stored in the internal
memory, each of which consists of 40 characters, using only
the letters A to P. The first 5 characters of the key is
a check group and is sent in clear at the beginning of an
encrypted message. It allows the recipient to verify the key.
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According to the original checklist that came with the device,
it was supplied without operating instructions or a user manual. Instead the
instructions were supplied directly to the user, as per secret order
VP 4578-Beograd. This was probably done for security reasons.
Fortunately, the device shown here was found with a brief instruction
sheet that explains the basic operation.
It has serial number 92 06 0378 and was issued
on 26 June 1992. It was partly built in 1991 [1].
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Beograd (Belgrade) was the capital of Yugoslavia from its creation in 1918
to its dissolution in 2006. Yugoslavia itself had already collapsed in 1992.
Belgrade is currently the capital of Serbia [2].
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The KzU-44 can hold up to four different keys, numbered
1 - 4. Each key consists of 40 letters, entered as
8 groups of 5 characters each. This first 5-letter group
is the check group and is not actually part of the key.
It is used by the recipient to verify whether the correct
key is used. Note that only the letters A - P can be used
for the key. Trying to enter other characters will raise
an error. The table below gives some examples of the keys
we have used when testing our KzU-44.
# Check ------------------ key ------------------
001 AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA
002 AAAAB CCCCC CCCCC CCCCC CCCCC CCCCC CCCCC CCCCC
003 AAAAB ABCDE FGHIJ KLMNO ABCDE FGHIJ KLMNO PPPPP
004 AAAAC ABPOF KAEID PCFAH BBONA MCADM HGDEI LCDIA
Only the last 7 groups (35 letters) are used for the key.
As only the letters A-P can be used for the key (16 possibilities),
each letter represents 4 key bits, which gives a total of 140 key bits.
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When not in use, the KzU-44 can be protected against dust, moisture
and dirt by stowing it in the supplied Tb-112 artificial leather
storage case or wallet. Checklist and
short instructions were usually included in the wallet.
The wallet does not offer space for cables and spare batteries.
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The actual KzU-44 encryptor resembles a pocket calculator of the era.
It measures 30 x 89 x 152 mm and weights 310 grams. The device has a
full alphanumeric keyboard with 10 keys for the numbers (0-9), 26 keys
for the letters (A-Z) and 6 function keys. Their functions are
listed below.
The unit is powered by four 1.5V AA-size batteries that are installed
internally. It has a serial port for connection to external (computer)
equipment or a modem.
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The checklist shows the release date
(25 June 1992 in this case) and lists the items that were delivered.
The KzU-44 encryptor and the Tb-112 carrying case
were part of the delivery, but the operating
instructions were missing, as per secret order
VP 4578-Beograd.
The checklist is printed at DIN A5 size and folded to A6 size,
so that it fits inside the wallet.
It also serves as a logbook or passport for any aftermarket
modifications or repairs.
➤ Download checklist
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Although the operating instructions were not included with the
device, the one shown here came with an instruction sheet
that explains how to enter, encrypt and decrypt a message.
The instruction sheet is printed at DIN A4 size (double sided)
and folded to A6 size so that it fits inside the wallet.
The supervisor password (POT-986) is handwritten in the left margin.
➤ Download instruction sheet
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Operating the KzU-44 is straightforward. The keyboard consists of
42 keys: 36 white ones for the letters (A-Z) and the number (0-9),
and 6 black function keys. The upper function key (UK) is the power
button. Pressing it turns the device on. Pressing it again turns
the device off. The other black keys are explained
in the table below. The middle four keys have a double function.
They can be used by themselves (e.g. SPACE) or in combination with
the shift key ↑ (e.g. ENTER).
After turning the device on with the (UK) button, it will ask
for the password (UNESI LOZINKU !). Enter the password (POT-986)
and press ENTER. The display now shows UNESI KOMMANDU ?
(enter command). You may now enter any of the two-letter
commands from the table below.
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MNE
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Description
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BS
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Delete input and output buffers
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DS
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Decipher numbers or words
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GN
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Generate pseudorandom string
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IK
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Change valid key at power cycle
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IT
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Text correction
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PL
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Change operator and supervisior password
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PI
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Show contents of output buffer on display
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PO
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Help (show mnemonics and function names)
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SB
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Encrypt into numbers
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SS
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Encrypt into text
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TS
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Test device
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UK
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Enter internal key
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UZ
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Enter characters in the input buffer
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Display
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English
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Description
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UNESI LOZINKU !
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Enter password
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e.g.: POT-986
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UNESI KOMANDU ?
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Enter command
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Mnemonic, e.g. UZ
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OPER/PRETP (O/P)
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Operator/Supervisor
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e.g.: O
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ST/OT (S/O)
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Enter ciphertext or plaintext
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e.g.: O
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ST
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Šifrirani tekst (ciphertext)
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OT
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Otvoreni Tekst (plaintext)
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NEISPRAVAN KLJUC
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Faulty key
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PRAZAN BAFER
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Empty buffer
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Below is an example of a simple text (THIS IS A TEST) that is
encrypted with a key that consists of 40 x 'A'. In this case,
the ciphertext consists of seven 5-letter groups, which is longer
than the original plaintext. This is because the ciphertext also
contains the check group (AAAAA) and a unique (machine-generated)
message key.
As a result, the ciphertext will be different each
time, even when the plaintext and the key haven't changed.
Furthermore, the message may contain letters and numbers,
whilst the ciphertext consists of letters (or numbers) only.
For example:
Plaintext: THIS IS A TEST
Key 001: AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA
Encrypted: AAAAA FCOAK OGIEN OIPHK UJGFV BKYNK CPWRX
When decyrpting the text, the full ciphertext has to be entered,
including the check group (AAAAA in this case). Once it is complete,
press Enter followed by the DS command. This will decrypt the
ciphertext. Then use the PI command to reveal the decrypted text.
Plaintext: THIS IS A TEST
In the above example, the ciphertext consists of the letters (A-Z).
This was achieved by using the SS command to encrypt the plaintext.
Alternatively, the plaintext can be encrypted into a numeric ciphertext
by using the command SB. The same message might now be something like this:
Numeric: 00000 52602 51550 23112 56601 13304 08773 70499 95153
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Alternatively, the interior can be extracted by
unlocking the case shell (with a pen) and sliding it further towards
the rear until it comes off.
This reveals the electronic circuits as shown in the image on the right.
At the bottom are the keyboard and the display, which are mounted onto a
large printed circuit board (PCB). At the
other side of the PCB is the battery compartment and a smaller PCB —
the central processing unit or CPU.
The latter is held in place by four 10 mm spacers at the corners, and is
connected to the keyboard PCB by means of two headers (K1, K2).
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After removing the screws from the spacers,
the the CPU board can be
extracted from the larger PCB.
The CPU is built around a
CDP1802 8-bit microprocessor
with an external 8KB static RAM to hold the messages,
and a 32KB EPROM that holds the firmware [a][3].
According to the date codes on the various components,
the device shown here was built in 1991 or shortly thereafter.
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Device Portable text encryptor Model KzU-44 Designator 3215-1084-1511 Manufacturer Institut Mihaljo Pupin (Belgrade, Serbia) User Yugoslav National Army (JNA) Year 1991/92 Conflict Yugoslav Wars (1991-2001) Keys 4 Key length 40 characters (8 groups of 5 letters) A-P only Key strength 2140 (140 bits) Power 6V Batteries 4 x 1.5V AA-size (penlight) Password POT 986 Dimensions 152 x 89 x 30 mm Weight 310 grams (without batteries)
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© Crypto Museum. Created: Thursday 23 September 2021. Last changed: Friday, 13 May 2022 - 19:38 CET.
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