Military grade portable cipher machine
Picoflex is a field-grade portable electronic cipher machine
introduced in 1982 by Philips Usfa in Eindhoven (Netherlands),
developed in cooperation with AEG Telefunken
in Backnang (Germany). The device uses the classified NATO-approved
CEROFF cryptographic algorithm, developed by Philips for the
highly successful Aroflex cipher machine,
and is crypto-compatible with
Aroflex and RACE (KL-51).
The device is also known as UA-8035 and as ANT Telekrypt-Mini .
A civil variant is known as Miniflex.
Picoflex is a compact light-weight field-grade off-line encryption/decryption
device for written messages. The encrypted text is formatted into
containing only the 26 letters of the Latin alphabet and no
The 2000 character memory can hold one crypto message for transmission and
an unlimited number of messages for decryption at the same time, subject,
of course, to available memory.
Text can simply be written down or transmitted by voice,
over normal PSTN telephone lines or via radio connections.
The image above shows a typical Picoflex unit seated on a desk with a
printer, a modem and an acoustic coupler for transmission of messages
via a standard telephone line (PSTN).
To the left of the Picoflex, a ruggedized thermal printer
is attached. It replaced the Miniflex printer
that did not meet NATO requirements.
To the right of the main unit is a (radio) modem made by Telefunken.
To protect it against dust and rain, the keyboard was originally covered
by a transparent silicone sheet, but as this
silicone sheet became opaque and brittle
over the years, it was subsequently removed from most units.
It has also been removed from the unit shown here.
The diagram below shows the main Picoflex unit (centre) with the military-grade
thermal printer (left) and ditto modem (right). The acoustic coupler is
connected to the socket marked Radio / Phone at the top right. This socket can
also be used for connecting the device to a radio set. In the latter case,
a handset can be connected to the Handset-socket. The device shown here
is battery powered. Alternatively it could be powered by a drop-in
power supply unit (PSU).
The device is switched on by setting the power switch (to the right of the
battery compartment) to ON. If a printout is required, the printer should also
be turned ON.
The main unit can be used as a stand-alone device for manual
input and read-only output.
The speed of operation can be enhanced by the addition of one
or more installable options:
These options allowed the machine to be be used over the available communication
channels and allowed messages to be printed out as plain text.
As Picoflex was a military device, it was delivered in NATO olive-green,
housed inside a ruggedized green carrying case.
The accessories (i.e. the printer, the
acoustic coupler and the radio modem) were also painted green.
Please refer to the
Miniflex Operating Instructions
for an overview of the additional modules.
For use by the Army, Picoflex was often built into a sturdy
military-grade briefcase, such as the one shown below. The machine had built-in
batteries and was built into the case together with some of its accessories,
in such a way that it could be operated directly from within the case.
The image on the right shows a typical Picoflex setup, built into a standard
green aluminium military briefcase, together with some common
accessories and a range of supplies.
The main Picoflex unit is mounted at the center with
a printer (left) and
modem (right) bolted onto it.
Both the main unit and the printer can be
powered by the internal batteries. The modem is always powered by the main
unit. The entire setup can also be used with an
external power supply unit (optional),
that plugs straight into the battery compartment (see below).
Behind the main unit is an acoustic coupler
that allows data to be sent via a normal analogue telephone set.
To the left of the coupler are two black zipper-bags that are used to store the accessories and supplies,
such as the external power supply unit and spare
thermal print rolls.
The main Picoflex unit is a completely stand-alone device that is housed in
a die-cast aluminium case, designed by Telefunken. Telefunken also designed
the keyboard, the display, the battery compartment and the external power
adapter. In other words: they designed the exterior, whilst Philips
developed the interior, consisting of two large PCBs and a crypto-unit.
The image on the right shows a typical Picoflex main unit, with a
keyboard consisting of the standard
alpha-numerical keys, plus some punctuation marks and a spacebar.
At the top row is a series of red and green function keys.
Initially, all Picoflex units were supplied with a
protecting the keyboard, but these foils became
brittle and white
The unit can be used on its own, when it is powered by the
5 AA-size penlight batteries
in the compartment to the right of the display.
At the upper right corner is the power switch.
The unit has two connectors: one at its left side and one on the right.
The one on the left side is used for the connection of the
present), whilst the one on the right can be used for the connection of
an acoustic coupler.
It can also be used for connection of a radio modem,
in which case the acoustic coupler is connected to the
modem instead. When used over radio, an optional handset can be connected
to the modem as well, to allow a voice conversation en-clear before
initiating a crypto transmission.
A miniature thermal printer can be connected directly to the left side
of the Picoflex. Initially, Philips wanted to use the same printer as the
one used with Miniflex.
Although that printer has
extra shielding to prevent unwanted emission of data, it was not suffient for
military TEMPEST requirements. As a result,
designed an improved TEMPEST-shielded case for it.
The image on the right shows a typical Picoflex printer in a Telefunken-designed
case, that is milled-out of a solid piece of aluminium. A red switch in the
upper right corner of the printer case, ensured that the printer was switched
off whenever the lid was opened.
The printer is fed with small 35 mm wide silver-coloured thermal paper rolls.
Each line can take 14 characters, defined in a 7 x 5 pixel matrix.
Encrypted text is printed in two 5-letter groups per line.
When printing, the paper stays inside the case, but can be read
through a window.
When in operation, the head of a thermal printer uses high-peak currents
in order to print pixels onto paper.
Although the case is 'draft-free' from an HF point of view,
high-energy pulses like these can cause information to 'leak' away via
the power lines. To prevent this, the printer can only be
powered by an internal battery and not, like Picoflex itself, by an
external power supply.
For transmission of encrypted messages over radio links, Picoflex could
be connected to a military radio set, by using the optional radio modem.
Two different versions of the radio modem exist. The one initially developed
by Philips was also available for the Miniflex.
As it was not suffiently shielded for military applications, Telefunken
developed a slightly larger modem, with better
TEMPEST shielding and additional filters between connectors
and electronic circuits.
The image on the right shows the improved Telefunken radio modem.
Like the original modem it can be bolted directly to the right side of
the Picoflex main unit. Power is derrived from the main unit, via the
15-way sub-D connector.
The modem also allows the acoustic coupler to be connected. For this
purpose, the connector RADIO/PHONE at the rear of the modem is used and the
middle switch at the right should be set to PHONE.
When using Picoflex via radio, a suitable radio set should be connected to
that connector whilst the switch is set to RADIO.
When using Picoflex over radio, the encrypted message is sent as a series
of tones via a standard audio (voice) channel. Picoflex can therefore be
connected directly to the microphone input of the transmitter.
In order to allow the operator to initiate the call en-clear in speech
mode, a standard military handset can be connector to the HANDSET socket
at the rear of the modem.
In order to send and receive encrypted messages over standard (analogue)
telephone lines, most Picoflex units are equipped with an external
acoustic coupler. The coupler connects either directly to the right side
of the Picoflex (using a 15-way sub-D connector), or via the radio modem
(using a military connector), like on the machine shown here.
The image on the right shows a typical acoustic coupler for the Picoflex.
The unit is identical to the one supplied with Miniflex.
It allows the handset of a standard telephone set (of the era) to be mated
with the coupler.
During a session, the handset is kept in place by a firm rubber strap at
the center. Two sturdy rubber cuffs should prevent audio (speech) from
leaking into the handset. Although the two rubber cuffs can be adjusted
somewhat, the coupler was typically meant for handsets like the one
shown in the images below.
The acoustic coupler shown here, has a military audio connector to the
end of the curly cable, allowing it to be connected to the RADIO/PHONE
socket of the modem. The rightmost images below show a
from Philips Usfa  with an acoustic coupler that is connected directly
to the right side of the Picoflex, instead of the modem.
Picoflex can be powered internally by placing five AA-size cells inside the
battery compartment on the top face of the unit. It can also be powered
externally by removing the entire battery compartment and replacing it with
an external power supply unit (PSU), such as this one.
The image on the right shows the special (optional) power adapter.
It consists of a standard mains voltage adapter, a filter and
a special plug
in the shape of a battery pack.
The external PSU is connected by removing
the existing battery
pack and placing the plug-end
of the PSU in the empty battery compartment.
The black adapter can then be connected to the mains
The filter is present in order to prevent unwanted information leakage
via the mains. Inside the green filter block
is a Siemens mains filter.
Development of the Picoflex started in 1976.
It was intended as miniature cryptographic device for portable and field
It was also aimed at possible NATO
evaluations such as MERCS
(also known as MERSEX) and CALL SIGN.
was Philips' partner in this project. They developed
the keyboard, the printer and the modem, and
also carried part of the (financial) risk.
The device would be small enough to be fitted inside a standard
briefcase and had a built-in paper strip printer. The image on the
right shows an artist's impression  of the first prototype of
PICOFLEX, that was also present in the (never published)
sales brochure of 1976 .
Initially, the enclosure of the Picoflex was designed by AEG daughter
Olympia, but the project was stopped when the case was found inadequate
and too expensive .
The MERCS evaluation was later won by the
Norwegian PACE crypto device,
built by Lehmkuhl (Kongsberg).
In 1978, the project was restarted in the light of new NATO requirements.
The specifications were altered, the Aroflex algorithm was used
and Telefunken designed a new case.
Development was finished in 1982 and Picoflex went into production,
albeit in lower quantities than anticipated.
Including the civil Miniflex variant, over 300 units had been produced
by the end of 1982 .
Like Miniflex, Picoflex was a co-development of
Philips Usfa (Netherlands) and
AEG Telefunken (Germany).
Telefunken produced the die-cast aluminium case, the keyboard, the display
and the power supply unit (PSU), whilst Philips designed and built the CPU
and the crypto module.
In the Netherlands, Picoflex was sold under the Philips brand, whilst Telefunken
took care of the German market. Telefunken later moved their sales to
(Later: ANT Bosch GmbH, now: Selex GmbH) which they partially owned at the time (51%).
It is therefore possible to find
Picoflex units with either the Philips, Telefunken or ANT logo on it.
In the 1986 edition of Jane's Military Communication
it was offered by ANT as the Telekrypt-Mini. The article states that the
Telekrypt-Mini was introduced in 1980 at a (starting) price of USD 7000 .
Although the physical dimensions and case of the Picoflex are identical
to those of the Miniflex,
the internals of the Picoflex, and hence the cryptographic algorithm,
are completely different.
Whilst the cryptographic algorithm of Miniflex is implemented in software,
Picoflex has a secret potted crypto heart with a hardware-based algorithm.
This crypto heart is built around a complex ASIC-based hardware circuit,
that contains the NATO-approved Aroflex CEROFF crypto algorithm,
making it crypto-compatible with similar systems like
and RACE (KL-51).
In order to protect Picoflex against eavesdroppers, great care was
taken to ensure that the unit was TEMPEST proof.
The case is well protected against unwanted emission of
power and signals that otherwise be exploited by an interceptor
to recover the original clear text of a message.
The transparent parts of the display and the printer,
contain a metal grid that helps shielding these signals.
In practice, the original thermal printer caused some problems as it produces
high-energy current peaks.
Although the level of shielding was sufficient for civil
applications, the enclosure of the printer was later replaced by a
better Telefunken-designed alternative.
The Picoflex is known under the following names and designators:
4322 082 08600Processor board (with confidential crypto heart)
4322 082 09850Crypto board
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© Crypto Museum. Created: Tuesday 06 March 2012. Last changed: Wednesday, 08 February 2023 - 08:14 CET.