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Picoflex   UA-8035
Military grade portable cipher machine

Picoflex is an electronic cipher machine developed by Philips Usfa between 1976 and 1982 in co-operation with the German manufacturer AEG Telefunken. It is a small portable cryptographic machine that was crypto-compatible with NATO CEROFF equipment, such as RACE (KL-51) and Aroflex. Picoflex is also known as UA-8035 and as the ANT Telekrypt-Mini [1]. A cut-down version of it, called Miniflex, was produced for civil applications. In all, over 300 units were made.

Picoflex is a compact light-weight field-grade off-line encryption/decryption device for written messages. The encrypted text is formatted into 5-letter groups containing only the 26 letters of the Latin alphabet and no punctuation marks.

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, morse code or telegraphy over normal PSTN telephone lines or via radio connections.
Typical Philips Picoflex unit with thermal printer and acoustic modem

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.

The keyboard was originally covered by a transparent silicone cover, protecting it against dust and humidity, but as this silicone foil becomes opaque and brittle over the years, it was subsequently removed from most units. It has also been removed from the unit shown here.

Picoflex in carrying case
Picoflex in carrying case (top view)
Pico flex with acoustic coupler
Picoflex with printer and modem
Picoflex main unit
External PSU with battery-replacement adapter
Using the acoustic coupler
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.

NATO olive-green aluminium transport case
Picoflex encryptor
Thermal printer in TEMPEST-proof enclosure
Military-grade radio and telephone modem
Acoustic coupler for analogue telephone
External power supply unit (PSU)
Military-grade microphone/speaker combination
Carrying case
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).
Picoflex in carrying case

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.

Picoflex in carrying case
Picoflex in carrying case (top view)
Main unit
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 transparent foil protecting the keyboard, but these foils became brittle and white over time.

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.
Picoflex main unit

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 printer (when 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, Telefunken 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.
Using the printer

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.

Picoflex printer
Picoflex printer
Picoflex printer
Printer with opened TEMPEST door
Using the printer
Philips stock photographs showing a Picoflex with the earlier printer
Miniflex with the original printer design

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.
Picoflex modem

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.

Picoflex modem
Left side of the Picoflex modem, showing the sub-D socket for connection to the main unit.
Modem bolted onto the Picoflex
Picoflex with acoustic coupler
Using the acoustic coupler
Handset connected to the modem
Using a military handset
Military audio connector

Acoustic Coupler
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.
Acoustic coupler

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 stock photograph from Philips Usfa [4] with an acoustic coupler that is connected directly to the right side of the Picoflex, instead of the modem.

Acoustic coupler
Using the acoustic coupler
Using the acoustic coupler
Using the acoustic coupler
Military audio connector
Military audio connector

External power supply
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 (TEMPEST). The filter is present in order to prevent unwanted information leakage via the mains. Inside the green filter block is a Siemens mains filter.
External PSU with battery-replacement adapter

External PSU with battery-replacement adapter
Mains adapter and filter
Filter interior
Battery pack-shaped plug
Removing the batteries
Removing the batteries
Fitting the mains adapter
Picoflex with mains adapter

Development of the Picoflex started in 1976. It was intended as miniature cryptographic device for portable and field applications. It was also aimed at possible NATO evaluations such as MERCS (also known as MERSEX) and CALL SIGN. AEG-Telefunken 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 [5] of the first prototype of PICOFLEX, that was also present in the (never published) sales brochure of 1976 [6].

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 [2]. The MERCS evaluation was later won by the Norwegian PACE crypto device, built by Lehmkuhl (Kongsberg).
Artist impression of the PICOFLEX prototype in mid-1976

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 [2].

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 ANT (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 [1].

Cryptographic algorithm
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 Aroflex 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.

Picoflex processor board
Power section and tamper switch
Close-up of processor board
Close-up of processor board
Memory board with CONFI ROMs, EPROMs and Crypto Module.
Close-up of Crypto Module
This was probably developed and built by Telefunken. TEMPEST-proof.
Close-up of the filters
The Picoflex is known under the following names and designators:

  • Picoflex
  • Telekrypt-Mini
  • UA-8035
Description Philips ID (12NC) Comment
Processor board 4322 082 08600 -
Crypto board 4322 082 09850 with confidential crypto module
  1. Jane's Military Communication 1986
    ISBN: 0-7106-0824-1

  2. Philips Internal Memo L/5636/AvdP/JG
    23 August 1982, page 5.

  3. Philips Usfa BV, Introducing Philips Usfa BV
    26-page full-colour brochure of Philips Usfa BV and its products. 1983.

  4. Philips Usfa/Crypto, Picoflex stock photograph
    Crypto Museum Collection.

  5. Philips Usfa BV, Short Description of the Off-Line Equipment Picoflex
    Written in cooperation with AEG-Telefunken, Frankfurt am Main (Germany).
    Description 13927-E-876, August 1976.

  6. Philips Usfa BV, Picoflex, Miniaturized Off-Line Encryption Device
    Preliminary sales brochure of the initial PICOFLEX device (never published).
    Datasheet 13814-E-676, June 1976.
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Crypto Museum. Created: Tuesday 06 March 2012. Last changed: Tuesday, 11 February 2020 - 07:28 CET.
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