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Miniflex   UA-8036
Portable cipher unit for civil applications

Miniflex was a high-grade encryption/decryption device for text-based messages, developed between 1976 and 1982 by Philips Usfa in Eindhoven (Netherlands) in co-production with AEG Telefunken in Munich (Germany). The device can be seen as the civil version of the military — NATO-approved — Picoflex. Together, over 300 Miniflex and Picoflex units were produced.

The device was usually supplied in an executive-style briefcase, together with a selection of add-ons, such as a thermal printer, an acoustic modem and a radio interface. The fully self-contained device is powered by 5 internal AA-size penlight batteries, or by an external AC mains adapter.

The image on the right shows the bare Miniflex encryptor, with keyboard, display and internal batteries. It can be used stand-alone for the off-line encryption and decryption of messages, that can subsequently be sent via letter, mail, telex, telegram, morse code, courier or any other means.
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Miniflex is basically a civil spin-off of the military Picoflex (UA-8035). Unlike Picoflex — which uses strong military grade hardware-based encryption — the encryption algorithm of Miniflex is implemented in software and is significantly weaker. The device was intended for use by large corporations, embassies, etc.. The device featured on this page, was used by a major Dutch bank.

  • Civil
    The standard version — featured on this page — is housed in a silver coloured enclosure. In this version , the encryption algorithm is implemented in software, held in an EPROM.

  • Military
    This is basically the civil version, but housed in a military green enclosure, using a variant of the software-based algorithm. This version was offered to non-NATO countries.

  • Picoflex
    This version is housed in a military green enclosure, similar to the one listed above, but uses hardware-based NATO CEROFF encryption, implemented as a sealed module. This version is NATO-approved and is compatible with Aroflex.
Using Miniflex
Miniflex was often seated in an executive style briefcase, that was commonly used by business men in those days, and could therefore be carried inconspiciously. It was intended for civil applications, such as diplomatic services, international banks, oil companies, etc.

The image on the right shows a typical Miniflex configuration built into a thin Samsonite case. The printer is bolted to the left side of the main unit. The acoustical telephone coupler is fitted behind the main unit and connects to it via a plug at the right.

Two black bags with zippers are fitted at either side of the telephone coupler. They contain spare rolls for the printer and a mains adapter that can be used instead of the batteries. The adapter was manufactured by Telefunken.
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Miniflex could hold only one crypto key at a time. Each key was exactly 24 characters long (A-Z and 1-6) and consisted of 20 characters for the key itself, one fill-in character and three for the indicator. The user would take the key from a so-called key list. Once the key was entered, Miniflex would respond with a 5-character code that should match the checksum in the key list. After that, the operator could encrypt or decrypt a message off-line.

Both the cipher text and the plain text could be printed on the (optional) thermal printer that was attached to the left of the main unit. The text is printed in 5-letter groups and two of such groups fit on each line.

This image shows the printer with its lid opened. Inside the printer is the narrow silver paper roll. The transparent lid has an embedded metal grid that gives some degree of TEMPEST shielding. The printer has its own battery pack and power switch.
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Executive style briefcase containing the Miniflex The Miniflex main unit The complete set inside a Samsonite case Close-up of the Miniflex The main Miniflex unit The printer with the lid open The main unit with the printer attached The Telefunken PSU
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Executive style briefcase containing the Miniflex
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The Miniflex main unit
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The complete set inside a Samsonite case
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Close-up of the Miniflex
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The main Miniflex unit
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The printer with the lid open
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The main unit with the printer attached
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The Telefunken PSU

Miniflex was a co-production between Philips Usfa and the German AEG Telefunken. Whilst Telefunken produced the die-cast aluminium case, the power adapter, the keyboard and the display, Philips developed the electronics, i.e. the complete crypto-unit and the central processing unit (CPU).

In order to protect the Miniflex against eavesdroppers, great care was taken to ensure that the unit was TEMPEST proof. This means that the case is well protected against unwanted radiation of power and signals that could otherwise be exploited to recover the original clear text. The level of shielding found in the Miniflex was sufficient for civil applications, but did not meet the military TEMPEST requirements. Especially the thermal printer was notorious for producing sparks, resulting in a high level of unwanted emission.

Military version
The Miniflex shown on this page, is a civil version of the device, hence its silver colour. It was however, also available as a military device, in which case it was painted NATO olive green and featured military connectors. It was intended for military use in non-NATO countries.

The military version of the Miniflex is featured in the 1983 full-colour brochure [1] of Philips Usfa BV. The image on the right is taken from this brochure, and shows a Philips engineer during the development of the military Miniflex.

In the image, the processor board is visible inside an olive-green enclosure. The processor itself has been replaced by a Textronix in-circuit emulator, which was used during the development of the machine. Other photographs in the brochure [1] show the bare machine and an example of its use by military personnel.
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The military variant of the Miniflex was also sold by AEG Telefunken as the Telekrypt-Mini. This military version of the Miniflex (UA-8036) is not to be confused with the far more secure Picoflex (UA-8035). Although they are both housed in the same case, Picoflex is a far more advanced cryptographic device, approved for NATO Secret information, meeting full military TEMPEST requirements. The Philips Usfa brochure is available for download below.

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  1. Philips Usfa BV, Miniflex Operating Intructions
    4-page document describing the use of the Miniflex.
  1. Philips Usfa BV, Introducing Philips Usfa BV
    26-page full-colour brochure of Philips Usfa BV and its products. 1983.
Further information
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Crypto Museum. Created: Tuesday 04 August 2009. Last changed: Tuesday, 06 August 2019 - 15:40 CET.
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