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← Philips Crypto FILL
Handheld radio with digital encryption
PFX-PM was a handheld half-duplex VHF/UHF FM radio with strong built-in
voice encryption,
introduced in 1990 by Philips Usfa in Eindhoven (Netherlands).
The radio is based on the PFX handheld radio made by Philips Radio
Communication Systems (RCS, formerly: Pye) in Cambridge (UK),
and is enhanced with a high-end half-duplex encryption module
developed by Philips Usfa.
The encryption module is also known as UP-2093/xx, with the xx-suffix
indicating the version.
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In order to accomodate the encryption module, the body of the radio is
somewhat longer than that of the standard version. The radio was available
in two versions: one for the 2-meter band (150 MHz) and one for the 70-cm
band (400 MHz), plus the necessary sub-bands.
The image on the right shows a typical PFX-PM that was made for the 2-meter
band. Since it is identified as LVA, it is a low-power variant (L)
with 2k kHz channel spacing (V) and a frequency range of
148-162 MHz or 160-174 MHz (A). It is shown here with the
TP1962 instruction booklet.
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Detailed information about the PFX radio is available on Jan Buiting's
excellent website about his Philips Mobile and Portable radio Collection [5].
Note that the frequency range is either 148-162 MHz (A1) or
160-174 MHz (A2) but not both. One can only tell the difference by opening
the unit.
Also note that the PFX-PM always has a channel spacing of 25 kHz rather than
the more common 12.5 MHz. The reason for this is that digital Continuous
Variable Slope Delta modulation (CVSD) is used, which requires a bandwidth
of at least 16 kHz in order to obtain a good voice quality.
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Secure speech is provided by the encryption module, which consists of
three stacked PCBs plus a sealed Crypto Module developed
by Philips Usfa. By placing components at both sides of each
PCB, the encryption unit could be fitted inside the CTCSS 1
compartment of an extended PFX.
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The image on the right shows the three stacked circuit boards
that form the encryption unit, with the sealed UP-2093 Crypto Module
inserted into a socket at the top. At the front corner, the 3V miniature
lithium battery is visible. It is used to retain the cryptographic keys
in CMOS memory.
The three boards below the Crypto Module hold the DA converter, the
CVSD delta modulator, the DA converter, the audio interfaces and some
additional 'glue logic'. The actual encryption and decryption takes place
inside the UP-2093 unit.
Timing is provided by a regular 6.4 MHz crystal.
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The upper part of the crypto module cannot be opened as it is sealed in some
kind of very tough foam than can't be removed without damaging the components.
The rather unique photographs below show an engineering prototype of the
module, revealing what is normally hidden by foam.
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The crypto-module is in fact a PCB with four chips at the
top surface.
At the top right is the custom-made
OQ4434 crypto-chip
(ASIC) with its typical
golden top cover. The image on the right also shows a couple of bare OA4434
chips, one of which is shown without its golden cover.
At the top left is a one-time programmable Intel 87C51 microcontroller that contains the control firmware.
At the front are two Programmable Array Logic ICs (PALs).
The other side of the PCB (bottom)
contains the buffers and the glue logic that interface the unit
to the rest of the radio.
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CTCSS = Continuous Tone Coded Squelch System.
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With every crypto system, the creation and distribution of cryptographic keys
requires special attention and security measures. The PFX-PM is no exception
to this rule. Philips RCS created a special portable programming kit for the
creation and distribution of up to four different keys.
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The programming kit consisted of a software package that converts a standard PC (DOS)
into a Master Key Programmer (MPK). The software allows the person responsible for
management of the keys, to create four keys automatically — using a random number
generator (RNG) — or to enter them manually
in hexadecimal format.
Once the keys are generated, the external Slave Key Programmer (SKP) — shown in the
image on the right — was used to transfer the keys to the various PFX-PM radios.
The SKP is connected to the PFX-PM radio by means of a special fill cable.
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The SKP (right) is housed in the case of a PFX radio.
Please note that both the radio and the SKP should be powered by their own
batteries (not shown here).
The special transfer cable has identical connectors at both ends,
allowing it to connect to the accessory socket at the side.
The SKP could also be used to transfer the keys to further SKPs.
It has two buttons: one on top of the unit (test) and one on the side for
starting the transfer (the former PTT button). The speaker of
the SKP is used for communication with the user. A single beep indicates an error,
whilst a double beep is sounded after a key has successfully been transfered.
A low-battery condition is indicated by three short clicks on the speaker of
the SKP.
Changing the battery should take less then one minute in order not to lose
the key material stored in the SKP's memory.
The SKP cannot be turned off and will always
consume a little bit of power in order to retain the crypto keys.
Please note that although the PFX-PM has room for 8 crypto keys,
the SKP software only allows 4 of them to be altered.
This is because a longer 5th key is permanently set by the software
(hard-coded), allowing secure communication even when the keys are lost
or have become invalid.
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- Philips RCS, PFX-PM Portable Radio with Digital Encryption, Operating Instructions
TP1962, 1 November 1989
- Philips RCS, Master Key Generator and Programmer (MKP) for PFX-PM, User Manual
TP875, 1990
- Philips RCS, Slave Key Programmer (SKP), User Guide
TP1992 issue 1, 1990
- Philips RCS, Philips digital secure speech system
Brochure with all Philips crypto radio products.
- Jan Buiting, PFX Series
Website Philips Mobile Radio Collection.
Re-retrieved February 2018.
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© Crypto Museum. Created: Saturday 10 March 2012. Last changed: Saturday, 24 February 2018 - 15:40 CET.
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