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Racal MA-4471
Secure phone adapter

The MA-4471 is secure telephone adapter developed around 1996 by Racal COMSEC Ltd in the UK. It is an external device that converts a standard telephone set into a secure voice terminal, allowing secure speech over an insecure telephone network. The MA-4471 is not well-known and the design is based on the military MA-4470 voice encryption unit.
 
The image on the right shows the MA-4471 with its sloped control panel at the front. The top surface of the unit is large enough to place a standard telephone set on. All controls are accessible from the front.

At the rear, the MA-4471 has only three connections: one for the power supply unit, one for the phone and one for connection to the telephone line. The unit is clearly designed exclusively for the UK market, as it features the proprietary British phone connectors, rather than the more common modular jacks.
  
Racal MA-4471 Secure Phone Adapter

The MA-4471 communicates with the user via a small LCD display at the front. To the left of the display are two coloured buttons to select between CLEAR and SECURE speech. To the right of the display is a small numerical keypad with the digits 0-9. Additional keys are hidden behind a small panel at the right. These keys are used when entering the cryptographic key(s). Also behind the panel is a 5-pin Fisher socket for the connection of a key fill device, as an alternative to entering keys manually.

At present, we have no further information about this device. If you know more, or if you happen to have a manual for this unit, please contact us. It is unclear whether the MA-4471 has been distributed widely and whether they are still in use today. As the MA-4471 was introduced just before Racal was taken over by Thomson (now Thales) it is quite possible that this has prevented a wide-spread roll-out.
 
Racal MA-4471 Secure Phone Adapter Racal MA-4471 Secure Phone Adapter Display and controls Hidden controls The keypad Control pane; Rear panel Rear panel

 
Interior
After opening the unit, it becomes clear that the MA-4471 is not TEMPEST compliant. The two PCBs, a digital board and an analog board, are placed inside a plastic unshielded case. Furthermore, the entire encryption is carried out in firmware and there are no anti-tamper provisions, suggesting that this device was only intended for medium-grade encryption.
 
The image on the right shows the 8-bit Toshiba AMPZ84C00 processor that is running here at 6 MHz. Aside the processor are two 8 KB static RAM chips (TC5564) and an EEPROM. Encryption takes place completely in the digital domain.

The CPU (the digital board) is nearly identical to that of the military MA-4470. The same 8-bit processor and peripheral ICs are used and the controls are also very similar. The main difference is in the analog circuitry. The audio in/out circuitry and the telephone line interface are both on the so-called analog board.
  
CPU and memory

The MA-4471 was clearly designed for the UK market, as it is wired for the UK telehone network. There is no reason why it shouldn't work in another country though, provided that proper conversion cables or plugs are used.
 
Interior Digital Board Analog Board CPU and memory Controller and firmware Phone line interface Alanog Board detail Audio circuitry

 
Further information

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Crypto Museum. Last changed: Sunday, 31 October 2010 - 10:57 CET.
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