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Motorola SECTEL 9600
Secure Telephone Unit

The SECTEL 9600 was a secure telephone manufactured by Motorola in Seguin (Texas, USA). It uses Motorola's proprietary DVI encryption algorithm, [3] which offers a high level of security. It is classified as an NSA Type 4 product, which means it is for non-sensitive unclassified information, typically intended for business applications. It is not STU-III compatible.

It offers two methods for key management: manual mode, in which keys are generated by the system, and automatic public key (APK) which offers a 'keyless' RSA-based technology for exchanging the keys [2] .

The SECTEL 9600 is capable of sending voice and data simultaneously at different speeds, depending on the quality of the (analog) telephone line. A series of advanced speech processing algorithms have been implemented to ensure superior voice quality at different speeds [1] .
  
Typical view of the Motorola SECTEL 9600 (STU-III)

At 2400 baud, the SECTEL 9600 uses a 2.4 kbps Linear Predictive Coding algorithm known as Enhanced LPC-10. It is based on the FS-1015 or STANAG-4198 standard that is also used with the Philips PNVX crypto phone. It is suitable for both half and full duplex.

At 4800 baud, Code-Exited Linear Predictive Coding or CELP is used in full-duplex, providing better audio quality. At the highest speed, 9600 baud, an even better algorithm, called Modified Residual Exited Linear Predictive Coding or MRELP, is used in full duplex.

The SECTEL 9600 has a built-in V.24/V.32 modem that can also be used for computer data at baud rates ranging from 75 to 9600 baud. It is tested and compliant with most telephone systems around the world. If the quality of the (foreign) telephone line is below average, the system gracefully degrades to a lower speed, but maintains its Type 4 security.

Typical view of the Motorola SECTEL 9600 (STU-III) Close-up of the keyboard showing the SECURE and CLEAR keys at the top left. The ZEROIZE key hidden behind a plastic cap at the rear of the phone. Close-up of the ZEROIZE key Warning on the font panel Power supply unit Standard power cable

Help required
Although all STU-III telephones have now been discontinued and the SECTEL unit itself is not classified, it is very difficult to obtain information about this unit. Any information, such as the user manual, is most welcome. If you can help us in any way, please contact us.

Other models
To suit the various customers and their safety requirements, different SECTEL models were manufactured. They all use the same enclosure and operation is more or less identical. The diagram below shows the positioning of the various SECTEL models.

SECTEL 9600 SECTEL 2500 SECTEL 1500
Connections
The SECTEL 1500 phone is powered by an external Power Supply Unit (PSU) that provides three different voltages: +5V (1.75 A), +12V (250 mA) and -12V (210 mA). The PSU is connected to the 7-pin (or 8-pin) 270° DIN socket at the rear of the unit. The socket has the following pinout:

Power cable pinout when looking into the socket on the SECTEL phone.

Note that the socket may have 8 holes, but that the plug at the end of the PSU cable has only 7 pins as shown in the image above. The standard plug has a so-called twist-lock (also known as a bajonet ring) to keep it secured to the socket, but a standard 7-pin 270° DIN plug will also fit.

Download
References
  1. Motorola SECTEL 9600 brochure
  2. Robert Crotinger, Motorola STU-III Fact Sheet
  3. Motorola SECTEL 9600 features and specifications
Further information
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Crypto Museum. Last changed: Monday, 05 January 2015 - 21:07 CET.
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