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Secure Telephone Unit · STU-III · Type 1 - wanted item

SECTEL 1500 is a STU-III secure telephone introduced around 1987/88 by Motorola in Seguin (Texas, USA). It was approved for use by the US Government for classification level TOP SECRET and below, and uses secret NSA-developed algorithms for secure communication. It is a STU-III compatible, NSA Type 1 product that can also be used in Type 2 mode for compatibility with the SECTEL 2500. The SECTEL 1500 was also used in Canada and in some other selected countries.

The SECTEL 1500 was designed under the NSA STU-III endorsement program, which implies that it supports at least the LPC-10e (at 2400 baud) and CELP vocoders (4800 baud) in order to be interoperable with the STU-III terminals from other manufacturers, such as the AT&T 1100.

In addition, the SECTEL 1500 offers a far better speech quality by implementing MRELP encoding at 9600 baud, something that the AT&T 1100 doesn't. As a result, the SECTEL range of STU-III terminals became arguably the most popular choice with the various US Government services.

All SECTEL 1500 units contain a secret NSA Type 1 algorithm, plus a Type 2 algorithm that allows interoperability with other STU-III Type 2 devices, such as the Motorola SECTEL 2500. The image above shows a SECTEL 1500 unit that was used by the FBI. The units were taken out of service and were sold on eBay in 2011. Unfortunately though, the cryptographic heart of each unit had been removed before they were sold, as a result of which they are no longer operational.

The exterior of the SECTEL 1500 is identical to the other Motorola SECTEL units. The case is either black or cream, but the controls are always black. The cryptographic functions are enabled by a Crypto Ignition Key (CIK), which is a Datakey KSD-64 Key Storage Device or similar. The SECTEL 1500 was gradually phased out from the mid-2000s onwards and was replaced by the new Secure Telephone Equipment (STE). The last valid STU-III keys expired on 31 December 2009.

The image below provides an overview of the features of the SECTEL 1500. At the rear are the connection to the outside world: the analogue PSTN telephone line, the external power supply unit (PSU) and (optionally) a computer. Also at the rear are backup battery and ZEROIZE button.

All user controls are at the top surface. At the top is a large LCD with 16 function buttons below it, plus another 16 freely programmable speed dial buttons. Towards the front is a regular telephone keypad with the numbers 0-9 plus '*' and '#'. In rest, the handset is placed in the cradle to the left of the keypad. For half-duplex operation, a special handset with an integrated PTT button was seperately available. Handsfree operation is possible, but not in secure mode.

Compatible devices
Motorola SECTEL 2500 (Type 2 and 3 encryption)
AT&T/Lucent 1100 (STU-III) - later sold by General Dynamics
GE/RCA STU-III - later sold by General Electric
Motorola STU-III/R (STU-II and STU-III compatible)
Key Storage Device
Key material is generated externally and loaded into the SECTEL 1500 by means of a so-called Key Storage Device (KSD), such as the KSD-64A manufactured by Datakey Inc. It looks like a plastic toy key and works like starting a car.

The KSD can be used for a variety of purposes. such as: Crypto Ignition Key (CIK), Master CIK, FILL Key (FK), Terminal Activation Key (TAK), Security Activation Key (SAC) and Traffic Encryption Key (TEK).

 More about the KSD-64


At 2400 baud, the SECTEL 1500 uses a 2.4 kbps Linear Predictive Coding algorithm known as Enhanced LPC-10 or LPC-10e. It is based on the FS-1015 or STANAG-4198 standard [1]. The same standard was used in other crypto phones from the same era, such as the Philips PNVX, the Philips Spendex 40, the AT&T 1100 (later: Lucent and General Dynamics), and the American CVAS-III. The LPC-10e algorithm is suitable for half-duplex as well as full-duplex.

At 4800 baud, Code-Exited Linear Predictive Coding (CELP) is used in full-duplex, providing better audio quality. At the highest speed, 9600 baud, an even better algorithm — Modified Residual Exited Linear Predictive Coding (MRELP) — is used in full duplex. The Motorola SECTEL 1500 is the only STU-III phone that could use a Type 1 algorithm at 9600 baud. Speech quality in this mode is better than width the STU-III sets from other manufactuers, such as the AT&T 1100.

The SECTEL 1500 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 virtually any telephone network in the world. The label at the bottom if the unit shown here, indicates that it is approved for use in The Netherlands. If the quality of the (foreign) telephone line is below average, the system gracefully degrades to a lower speed, but maintains its Type 1 cryptographic security.

The development of the STU-III/SECTEL range was the responsibility of Motorola's Government Electronics Group (GEG) in Scottsdale (Arizona, USA). In 1985, GEG received a US$ 15.3 million development award from the National Security Agency (NSA) for a low-cost secure voice/data telephone terminal (LCT) and a secure cellular mobile radio system.

The development became a Motorola team effort led by GEG, with styling and user interface (UI) developed by CS, modems by UDS and a custom large scale integration chip set (custom chips) by GEG itself. These products were released in 1987 as the 3rd generation Secure Telephone Unit (STU-III), and were mass-produced in AIEG's facilities in Seguin (Texas, USA) [5].

Presidential communication
Below are some examples of the use of the SECTEL 1500 (STU-III) by at least four successive US Presidents.

President Ronald Reagan
Ronald Reagan served two successive terms as the 40th President of the United States (1981-1989). During this time he became known as a strong supporter of secure communications. He endorsed, for example, the use of the STU-II secure phone at all levels of the US Government and the Department of Defense (DoD), and made funding available for the development of the STU-III.

President Ronald Reagan using an early (white) Motorola STU-III. © NSA [2]

Towards the end of Reagan's presidency, the STU-III entered service and soon became a beste-seller in government circles. Eventually more than 100,000 units would be ordered. The image above shows President Ronald Reagan using one of the first Motorola Type 1 STU-III phones.

President George H. W. Bush
The next president to use the STU-III, was George H. W. Bush. His administration was in office from 1989 to 1993 and used the STU-III on many occasions throughout his entire presidency. Bush, who served as Vice President under Ronald Reagan (1981-1989) was well aware of the security aspects involved with secure communication.

President George H. W. Bush (Sr) using a black Motorola STU-III. © NSA [4]

The image above shows President George H. W. Bush using a STU-III that is placed on a small table aside his chair. The sign below the table reads: 'SPECIAL TELEPHONE FOR PRESIDENTIAL COMMUNICATIONS'. Although the protograph was taken during his presidency, the exact date and place are currently unknown [4]. Neither do we known what the white device at the bottom is.

President Bill Clinton
William Jefferson (Bill) Clinton served two terms as the 42th President of the United States (1993-2001). Although the STU-III must have been used heavily during the Clinton administration, we have not found any photographic evidence that shows Clinton using such a phone. If you have one, you can help use by sharing it with us.

President George W. Bush
9/11 Attacks at the World Trade Center
On 11 September 2001, the two largest towers of the World Trade Center in New York (USA) were attacked by terrorists. When it happened, president George W. Bush was visiting Emma E. Booker Elementary School in Sarasota (Florida). As the Secret Service had already installed a readily available STU-III unit in a nearby room, President Bush was able to speak with his security staff in Washington only moments after the first impact.

Official White House Photograph by Eric Draper [3]. 11 September 2001.

The image above shows President George W. Bush using his Motorola SECTEL STU-III phone in the foreground, whilst the attack on the second tower is visible on a TV screen at the back. The photo is part of a series of three photographs (see below) that were made by White House photographer Eric Draper at the event [3]. Click for a larger view.

On 9 September 2011, exactly 10 years after the attacks, CNN released an interview with Eric Draper, who was President Bush's personal photographer at the White House at the time. In the interview, several of Eric's photographs, taken on 9/11, are shown alongside CNN footage.

 More about the Motorola SECTEL
 Interview with Eric Draper

AP Photo/The White House, Eric Draper
AP Photo/The White House, Eric Draper
AP Photo/The White House, Eric Draper
1 / 3
AP Photo/The White House, Eric Draper
2 / 3
AP Photo/The White House, Eric Draper
3 / 3
AP Photo/The White House, Eric Draper

Other models
To suit both the safety requirements of the customers and US Government regulations, different SECTEL models were manufactured, all based on the same basic hardware design and enclosure. The firmware and the cryptographic algorithms are different however. The diagram below shows how they are positioned. Only the SECTEL 1000 series and 2000 series are STU-III compatible.


Click any of the balloons above for additional information about the related SECTEL model. The SECTEL 1500 is interoperational with all SECTEL 1000-series and 2000-series devices, including the SECTEL 2500. When communicating with a 1000-series device, it is used in Type 1 mode. When communicating with a 2000-series device, the SECTEL 1500 is used in Type 2 mode.

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:

  1. +12V
  2. -12V
  3. +5V
  4. 0V (GND)
  5. 0V (GND)
  6. +5V
  7. 0V (GND)
  1. SECTEL 1000 & 2000 User's Guide 1
    Motorola Inc., 1987.

  2. SECTEL 1500 User's Manual
    Motorola Inc., 1992.

  3. Quick Reference Guide
    Motorola Inc., 1992. Distributed with [1].
  1. Obtained from the Clinton Presidential Library, on 16 January 2023.

  1. Wikipedia, LPC-10 Vocoder
    FS-1015 standard. Retrieved July 2011.

  2. National Security Agency, Cryptologic Excellence: Yesterday, Today and Tomorrow
    Brochure at the event of the 50th anniversary of the agency 1952-2002. p. 16.

  3. Eric Draper, Photographs of President George W. Bush during the 9/11 attacks
    AP Photo/The White House. 11 September 2001. Retrieved, June 2011.

  4. National Security Agency, Photograph of George W. H. Bush using a STU-III phone
    NSA Website. Retrieved February 2013.

  5. Annual Report 1985, Government Electronics Group
    Motorola Inc., 23 January 1986. Page 12.
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Crypto Museum. Created: Sunday 11 July 2010. Last changed: Tuesday, 17 January 2023 - 13:10 CET.
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