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Motorola SECTEL
Secure telephone unit · STU-III

SECTEL was a series of secure telephones for use on analogue PSTN networks, manufactured by Motorola in Seguin (Texas, USA). Some SECTEL models are STU-III compatible and are based on the 1986/1987 STU-III standard, developed by the US National Security Agency (NSA). Different models were manufactured, with a varying degree of security ranging from Type 1 to Type 4 NSA encryption products [1]. The NSA Type 1 versions were for exclusive use by the US Government.

The image on the right shows a typical black Motorola SECTEL 2500. It is suitable for the transmission of voice and data at 2400, 4800 and 9600 baud, using a variety of compression techniques and encryption/decryption methods.

The phone is very easy to operate. It contains a standard keypad with the numbers 0-9, plus '*' and '#'. A large crisp display at the top is used for interaction with the user. Just below the display are 16 pre-defined function keys. They are used, e.g., to switch between SECURE and CLEAR modes, and to set the audio volume.
Motorola SECTEL 2500 with CIK

Below the function keys are 16 user-definable keys that can be used to store frequency used phone numbers or functions. Memory). They user could write down the names of the memory locations on a small piece of paper, but it is also possible to use a plastic inlay that fits in between the two rows of memory keys (not present in the image above).

Motorola SECTEL phones on this website
Motorola SECTEL 1500 (Type 1 encryption)
Motorola SECTEL 2500 (Type 2 and 3 encryption)
Motorola SECTEL 9600 (Type 4 encryption)
Motorola STU-II/B SECTEL (NATO-version)
15 second delay
A STU-III phone can be connected to any standard analog telephone line (POTS). A call is always initiated in non-secure mode. In order to go secure, both parties have to insert and activate their unique Crypto Ignition Key (CIK). One of the parties then presses the SECURE-button to initiate a secure conversation. After a 15 second delay, during which the baud rate is negotiated, the message keys are exchanged and the phones are synchronised, a secure conversion is possible.

The 10 to 15 second delay is common for all STU-III phones and can be considered a nuisance to the user. Furthermore, valuable information is often given away in the clear voice conversation that takes place before secure mode is entered. This is not the case with the later (fully digital) Secure Telephone Equipment (STE).

Until today, there have been no reports of STU-III units being broken. That does not mean, however, that foreign intelligence services did not gather valuable information from intercepted lines, directly before and after the secure part of the conversation.

SECTEL 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.


Type 1 products use classified (secret) NSA encryption algorithms and are intended only for use by the US government 1 , at the highest level of classification. Type 2 products use unclassified encryption algorithms endorsed by the NSA. They are used for protection of sensitive information between government agencies and approval from the US or Canadian government is required.

Type 3 products use an unclassified, fully public encryption algorithm that is used for protection of sensitive or company-proprietary information. Type 3 is also referred to as NIST Standard DES. It is only sold to US government contractors and approved companies. The SECTEL 3500 is an example of a Type 3 product, whilst the SECTEL 2500 can use both Type 2 and Type 3 encryption.

The SECTEL 9600 is the only phone in this family that uses Type 4 encryption. It is intended for unclassified, non-sensitive information between companies. It uses a non-classified, publicly available and fully published encryption algorithm. It could be sold to all countries except those that were on the US hostile list, but was never a commercial success.

  1. Type 1 products were also used by the Canadian Government.

Motorola SECTEL 1500 (Type 1 encryption)
Motorola SECTEL 2500 (Type 2 and 3 encryption)
Motorola SECTEL 9600 (Type 4 encryption)
Motorola STU-II/B SECTEL (NATO-version)
Presidential communication
For a president, communication with his ministers and advisors is paramount. In the past, the STU-III has proved to be a major 'lifeline' for various presidents whilst travelling through the country or during overseas visits. Generally, a couple of STU-III phones were installed by the US Secret Service, at any likely or unlikely location that the president could possibly visit that day.

As the STU-III had an analogue interface, it could be connected to any POTS telephone wall socket anywhere in the world, allowing a secure conversion over a non-secure telephone line, up to the level of Top Secret. For this reason, the later STE phone still supports analogue connectivity.

The long life-span of the STU-III is illustrated by the fact that it served four US Presidents: Ronald Reagan, George H. W. Bush (Sr), Bill Clinton and George W. Bush (Jr). Although it is quite possible that the suceeding president, Barack Obama, also used the STU-III, there is no photographic evidence of this. Obama is known to have made extensive use of the STE, which was introduced around the time he was installed as the 44th President of the United States.

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.

Ronald Reagan using a STU-III telephone [4]
President Ronald Reagan using an early (white) Motorola STU-III. © NSA [3]

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

Click to see more
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.

AP Photo/The White House, Eric Draper
Official White House Photograph by Eric Draper [1]. 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 [1]. Click for a larger view.

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

 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
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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

  • SECTEL 1500, Type 1, sold for US$ 1800
  • SECTEL 2500, Type 2, sold for US$ 2145
  • SECTEL 3500, Type 3, sold for US$ 3395
  • SECTEL 9600, Type 4, sold for US$ 4495
  1. Robert Crotinger, Motorola STU-III Fact Sheet

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

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

  4. National Security Agency, Photograph of George W. H. Bush using a STU-III phone
    NSA Website. Retrieved February 2013.
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Crypto Museum. Created: Sunday 11 July 2010. Last changed: Saturday, 09 February 2019 - 10:11 CET.
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