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
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.
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 .
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
The development of the STU-III/SECTEL range was the responsibility of
Motorola's Government Electronics Group (GEG) in Scottsdale
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) .
Below are some examples of the use of the SECTEL 1500 (STU-III)
by at least four successive US Presidents.
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 
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 
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 .
Neither do we known what the white device at the bottom is.
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.
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 . 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 .
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
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:
- 0V (GND)
- 0V (GND)
- 0V (GND)
- Wikipedia, LPC-10 Vocoder
FS-1015 standard. Retrieved July 2011.
- National Security Agency, Cryptologic Excellence: Yesterday, Today and Tomorrow
Brochure at the event of the 50th anniversary of the agency 1952-2002. p. 16.
- Eric Draper, Photographs of President George W. Bush during the 9/11 attacks
AP Photo/The White House. 11 September 2001. Retrieved, June 2011.
- National Security Agency, Photograph of George W. H. Bush using a STU-III phone
NSA Website. Retrieved February 2013.
- Annual Report 1985, Government Electronics Group
Motorola Inc., 23 January 1986. Page 12.
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?|
© Crypto Museum. Created: Sunday 11 July 2010. Last changed: Tuesday, 17 January 2023 - 13:10 CET.