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Secure Telephone Unit, generation 3
The STU-III is the last of a series of analog
secure telephone units,
developed by the National Security Agency
(NSA) in the United States.
STU is the abbreviation of Secure Terminal Unit.
The STU-III was introduced in 1987 as the successor
to the STU-II.
The units were built by various manufacturers, such as
Motorola,
RCA and AT&T.
There are different versions, for desktop use and wall mounting,
with a built-in modem for fax and data transmission.
It was succeeded in the 1990s by the STE
and eventually by the SCIP standard in the 2000s.
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The image on the right shows a typical STU-III unit. The one shown here is the
top-of-range SECTEL 2500 from Motorola.
It has a black case, made of metal and plastic, but it was also available
in beige. It is capable of sending voice and data at 2400, 4800 and 9600 baud.
A similar Motorola SECTEL
was used in 2001 by former US president George W. Bush to liase with
his security advisors just after the 9-11 attacks on the World Trade Center
in New York, whilst visiting Emma E. Booker Elementary School
in Sarasota (Florida, USA) (see below).
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Several hundreds of thousands STU-III phones were produced. They were used
in the US and some allied countries. Although the phones
have now been discontinued and are gradually being phased out,
many remain in service today. STU-III uses
NSA Type 1
or Type 2 encryption,
allowing conversations at all levels of security classification,
up to Top Secret.
Special lower grade variants, with
Type 3
and Type 4 encryption,
were produced for other customers.
STU-III phones covered on this website:
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A special version of the STU-III, called the STU-II/B
was developed for use by NATO forces. It was similar in appearance to the
STU-III, but had more keys on the keypad to allow backwards compatibility
with AUTOVON and IVSN networks. It also had a standard military key-fill
connector at the rear.
It replaced the NATO variant of STU-II.
More about STU-II/B...
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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). Then, one of the parties initiates
the secure conversation by pressing the Secure button.
After a 15 seconds delay, during which 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.
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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).
When travelling, the Secret Service always has a STU-III unit readily
available in a nearby room.
Moments after the attack, Bush used a Motorola SECTEL to speak with
his security staff.
STU-III phones allow secure conversions over standard (insecure) analog
telephone lines, up to the level of Top Secret.
More...
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The STU-III standard was developed in 1987 by the NSA and
several manufacturers were allowed to produce secure telephones based
on this standard, such as:
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© Copyright 2009-2011, Paul Reuvers & Marc Simons. Last changed: Tue,27 Dec 2011.17:47:31
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