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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 |
Despite the secrecy surrounding the KL-7 and its
history, the mystery is gradually being unravelled as
the NSA releases more and more historical documents and
researchers manage to uncover more and more technical
details of the machine. As a result, a reaslistic computer simulation of the KL-7 is
now available from crypto-historian Dirk Rijmenants in
Belgium.
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