STU-III

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STU-III (Secure Telephone Unit - third generation) is a family of secure telephones introduced in 1987 by the NSA for use by the United States government, its contractors, and its allies. STU-III desk units look much like typical office telephones, plug into a standard telephone wall jack and can make calls to any ordinary phone user (with such calls receiving no special protection, however). When a call is placed to another STU-III unit that is properly set up, one caller can ask the other to initiate secure transmission. They then press a button on their telephones and, after a 15-second delay, their call is encrypted to prevent eavesdropping. There are portable and militarized versions and most STU-IIIs contained an internal modem and RS-232 port for data and fax transmission. Vendors were AT&T (later transferred to Lucent Technologies), RCA (now L-3 Communications, East) and Motorola.

STU-III are no longer in service with the U.S. Government, with the last cryptographic keys for the units expiring on December 31, 2009. It has been replaced by the STE (Secure Terminal Equipment) and other equipment using the more modern Secure Communications Interoperability Protocol (SCIP).^[1]