STU-III

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.

There are portable and militarized versions and most STU-IIIs contained an internal modem and RS-232 port for data and fax transmission.

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.

While there have been no reports of STU-III encryption being broken, there have been claims that foreign intelligence services can recognize the lines on which STU-IIIs are installed and that un-encrypted calls on these lines, particularly what was said while waiting for the "go secure" command to complete, have provided valuable information.

Unlike earlier systems, the STU-III's encryption electronics are completely contained in the desk set.

Operational difficulties in using STU-III phones hindered coordination between the Federal Aviation Administration and NORAD during the September 11, 2001 attacks on New York and Washington.

As a result, in addition to having secured voice conversations, users can also use an STE unit for classified data and fax transmissions.

Both STU-III and STE are built on technologies that are proprietary, and details of the cryptographic algorithms (BATON and FIREFLY) are classified.

Although the secrecy of the algorithms does not make the device less secure, it does limit the usage to within the U.S. government and its allies.

Within the Department of Defense, Voice over IP (VoIP) has slowly emerged as an alternative solution to STU-III and STE.

The high bandwidth of IP networks makes VoIP attractive because it results in voice quality superior to STU-III and STE.

Both allies and adversaries of the United States are interested in STU-III, STE, and other secured voice technologies developed by the NSA.