right|thumb|350px|a stu-iii secure telephone (at&t model) stu-iii 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 it has been replaced by the ste (secure terminal equipment) and other equipment using scip, the more modern secure communications interoperability protocol.stu-iii phase out, l3 communications ==versions==  * stu-iii/low cost terminal (lct) designed for use in office environment by all types of users. (motorola sectel 1500, lucent technologies/gd 1100 and 1150) * stu-iii/cellular telephone (ct) is interoperable with all stu-iii versions. works in all continental us mobile network and in most of the foreign cellular networks. * stu-iii/allied (a) specialized version of the stu-iii/lct that is compatible with the stu-ii. it retains all basic stu-iii functions and capabilities and incorporates stu-ii bellfield kdc, stu-ii net, and stu-ii multipoint modes of operation. * stu-iii/remote control interface (r or rcu) * stu-iii/multimedia terminal (mmt) * stu-iii/inter working function (iwf) * stu-iii/secure data device (sdd) * stu-iii/ciphertac 2000 (ctac) ==security==  most stu-iii units were built for use with what nsa calls type 1 encryption. this allows them to protect conversations at all security classification levels up to top secret, with the maximum level permitted on a call being the lower clearance level of the two persons talking. at the height of the commercial comsec endorsement program, type 2, 3, and 4 stu-iiis were man
National_Security_Agency_encryption_devices Secure_telephones