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{{Short description|Secure telephone system}}
{{about|the telephone system||KY 3 (disambiguation)}}
[[File:Ky-3.jpg|thumb|Two stacked KY-3s at the NSA's [[National Cryptologic Museum]]]]
The '''KY-3''' (TSEC/KY-3) is a secure telephone system developed by the U.S. [[National Security Agency]] in the early 1960s. It was one of the first widely accepted voice encryption systems.<ref name="info_sec">{{Google books|OzWoDwAAQBAJ|Information Security Management Handbook, Volume IV | keywords=KY-3}}</ref> The "TSEC" prefix to the model number indicates NSA's Telecommunications Security [[Joint Electronics Type Designation System|nomenclature system]].

It was made by the [[Bendix Corporation]] according to specifications of the NSA. According to information on display in 2002 at the NSA's [[National Cryptologic Museum]], the KY-3 provided high fidelity [[secure voice]] over special wide-band circuits known as "4-wire dedicated drops", since it used [[pulse-code modulation]] encoding for the audio which gave it "high-quality speech". Its overall high power requirements and physical size limited its "tactical" use but gained popularity among executives, diplomats, military leaders and the intelligence community. More than 2,500 units were produced between 1965 and 1967<ref>{{Cite web |title=KY-3 |work=cryptomuseum.com |access-date=13 September 2022 |url= https://www.cryptomuseum.com/crypto/usa/ky3/index.htm }}</ref> and it was one of the first [[telecommunication]] security devices to use transistors packaged into functional modules. The unit was packaged in a grey [[relay rack]] cabinet. The KY-3 was replaced by the [[STU-I]] and [[STU-II]] and remained in use until the late 1980s.<ref name="info_sec"/><ref name="history">{{Cite book| title=A brief history of cryptology| url=https://archive.org/details/briefhistoryofcr0000boon/page/82/mode/2up?q=KY-3 |work=Internet Archive| date=2005 | isbn=978-1-59114-084-9 }}</ref>

==See also==
*[[STU-III]]
*[[Secure Terminal Equipment]]
*[[Secure Communications Interoperability Protocol|SCIP]]

==References==
{{reflist}}

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[[Category:National Security Agency encryption devices]]
[[Category:Secure telephones]]