Secure telephone
telephone that provides encrypted call
A secure telephone is a telephone that provides voice security in the form of end-to-end encryption for the telephone call, and in some cases also the mutual authentication of the call parties, protecting them against a man-in-the-middle attack. Concerns about massive growth of telephone tapping incidents led to growing demand for secure telephones.
The practical availability of secure telephones is restricted by several factors; notably politics, export issues, incompatibility between different products (the devices on each side of the call have to use the same protocol), and high (though recently decreasing) price of the devices.
Well-known products
The best-known product on the US government market is the STU-III family. However, this system has now been replaced by the Secure Terminal Equipment (STE) and SCIP standards which defines specifications for the design of equipment to secure both data and voice. The SCIP standard was developed by the NSA and the US DOD to derive more interoperability between secure communication equipment. A new family of standard secure phones has been developed based on Philip Zimmermann's VoIP encryption standard ZRTP.
VoIP and direct connection phones
As the popularity of VoIP grows, secure telephony is becoming more widely used. Many major hardware and software providers offer it as a standard feature at no extra cost.
Examples include the Gizmo5 and Twinkle. Both of the former work with offerings from the founder of PGP, Phil Zimmermann, and his VoIP secure protocol, ZRTP. ZRTP is implemented in, amongst others, Ripcord Networks product SecurePC with up to NSA Suite B compliant Elliptic Curve math libraries.
The public source identifies “Secure telephone” as telephone that provides encrypted call. This brief keeps that definition visible, then builds a research path around Secure, telephone and provides.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Feb 18, 2026. The linked authority identifier is Q10862459.
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This entry incorporates text from “Secure telephone” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.