Secure telephone

A Secure Terminal Equipment desk set.

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 lead 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 talk 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 However, this system has now been replaced by the Secure Terminal Equipment (STE) and SCIP standards which defines specifications for the design of equipment to secure both data and voice.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 created 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 Ripcord Networks product SecurePC with up to NSA Suite B compliant Elliptic Curve math libraries. ZRTP is also being made available for mobile GSM CSD as a new standard for non-VoIP secure calls.

Several manufacturers of hardware analog telephony adapters offer easy-to-use secure options.

The U.S. National Security Agency is developing a secure phone based on Google's Android called Fishbowl.

Historically significant products

SIGSALY exhibit at the National Cryptologic Museum

Scramblers were used to secure voice traffic during World War II, but were often intercepted and decoded due to scrambling's inherent insecurity. The first true secure telephone was SIGSALY, a massive device that weighed over 50 tons. NSA, formed after World War II, developed a series of secure telephones, including the STU I, STU II and STU-III, as well as voice encryption devices for military telephones.

Other products of historical significance are PGPfone and Nautilus (designed as a non-backdoored alternative to Clipper, now officially discontinued, but still available on SourceForge), SpeakFreely, and the security VoIP protocol wrapper Zfone developed by the creator of PGP.

Scrambling, generally using a form of voice inversion, was available from electronic hobbyist kit suppliers and is common on FRS radios. Analog scrambling is still used, as some telecommunications circuits, such as HF links and telephone lines in the developing world, are of very low quality.

See also

• Mobile phone tracking
• SRTP
• SCIP
• TETRA
• A5/1
• ZRTP
• Crypto phone
• Secure voice

External links

• Seminar on crypto phones by Zidu Wang