A Secure Terminal Equipment desk set. Note slot in front for Fortezza PC Card.

How secure telephones work

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 However, this system has now been replaced by the Secure Terminal Equipment (STE) and SCIP standards which defines specifications for the design of equipment to secure both data and voice.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 by Philip Zimmermann's based on the well recognized VoIP encryption standard ZRTP based on an open standard.

Privacy issues

The concerns about massive growth of telephone tapping incidents lead to growing demand for secure telephones. Several companies offer their products, eg. Swiss PrivateGSM, Dutch CryptoPhone, Germany Secure Phone by securITus, Slovak Silentel SecureCall, SecureGSM, American Ripcord Networks, or the secure telephone division of Siemens AG.

VOIP vs direct connection phones

As the popularity of VoIP grows, secure telephony is becoming more of commonplace and less the lonely domain of spies and civil libertarians.

Many major hardware and software providers offer it as a standard feature. What used to only be available at high expense and to a limited number of people is now freely available.

Other examples include the Gizmo Project 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 It's also being made available for mobile GSM CSD as a new standard for non-VoIP secure calls.

There are several manufacturers of hardware Analog Telephony Adapters such as Sipura/linksys and Snom which offer easy to use secure options.

Historically significant products

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

Other historical options involved scrambling generally using a form of voice inversion. This was available from electronic hobbyist kit suppliers and is common on FRS radios.

Analog scrambling products exist to this day because some telecommunications circuits, like HF links and telephone lines in the developing world -- are of very low quality.

See also

• Mobile phone tracking
• ZRTP

External links

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