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Zfone libZRTP Software Development Kit (SDK) Documentation

Zfone is our new secure VoIP phone encryption software. VoIP developers may license the Zfone Software Development Kit to add Zfone's ZRTP protocol to their VoIP applications. This SDK is suitable for inclusion in software VoIP clients, firmware for hardware VoIP phones, VoIP PBX servers, mobile VoIP clients, and SIP border control servers. The SDK enables your VoIP application to interoperate and make secure calls with the rest of the ZRTP community.

For general information about the ZRTP SDK, including licensing information, see the Zfone libZRTP SDK page.

Zfone SDK Documentation for Developers

This is the Zfone SDK documentation page, providing for developers an extensive reference manual for how to use the SDK's API in a VoIP application. You may find the color illustrations especially useful, particularly in the libZRTP Developers Guide.

Apart from How to Get Up and Running Quickly with libZRTP, the libZRTP Developer's Guide and the Guide to the libZRTP Test Suite, the rest of the API documentation is derived directly from the source code and its embedded comments, by using the Doxygen utility.

We're still posting frequent improvements to the SDK documentation on this web page, so keep coming back here for the most up-to-date version.

One note about the writing style: Much of this software and documentation was developed in Ukraine by engineers whose native language is Russian and Ukrainian.

libZRTP SDK Documentation

Follow this link to the online web-based libZRTP SDK documentation.

Evaluate the libZRTP SDK

Register to Download Zfone SDK

To evaluate the libZRTP SDK, go to our Zfone Register-to-Download Page and select the Linux version, which includes full source code, including the libZRTP SDK. Even if you plan to use it for a non-Linux platform, you should download the SDK in the Linux version, because it is the same SDK on all platforms, and it has a make file to build it for multiple platforms, including Windows. The Linux release of the Zfone application provides a good example of how the libZRTP SDK can be used in a real application.

ZRTP Internet Draft

The SDK documentation frequently refers to things that are defined in the ZRTP Internet Draft. Follow this link to the ZRTP Internet Draft to view the current state of the draft in HTML, PDF, and text format.

Wireshark ZRTP packet dissector

If you are developing VoIP applications that use the ZRTP protocol, you may want to use the popular open source Wireshark protocol analyzer (formerly known as Ethereal) to inspect ZRTP packets. To make Wireshark recognize and dissect ZRTP packets, check out our nifty ZRTP packet dissector patch for Wireshark.


"Zfone", "libZRTP", and "whisper in someone's ear from a thousand miles away" are all trademarks of Philip Zimmermann.

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