ZRTP/S

ZRTP/S is an extension to ZRTP protocol. It is designed to make ZRTP-secured calls work across Circuit Switched communication channels such as the traditional telephony networks (GSM, CDMA, PSTN, ISDN, etc) where internet protocol is not available.

On these telecommunication technologies peers can have a sort of “serial connection” through which they send and receive raw digital data.

The communication channel is so narrowband (9.6kbit/s) that it is not possible to run IP (internet protocol over IP) over it.

So, PrivateWave and Philip Zimmermann jointly designed and implemented ZRTP/S. It is a transport and security protocol for Voice over Circuit Switched channel, carefully adapted to be extremely narrowband and minimalistic.

After a year of researching and development, PrivateWave created a library, libzrtps. The library allowed PrivateWave to release the 1^st version of PrivateGSM product - PrivateGSM CSD. It allows users to communicate securely in a point-to-point fashion with the ZRTP end-to-end encryption protocol and with a bandwidth as small as 5400bit/s.

Full specification of ZRTP/S and Source Code will be soon published. Anyone willing to create his own project, improve and eventually establish interoperability between Circuit Switched secure telephony (ZRTP/S over GSM) and Packet Switch secure telephony (ZRTP over IP) can benefit from the publications.

Interoperability represents one of the design goals of the ZRTP/S protocol.