media: WiFi, UMTS, EDGE, GPRS, Satellite IP modem, GSM CSD, ISDN Implementations ZRTP has been implemented as GNU ZRTP which is used in Twinkle GNU ZRTP4J which is used in Jitsi (formerly SIP Communicator). ortp for use in Linphone. libzrtp which can be used in FreeSWITCH. Signal and its predecessor, RedPhone, used ZRTP for encrypted calls on Android and iOS. As of March 2017, Signal's voice and video calling functionality uses the app's Signal Protocol channel for authentication instead of ZRTP. CSipSimple is a free application for Android OS which fully supports ZRTP PhonerLite softphone for Windows supports ZRTP Commercial implementations of ZRTP are available in RokaCom from RokaCom, and PrivateWave Professional from PrivateWave and more recently in Silent Phone from Silent Circle, a company founded by Zimmermann. There is also Softphone from Acrobits. Draytek support ZRTP in some of their VoIP hardware and software. A list of free SIP Providers with ZRTP support has been published. References External links RFC 6189 — ZRTP: Media Path Key Agreement for Unicast Secure RTP Cryptographic protocols