ZRTP
Protocol designed by Phil Zimmermann to secure VoIP.
Used in Z Fone: Zfone is not itself a VoIP client, but lets you make secure calls with your existing VoIP client, by filtering, encrypting and decrypting all your VoIP media packets as they pass in and out of your computer... Zfone has been tested with these VoIP clients: X-Lite, Gizmo (audio, no video yet), X Meeting, GoogleTalk VoIP client (but only when Google Talk is using RTP), Yahoo Messenger's VoIP client (for audio), Magic Jack, and S Jphone. Zfone will encrypt audio and video for Apple IChat calls on MacOs X (Leopard). Zfone has been tested with these VoIP service providers: Free World Dialup, iptel.org, and S I Pphone. It does not work with Skype.
Android apps
See also 2012-04-25-ZimmermannSilentCircle
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