iPhone users concerned about government surveillance efforts putting unencrypted calls at risk now have a free app at their disposal that brings secure communication to the Apple phone.
Open WhisperSystems, developers of RedPhone for Android, have developed a similar app for iPhone called Signal, which was released today.
Signal, said developer Moxie Marlinspike, provides free, worldwide encrypted voice calls for iPhone and is compatible with RedPhone. Marlinspike said in today’s announcement that later this summer, Signal for iPhone will be expanded and will support secure text communication compatible with the project’s TextSecure for Android app.
“Signal will be a unified private voice and text communication platform for iPhone, Android and the browser,” he said, adding that TextSecure and RedPhone will be combined into a single Signal app for Android, and that a browser extension is being developed.
The core encryption technology in Signal is the ZRTP protocol created by PGP encryption inventor Phil Zimmermann. ZRTP negotiates encryption keys between endpoints in a VoIP call. Signal won’t be the first secure phone app built on the protocol; Zimmermann’s own Zfone project and Silent Circle apps stand atop ZRTP.
For now, users can make calls only to other users who have the app installed. The app then presents the user with two words on the call screen that the caller must read them aloud in order to authenticate the call.
Starting with the release of SSLstrip, which exposed vulnerabilities in SSL encryption by automating man-in-the-middle attacks that prevent browsers from establishing SSL connections, to the development of Convergence, a system of notary servers meant as an alternative to certificate authorities, Marlinspike has been a longtime crusader for privacy and secure communication.
“We want everyone to have access to advanced secure communication tools that are as easy and reliable to use as making a normal phone call or sending a normal text message,” Marlinspike said.