At Open Whisper Systems, 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.

Over the past year, we’ve been working to bring the privacy software we’ve developed for Android to the iPhone, and today we’re releasing Signal – free, worldwide, encrypted voice calls for iPhone, and fully compatible with RedPhone for Android.

High Privacy, Low Friction

Signal uses your existing number, doesn’t require a password, and leverages privacy-preserving contact discovery to immediately display which of your contacts are reachable with Signal. Under the hood, it uses ZRTP, a well-tested protocol for secure voice communication.

Signal was designed specifically for mobile devices, using a jitter buffer tuned to the characteristics of mobile networks, and using push notifications to preserve battery life while still remaining responsive. Signal is also Free and Open Source Software, allowing anyone to audit the code for correctness or help contribute improvements. The project even pays out a percentage of donated Bitcoin for every merged pull request.

Secure Calls Are Just The Beginning

Signal will be a unified private voice and text communication platform for iPhone, Android, and the browser. Later this summer, Signal for iPhone will be expanded to support text communication compatible with TextSecure for Android. Shortly after, both TextSecure and RedPhone for Android will be combined into a unified Signal app on Android as well. Simultaneously, browser extension development is already under way.

The Team

Signal for iPhone is the result of hard work and heavy lifting from our friends at Twisted Oak Studios, design from Tyler Reinhard, and some last-minute heroics from Frederic Jacobs and Christine Corbett.

Signal is free. Give it a try!