Signal already offers end-to-end encrypted text and voice messaging. Frequently used by activists and whistle-blowers, Signal presents itself as a trustworthy app that can handle confidential communications. Its audience is diversifying though, leading it to add new features to cater for a broader demographic.
The implementation of video calling completes Signal’s basic messaging capabilities. As with audio calls, video will be fully end-to-end encrypted to prevent interception or re-routing by malicious actors. The feature is currently in open beta and has to be explicitly turned on from within Signal’s settings. You can only start a call if both yourself and your contact have enabled the system.
Signal’s creator, Open Whisper Systems, has completely rewritten the app’s telephony stack to support video calling. Its entire infrastructure has been overhauled, leading to improvements in voice calling performance too. The change completes Signal’s transition to using a modern, dependable calling system, leaving behind legacy code.
When Signal started, much of the technology behind the app was built from scratch, Open Whisper Systems explained. Due to the limitations of early mobile networks, Signal was built around a customised call protocol. The new update marks the final removal of that early mechanism. Signal now runs on WebRTC and a newer in-house protocol for call setup.
Joining the new protocol is support for Apple’s CallKit in iOS 10. This allows third-party apps to show incoming calls directly on the lock screen, like iOS’ stock phone app. Calls can be answered with a single swipe, without unlocking the device.
Although CallKit makes Signal simpler for most users, it does have potential privacy implications for the people most dependent on it. Because CallKit treats every call equally, iOS will log data about Signal calls. They’ll be added to the “Recent Calls” list and uploaded to iCloud if online backup is enabled.
“As well as being able to answer calls directly from your lock screen, you’ll also see Signal calls in the system’s ‘Recent Calls’ list,” explains Open Whisper Systems. “This is because iOS treats CallKit calls like any other call, however that also means some information will be synced to iCloud if enabled. This information includes who you called and how long you talked.”
The risk is low but it’s possible this information could be stolen and used to gain information about a Signal user’s activity. People who want the maximum protection possible should disable Signal’s CallKit integration in Settings. This will stop data leaking out to iOS but also prevent incoming calls directly intercepting the lock screen.
Signal users can try out the app’s new video calling and CallKit features after installing this week’s update available in the App Store and Google Play. Once updated, the settings menu can be used to turn on the additional functionality.
