In a coup for privacy advocates, strong end-to-end encryption is coming to Whatsapp, a cross-platform instant messaging app with more than 500 million installations on the Android platform alone.
Until now, most popular messaging apps for smartphones have offered woefully inadequate protections against eavesdropping. Whatsapp, which Facebook recently acquired for $19 billion, has itself been criticized for a series of crypto blunders only spooks in the National Security Agency would love. Most other mobile apps haven't done much better, as a recent scorecard of 39 apps compiled by the Electronic Frontier Foundation attests. Many fail to implement perfect forward secrecy, which uses a different key for each message or session to ensure that an adversary who intercepts a key can't use it to decrypt old messages. The notable exception among popular messaging apps is Apple's iMessage, but it's not available for Android handsets.
Enter Moxie Marlinspike, the highly regarded security researcher and principal developer of TextSecure, an SMS app for Android. Over the past three years, his team at Open Whisper Systems has developed a open encryption protocol for asynchronous messaging systems. That specification is now being incorporated into Whatsapp.The term asynchronous means that the endpoints don't need to wait for a message from a server or other party to function properly. That's what allows one person to send a burst of a dozen messages while the other remains idle. Implementing strong end-to-end crypto on such systems is especially challenging, particularly when it comes to devising a way to implement forward secrecy. But as Ars reported last year, TextSecure devised a clever technique for doing just that.
For now, Whatsapp encryption is limited to the Android platform, and even then it doesn't work for group messages or for messages containing photos or videos. In a blog post, Open Whisper Systems said those limitations will be addressed in future updates. Developers are also working on options for key verification, so users can make sure a key truly belongs to the person they want to communicate with, rather than an adversary digitally impersonating that person.
Until now, user-friendly strong crypto has been something of an oxymoron. If Whatsapp makes good on its promise to bring strong crypto to iOS and other platforms, it could change that. In the process, it very well may make NSA-style surveillance much harder if not impossible to carry out on a billion or so users.
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