Encryption App ‘Signal’ Fights Censorship With a Clever Workaround

Any subversive software developer knows its app has truly caught on when repressive regimes around the world start to block it. Earlier this week the encryption app Signal, already a favorite within the security and cryptography community, unlocked that achievement. Now, it’s making its countermove in the cat-and-mouse game of online censorship.

On Wednesday, Open Whisper Systems, which created and maintains Signal, announced that it’s added a feature to its Android app that will allow it to sidestep censorship in Egypt and the United Arab Emirates, where it was blocked just days ago. Android users can simply update the app to gain unfettered access to the encryption tool, according to Open Whisper Systems founder Moxie Marlinspike, and an iOS version of the update is coming soon.

Signal’s new anti-censorship feature uses a trick called “domain fronting,” Marlinspike explains. A country like Egypt, with only a few small internet service providers tightly controlled by the government, can block any direct request to a service on its blacklist. But clever services can circumvent that censorship by hiding their traffic inside of encrypted connections to a major internet service, like the content delivery networks (CDNs) that host content closer to users to speed up their online experience—or in Signal’s case, Google’s App Engine platform, designed to host apps on Google’s servers.