Signal encrypted messaging app appears to be blocked in China

GUANGZHOU, China – The Signal encrypted messaging app has stopped working in China and is now only accessible through a virtual private network (VPN).

China is blocking many foreign apps and services, including those of Facebook and Google. But Signal had previously not been banned by the so-called Great Firewall.

Signal claims to be end-to-end encrypted, which means that the company itself or any third party cannot view the content of messages between a sender and the intended recipient. It also means that the authorities cannot spy on the messages.

CNBC tested Signal on three different devices and the messages did not get through, suggesting it was blocked by authorities. The app was still available for download through Apple’s Chinese App Store.

Signal was not immediately available for comment when contacted by CNBC.

However, the messaging app still worked when used with a VPN. A VPN or virtual private network allows users to protect privacy and bypass internet restrictions by connecting to servers around the world.

Signal blocking in China highlights growing internet censorship in the world’s second-largest economy.

Signal’s downloads spiked earlier in the year after rival WhatsApp changed its terms of service to allow certain data to be shared with parent company Facebook.

The signal is relatively small in China with 510,000 downloads to date from the Apple App Store, according to Sensor Tower. But the app offered a rare way to send encrypted messages through a foreign platform without a VPN.

Yet the dominant messaging app in China remains Tencent-owned WeChat, with over a billion users.