China disrupts WhatsApp texts as censor tools grow more powerful

China is tightening the screws on Facebook Inc.’s WhatsApp, honing and employing cutting-edge surveillance technology to disrupt the messaging service as part of a longer-term crackdown on its online spheres.

The latest disruptions are affecting users intermittently across the world’s second-largest economy, intensifying a blocking effort that began around July but has gotten more sophisticated in ensuing months, said Nadim Kobeissi, a cryptographer at Paris-based online security firm Symbolic Software.

This marks another setback for Facebook co-founder Mark Zuckerberg, who’s expressed keen interest in expanding in the country but made little headway. The interference marks a step up from July, when local users began experiencing sporadic issues sending images and voice messages. China is tightening scrutiny over its internet arena in the run-up to the 19th Communist Party congress. It’s slapped fines on companies for failing to screen content, shuttered celebrity gossip sites, and punished chatgroup administrators on Tencent Holdings Ltd.’s WeChat for hosting sensitive content.

Starting last week, WhatsApp users in China began noticing sporadic texting outages as government cybercops played a cat-and-mouse game with the messaging platform, said Kobeissi. The country’s Great Firewall surveillance regime is configured to censor traffic based on connections to servers and addresses. But the Facebook service rotates among multiple server addresses so it takes time for censors to catch up, he said.

“The rotating server addresses keep the network efficient, but it also has an unintended side effect, which is it circumvents censorship of the Chinese Firewall,” said Kobeissi, who focuses on messaging encryption. “It might have taken a while for the Great Firewall to adapt, but it’s catching up.”

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Facebook and WhatsApp didn’t immediately respond to requests for comment outside normal business hours. There was no answer at two published fax numbers for the Cyberspace Administration of China, the nation’s internet regulator.

WhatsApp had until very recently been one of the remaining major messaging services to operate unfettered in China. The company began implementing full end-to-end encryption last year: that means only senders and recipients can see or hear the content sent through WhatsApp, curtailing authorities’ ability to conduct widespread surveillance.

Kobeissi said he suspects censors were able to block WhatsApp images and voice messages based on secure HTTPS protocol, but it took time to upgrade their tools to screen text messages based on “Noise” protocol — a framework that allows WhatsApp to work more efficiently.

The New York Times first reported that censors had stepped in to largely block the service. As of Tuesday however, many users were still able to send messages successfully.