Meredith Whittaker, president of encrypted chat service Signal, doubled down on her criticism of proposed British online safety legislation, calling the government’s plan to require a special back door to access encrypted messages “mathematically impossible” and vowing to exit the U.K. market if it becomes law.

“They would order us to implement it. We would not,” Whittaker said at the Fortune Brainstorm Tech conference in Deer Valley, Utah, this week.

In an onstage conversation with Roy Bahat, head of Bloomberg Beta, Whittaker said one of her primary missions is to prevent the dangerous trend of socially accepted surveillance.

“I think what has happened over the, you know, handful of decades in which the surveillance business model has interpolated our core infrastructure—to the point that we’re surveilled in to an extent we don’t have a sense of—is that that choice has been made for us,” Whittaker said.

Signal’s unwavering mission, echoed by Whittaker herself, is to prioritize user privacy and security above all else. The nonprofit’s end-to-end encryption protocol ensures that messages remain strictly confidential, accessible only to trusted recipients. Journalists, government officials, and tech entrepreneurs like Elon Musk and Marc Andreessen rely on Signal for secure communication. However, Signal, like its counterparts Telegram and WhatsApp, are not immune to bad actors who desire privacy for illicit activities, like drug dealers, weapons traffickers, or hackers distributing malware.

Thus, the U.K. believes a back door is necessary to prevent such illicit activities from occurring. The country’s online safety bill, first drafted in May 2021, aims to give the government the authority to demand backdoor access to all end-to-end encryption systems. While the government claims it enhances online safety by ensuring social media platforms remove illegal content like revenge porn and hate speech, the bill is fiercely criticized by tech giants, security experts, and privacy advocates—potentially leading to an encryption exodus in the U.K., TechCrunch wrote.

“You cannot create a back door that only the good guys can go through,” Whittaker said, adding that it’s “mathematically impossible” and would “undermine the security of our core communications, core infrastructures.”

Whittaker, who joined Signal in 2022, has been an advisor on A.I. for the U.S. Federal Trade Commission. She also was one of the leaders of the 2018 walkouts at Google, in protest of the company’s privacy practices and its response to internal cases of sexual misconduct. She resigned from Google in 2019.

In her discussion with Bahat at Brainstorm Tech on Tuesday, Whittaker cited a multitude of examples of the perilous situation that is created when allowing a government access to user’s private messages. One instance that Whittaker expounds on is a mother in Nebraska, who faces up to two years in prison along with her 18-year-old daughter, for giving abortion pills to her daughter. Detectives served Facebook (whose parent company also owns WhatsApp) with a search warrant for access to their DMs, which aided in the prosecution, Vice reported.

“What is right is we don’t let one massive corporation with very little oversight determine the surveillance society we live in, [in] collaboration with governments,” Whittaker said.

Despite Signal’s modest user base of 125 million downloads, significantly dwarfed by WhatsApp’s 2 billion users, both companies have made a resolute commitment: They will exit the U.K. if the Online Safety Bill is enacted. Whittaker said onstage that “the anti-encryption, sort of regulatory agenda,” which “snuck in around 2018” has alarmed her.

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