The company that revolutionized Internet search is now unveiling a sort of online underground tunnel — a way for people in restrictive countries like Iran and Syria to get around digital censorship and surveillance.

The idea behind the tool — essentially a button for browsers — called uProxy, is simple: People in countries such as the United States provide their trusted friends a secure connection so that they can see and use the unrestricted Internet. …

“These are going to be useful additions to the activist toolkit,” said Philip Howard, a professor at the University of Washington who has written about the impact of social media on political change.

“Authoritarian governments have started figuring out how to use social media to spy on activists and control political conversation,” he said. “Any new tool that lets people network with family and friends in a secure way is likely to have a political impact.”