The Arab Spring showed that the power of the Internet and Web communications is a multi-edged blade, with activists able to organize through social media and to get their stories out, and authoritarian governments often able to target the activists by following the trail of digital crumbs.

Among the conspicuous sources of information are the chat transcripts often kept on commercial servers, making it easy to see who was talking, what they talked about, and when the conversations took place. Cryptocat and a few other services disguise the content of chat messages so that they look like gibberish to anyone who does not have the encryption key. There is nothing new about encryption technology, but it is a brain-breaking subject, and the tools for using it are tricky.

Mr. Kobeissi started building Cryptocat a year ago in his bedroom with the goal of making it simple to encrypt an online conversation. He had help last weekend from the Guardian Project, a group of developers who are trying to make mobile phones secure. They figured out a way to encrypt a chat on an Android phone by shaking it, taking advantage of the motion detectors in many smartphones. This will generate the digits that are part of the encryption process.

“You can dance with your phone to encrypt it,” Mr. Kobeissi said.

Up to 10 people can speak privately to one another at a time in a Cryptocat chat room, a feature that distinguishes it from other encryption chat services. It is not ready for use by people in life-and-death situations, Mr. Kobeissi said, but it can give people a place to avoid everyday monitoring of routine conversation.

“Cryptocat is an enabling, positive technology, and it’s an alternative,” said Jacob Appelbaum, a developer with the Tor project, which routes Web traffic in ways that help disguise sites that people have visited. “A key thing here is that it is an experiment, with valid criticisms. It’s not perfect. But it is important that we have people who are interested and knowledgeable about computer security who are working on these things, not just for money, and not just to break into people’s computers.”