"Over the weekend, we heard reports that Signal was not functioning reliably in Egypt or the United Arab Emirates," Open Whisper Systems writes. "We investigated with the help of Signal users in those areas, and found that several ISPs were blocking communication with the Signal service and our website. It turns out that when some states can't snoop, they censor."
Open Whisper Systems circumvents filtering systems with domain fronting, a technique that routes all messages through a popular domain name -- in this case, Google. All Signal messages sent from an Egypt or UAE country code will look like a normal HTTPS request to the Google homepage.
In order to block Signal in these countries, the governments would have to disable Google.
"The goal for an app like Signal is to make disabling internet access the only way a government can disable Signal," the company says. The blog post continues, "With enough large-scale services acting as domain fronts, disabling Signal starts to look like disabling the internet."