Just like the US highway infrastructure, Tor needs new bridges. The encrypted anonymizing “darknet” that allows activists, journalists, and others to access the Internet without fear of censorship or monitoring—and which has also become a favored technology of underground groups like child pornographers—is having increasing difficulty serving its users in countries that have blocked access to Tor’s entry points. Tor bridges are computers that act as hidden gateways to Tor’s darknet of relays. After campaigning successfully last year to get more volunteers to run obfuscated Tor bridges to support users in Iran trying to evade state monitoring, the network has lost most of those bridges, according to a message to the Tor relays mailing list by Tor volunteer George Kadiankakis.

“Most of those bridges are down, and fresh ones are needed more than ever,” Kadiankakis wrote in an e-mail, “since obfuscated bridges are the only way for people to access Tor in some areas of the world (like China, Iran, and Syria).” Obfuscated bridges allow users to connect to the Tor network without using one of the network’s known public bridges or relays as an initial entry point.

Obfuscated bridges have become a necessity for Tor users in countries with networks guarded by various forms of deep packet inspection technology, where censors have put in place filters that spot traffic matching the signature of a Tor-protected connection. Some of these censors use a blocking list for traffic to known Tor bridges. To circumvent detection, Tor users can use a plugin called a “pluggable transport” to connect to an obfuscated bridge and mask their network signature.