Iranian officials have promised more Internet freedom since Hassan Rouhani was elected in June. However, many websites and social networks, like Facebook an Twitter, remain blocked.
The latest victim of Iran's so-called "Filternet" is Cryptocat, a tool that allows for secure and encrypted chat, and is popular with human rights activists and journalists around the world. This appears to be the first time that Iran blocks a secure chat service like Cryptocat.
Cryptocat's website and its server have been inaccessible within Iran since Monday, according to its founder Nadim Kobeissi, independent researchers and the site Blockediniran.com. Kobeissi found out about the block on Monday, when an Iranian user told him Cryptocat had stopped working.
"I was like WTF," Kobeissi, who lives in Montreal, Canada, told Mashable in an online chat. "I honest to God don't know why they chose only Cryptocat."
Cryptocat, which is available as an app for Mac computers as well as a plugin for Chrome and Firefox, is the most well-known of the slew of new apps that bring encrypted communications to the masses. Kobeissi has received $186,000 in funding from Radio Free Asia's Open Technology Fund to develop the app.
Strangely, similar tools by Open Whisper Systems or The Guardian Project, which have also received grants from the Open Technology Fund, are not currently blocked. But, perhaps, Cryptocat was used specifically by groups that the Iranian government is targeting.
"Nadim and Cryptocat are celebrities," Collin Anderson, an independent security researcher who studies Iran, told Mashable. "It's possible that a dissent political organization was training on Cryptocat and they caught wind."
Nariman Gharib, an Iranian researcher based in London, said it would make sense for Iran to block a service like Cryptocat, even though he recognized that it isn't exactly mainstream.
"In this case, I imagine they just want to block more secure services," Gharib said. "And they send people to use other services which are not secure, so it's going to be easier for them to spy on people."
The Iranian government possesses technology to prevent access to sites like YouTube, Twitter and Facebook. When an Iranian netizen tries to go to the Cryptocat site or use its plugin, Anderson explained, the government can intercept the request for the site with Deep Packet Inspection, a technique that allows for widespread online traffic monitoring, and redirect the netizen to another site, which displays a government message like the one below.
Kobeissi has taken a few steps to circumvent the block, as he explains in both English and Farsi on Cryptocat's blog, which isn't blocked in Iran.
Iranians can still use Cryptocat through Tor, a software that allows for anonymous web browsing and circumvents filters. Also, Cryptocat now has an address on the Tor network -- most commonly referred to as the deep web. (This hidden site can be accessed using Tor at the URL: catmeow2zuqpkpyw.onion.)
Despite the block, Kobeissi sees a silver lining.
"It's actually really encouraging, I feel this proves that Cryptocat must have been making a difference and that Iran must have been having trouble spying on it," he said, adding that since he doesn't track user activity, he's not sure how many people accessed it in Iran.
Kevin Bankston, policy director of the Open Technology Institute at the New America Foundation, hopes Cryptocat will be unblocked soon because tools like it help netizens escape surveillance.
"It's a mistake to deprive the citizenry of tools that help them secure their Internet communications," he said.
This story has been amended. An earlier version of this story mistakenly indicated that the Open Technology Fund was part of the State Department. It's actually funded by Radio Free Asia.
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