A number of sources have reported that the Iranian government has cut off access to all encrypted internet services. Iran has prevented access to services like Facebook and Twitter before, but this time the blocks appear to be particularly widespread. The Washington Post reported yesterday that access to Google services was being restricted, but a post on Hacker News this morning states that all encrypted connections like proxies and HTTP Secure sites (https://) are also being blocked. Commenters on the post have confirmed the news.
Tomorrow marks the anniversary of Iran's 1979 Islamic revolution, which saw the formation of the Islamic Republic which still stands to this day. The government appears to be restricting encrypted access to the internet to avoid a repeat of last year's events which saw a large number of people take the streets in a protest for political reform. Without a secure form of communication, it will be difficult for dissidents to organize protests without fear of retribution.