Tor is apparently no longer a safe place to run a marketplace for illegal goods and services. With the alleged operator of the original Silk Road marketplace, Ross Ulbricht, now going to trial, the arrest of his alleged successor and a number of others in a joint US-European law enforcement operation, and the seizure of dozens of servers that hosted "hidden services" on the anonymizing network, the operators of the latest iteration of Silk Road have packed their tents and moved to a new territory: the previously low-profile I2P anonymizing network.
On the surface, I2P (which originally was an acronym for "Invisible Internet Project") is similar in many ways to the Tor Project's anonymizing service. Like Tor, I2P encapsulates and anonymizes communications over the Internet, passing Web requests and other communications through a series of proxies to conceal the location and identity of the user. Like Tor, I2P also allows for the configuration of websites within the network that are concealed from the Internet at large. Called "eepsites," these equivalents to Tor's hidden services can only be reached by using the anonymizing network or a portal site that connects to the I2P proxy network.
But there are some significant differences between Tor and I2P beneath the surface, from the technologies they are based on to how the networks are implemented. In many ways, I2P is a much less mature technology than Tor—but it has the potential to anonymize a greater range of applications and services as it gains adoption, and its architecture is theoretically less vulnerable to the sorts of de-anonymizing attacks that some researchers have claimed to have been able to use against Tor.