The Silk Road case shined a light on the deep underbelly of the web -- exposing many casual Internet users to unfamiliar terms like Deep Web, Tor and Bitcoin. So we asked Johns Hopkins cryptography professor Matthew Green -- who recently was in the news himself for his writings on the NSA -- to help break down this shadowy virtual world for our readers.

Q: What exactly is Deep Web?


The Deep Web means two things. In some cases it's used to refer to the part of the web that isn't reached by search engines. Second, and more relevant to this case, it refers to a series of web sites that are only accessible through the Tor anonymity service.

Tor is software that routes your web connections through a number of other web servers -- possibly around the world -- in order to hide the source and destination of the connection. Typically you use Tor to access normal web sites, with the guarantee that the website can't trace you. However Tor also allows the destination web site to be in an anonymous location, also known as a "Tor Hidden Service".

Thus in the second usage, the Deep Web is the name people give to the part of the web that's made up only of Tor hidden services. This is a pretty strange bunch of sites, including Silk Road (up until Wednesday) and some other legal and illegal services. It's an interesting place.

Q: How do you use Deep Web? Do you need special equipment?

You need Tor, which is software you can download from It runs on any standard computer. The Tor Browser Bundle is a one-click install that gives you a web browser and the software for starting up the connections.

Once you've got that installed all you need is the address of the site. This looks like a normal web URL but ends in ".onion". You put this into the browser like any other site. Silk Road used to be at "silkroadvb5piz3r.onion".

Q: Deep Web is in the news this week because of the Silk Road case, but does Deep Web have other uses and what are they?

There are all sorts of things in there: search engines, email services, political sites. And child porn. And Silk Road.

There are a bunch of sites out there. This list gives some of them.

Q: What is Bitcoin and do you think it could ever go mainstream?

Bitcoin is a digital currency that was invented in 2009 by an anonymous gentleman named "Satoshi Nakamoto" (probably not his real name). Bitcoins are digital information constructed by very powerful computers and shared over a network. They have no intrinsic value except for the fact that they're very expensive to make and have a limited supply (25 Bitcoins are created every 10 minutes, but the total number of coins will never exceed 20 million or so).

The nice thing about Bitcoin is that it's incredibly easy to send Bitcoin to someone anywhere in the world without having to go through a service like Paypal. The value of Bitcoin has gone from about zero to upwards of $200 per coin, settling somewhere in the middle.

Bitcoin is actually very easy to use thanks to a bunch of new services like Coinbase that make it easy to buy and spend coins. About the most difficult problem is the need to trade money for Bitcoin, which can be a bit of a hassle. Yes, adoption has exploded and will likely start to pick up steam with 'average people' since it's a very convenient way to pay people.