The Tor Project

So you have a message you want to send over the internet, but you don't trust your internet service provider (ISP). Maybe you're a political activist, or a criminal, whatever. If your ISP finds out, they'll tell the police, and the police will come and arrest you.

There are a bunch of people across the world who have keys to lock-boxes, and any lock-box can fit inside any other lock-boxes. Now you pick three of these people, Alice, Bob, and Chuck to relay your message.

First, you put your message in a lock-box that only Chuck has the key to. Then you put that lock-box in another lock-box that only Bob has the key to. Then you put THAT lock-box in another lock-box that only Alice has a key to. Then you pass the whole thing off to Alice.

Alice unlocks the outermost box and sees that the inner box can only be unlocked by Bob. So she sends it to Bob. Bob unlocks the box and realizes that the inner box can only be unlocked by Chuck, so he sends it to Chuck. Chuck then unlocks the box and sees that the message is going to Google (or whoever) and sends the message. If Google responds, it'll respond directly to Chuck. Then Chuck sends the response in a similar lock-box manner to Bob who then sends it to Alice who then sends it to you.

The idea is that in this chain of communications, no ISP (or country even) has full control. You and Alice might live in China, but Bob might be in Europe, and Chuck might be in the USA. If the Chinese authorities tap into your internet connection all they'll see are these lock-boxes going between you and Alice and Alice and Bob, but they don't have enough power to arrest all of the people with all of the keys, so they can't see any of the messages that are being sent or where the messages are actually ending up. (Although they can see that SOMETHING was sent).