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  1. I was wondering how Torbutton and Tor change IP when browsing internet using Firefox?
  2. I learned that using proxy can change IP to be the IP of the proxy server. But is the way by Torbutton and Tor the same as using a proxy?
  3. With Torbutton and Tor, why is IP only changed when browsing internet using Firefox, and not changed outside Firefox, such as using a different browser application?
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I was wondering how Torbutton and Tor change IP when browsing internet using Firefox?

Torbutton does not change anything. It just tells Firefox to use Tor.

When you use a proxy server, the browser sends all your HTTP requests to that server, which forwards them to their final destination.

  • browser ↔ proxy server ↔ web server

Your actual address is not changed, it's only disguised, because the web server only sees what connected to it directly – in this case, the proxy.

(However, if someone takes control over the proxy, they can monitor everything sent through it (such as who uploaded files to Site X). Often, it's the server's owner themselves.)

With Tor, the request is routed through several servers, and encrypted separately for each:

  • browser ↔ Tor on your computer

  • Tor on your computer [[[↔]]] node A [[↔]] node B [↔] node C ↔ web server

    (Each [ ] represents a layer of encryption.)

This way, the web server only sees a connection coming from node C, while C only sees a connection from B. Only node A knows where the user is, but it doesn't know what the user is transferring.

(This is called onion routing. See also Tor Overview.)


I learned that using proxy can change IP to be the IP of the proxy server. But is the way by Torbutton and Tor the same as using a proxy?

Tor is a proxy, but it works in a different way than the "proxy servers" you're used to. See description above.

Torbutton, again, is only a button that reconfigures Firefox.


With Torbutton and Tor, why is IP only changed when browsing internet using Firefox, and not changed outside Firefox, such as using a different browser application?

Torbutton is a Firefox add-on and is only able to reconfigure Firefox. Tor does not change any settings itself – when you start it, it only waits for connections. You yourself have to tell programs to connect through it.

If the program supports using a SOCKS 5 proxy server, point it to 127.0.0.1:9050. If it only supports HTTP proxies, you'll need Polipo, which comes with the Tor Bundle, and runs at 127.0.0.1:8123.

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I've been using tor for years and couldn't have summarized it that well. –  Blomkvist May 5 '11 at 16:46
    
@grawity: Thanks! I observe that the ip selected by Tor changes constantly, and I am not aware that my internet connection disconnect and reconnect. So does it mean Tor changes ip automatically for the same internet connect session? –  Tim May 5 '11 at 19:21
    
@Tim: Yes, when you connect through Tor, it builds new circuits every so often, to avoid being tracked. (If you installed the Tor/Vidalia bundle, you can see this in Vidalia's "Network Map".) By the way, this has got absolutely nothing with your "real" Internet connection. Tor doesn't touch it in any way. –  grawity May 5 '11 at 20:28
    
...by which I mean Tor doesn't change it in any way, only uses it like any other program would. –  grawity May 5 '11 at 20:39
    
@grawity: Thanks! (1) Will constantly changing ip make the fact of hiding ip obvious? Is it possible to fix an ip? (2) How does Tor find so many proxies, while it is not easy to find them by myself? –  Tim May 5 '11 at 22:03

1.)You're really asking how oinion routing works which is incredibly complex and beyond the scope of this site. Here's a good summary.

http://www.addictivetips.com/internet-tips/what-is-tor-project-and-how-tor-works-complete-guide/

2.) It's not the same as a proxy although it does use proxy services

3.) tor doesn't proxify everything by default. You need to set up each app to use it.

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The Tor site actually has a pretty good description of how onion routing works. Essentially each Tor node encapsulates the requests that it receives and forwards the encapsulated request to the next node.

The ability of Tor to hide originating source addresses from the destination server is dependant on the traffic that is being passed. In general, the destination server will see the IP address of the last hop Tor node; however this is not always the case. For example, a website might embed some Javascript that submits the local IP address into some form data.

Only the applications that are configured to use Tor a proxy will benefit.

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