

by on November 10, 2009 · 11 comments

By Eric Beach and Adam Marcus

In the previous entry in the Privacy Solutions Series, we described how privacy-sensitive users can use proxy servers to anonymize their web browsing experience, noting that one anonymizer stood out above all others: Tor, a sophisticated anonymizer system developed by the Tor Project, a 501(c)(3) U.S. non-profit venture supported by industry, privacy advocates and foundations, whose mission is to “allow you to protect your Internet traffic from analysis.” The Torbutton plug-in for Firefox makes it particularly easy to use Tor and has been downloaded over three million times. The TorBrowser Bundle is a pre-configured “portable” package of Tor and Firefox that can run off a USB flash drive and does not require anything to be installed on the computer on which it is used. Like most tools in the Privacy Solutions series, Tor has its downsides and isn’t for everyone. But it does offer a powerful tool to privacy-sensitive users in achieving a degree of privacy that no regulation could provide.

Why Use Tor?



(2) Blocking of Internet traffic based upon content analysis. Rather than simply relying on website blacklists, many countries use content-based filtering to prevent individuals from seeking out information deemed undesirable. For example, the Chinese government censors searches for “falun gong” through packet inspection and analysis.


(4) Government monitoring. With the United States government’s pervasive surveillance of the electronic activities of Americans, some citizens understandably desire to protect their First Amendment right to anonymously send and receive information-i.e., without the government being able to determine their identity.

How Tor Works

The general web data flow online looks something like this:

As we mentioned in our piece about anonymizers, a sophisticated anonymizer can obscure the identity of any one web user by pooling requests from large numbers of users across a “daisy chain” of proxy servers-thus effectively anonymizing the user’s identity, like so:

Tor works somewhat differently: Rather than simply trying to achieve “anonymity in a crowd” (of other web users using the network), Tor’s “client software” (e.g., TorButton) picks a random path through a network of other “Tor nodes” (users of Tor) for every request sent from the user’s computer. As the Tor Project explains:


Tor thus achieves a high degree of anonymity, relying “not on the trustworthiness of individual servers but rather on the network design, which prevents a given router from knowing both the origin and the destination or even which other routers it would need to cooperate with to get that information.”

The following chart from the Tor Project’s more extensive explanation conveys the basics:

How to Install Tor


The Tor Project also offers TorBrowser, an all-in-one bundle of the portable edition of Firefox (which can be carried along with all its settings on a USB stick or CD) pre-configured with the Tor plug-in. There is also a version of TorBrowser that includes the Pidgin instant messaging client, for those who also want to protect their instant messaging. Set-up takes less than three minutes and is just the thing for those trying to stay “one step ahead of The Man.” For more help on how to install the TorBrowser, click here or here.

Downsides/Risks of Tor


  2. Tor encrypts the data between the intermediary nodes.



Time for Direct Access

Time for Tor Access

28.1 seconds

188 seconds

2.2 seconds

9.34 seconds

1.89 seconds

7.5 seconds

15.87 seconds

74 seconds



Increased Vulnerability. The second major downside is that the exit-node could record your data or perform a number of malicious attacks, as explained by Ars Technica and As the Berkman Center’s 2007 Circumvention Report noted, “Tor provides strong anonymity only if the user is careful to submit data to HTTPS protected servers.” If you plan to use Tor, you should consult the following Tor security warnings:

  • REMARK(S) ABOUT USING CONFIDENTIAL DATA ON (INSECURE) NON-HTTPS/SSL-CONNECTIONS: If you’re planning to visit password protected sites on non-encrypted connections, keep in mind that some exit-nodes record the passwords and possibly use them for abuse. Also all other transferred data is possibly recorded and misused.
  • REMARK(S) ABOUT ACCESSING ELECTRONIC BANKING AND OTHER SENSITIVE SITES VIA TOR: Most banks and similar institutions (PayPal for example) are using extended fraud countermeasures, like IP-origin plausibility checks and anonymous server blacklistings. Therefore you risk getting your bank account locked for security reasons by using the Tor-network.
  • REMARK(S) ABOUT (SECURE) HTTPS/SSL-CONNECTIONS TO FRAUD CRITICAL SITES: If you’re planning to visit fraud critical HTTPS/SSL-secured sites (Banks for example) and that specific site is querying you unexpectedly about accepting a new SSL-Certificate, be highly alert. Check the Certificate data or try another EXIT-node first. There are some rumors around, that some EXIT-nodes are trying to fake/highjack such HTTPS/SSL-connections.

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