Onion Routing Averts Prying Eyes

[R. A. Hettinga]

<http://www.wired.com/news/print/0,1294,64464,00.html>

Wired News


Onion Routing Averts Prying Eyes 
By Ann Harrison?

Story location: http://www.wired.com/news/privacy/0,1848,64464,00.html

02:00 AM Aug. 05, 2004 PT

Computer programmers are modifying a communications system, originally
developed by the U.S. Naval Research Lab, to help Internet users surf the
Web anonymously and shield their online activities from corporate or
government eyes.

 The system is based on a concept called onion routing. It works like this:
Messages, or packets of information, are sent through a distributed network
of randomly selected servers, or nodes, each of which knows only its
predecessor and successor. Messages flowing through this network are
unwrapped by a symmetric encryption key at each server that peels off one
layer and reveals instructions for the next downstream node.


 In contrast, messages traveling across the Internet are generally not
encrypted, and the path of a message can be seen easily, linking users to
activities like website visits.

 The Navy is financing the development of a second-generation onion-routing
system called Tor, which addresses many of the flaws in the original design
and makes it easier to use. The Tor client behaves like a SOCKS proxy (a
common protocol for developing secure communication services), allowing
applications like Mozilla, SSH and FTP clients to talk directly to Tor and
route data streams through a network of onion routers, without long delays.

 Onion routing does not guarantee perfect anonymity. But it helps protect
users from eavesdroppers who aren't watching both the initiator and
recipient of the message at the time of the transaction. Developers say Tor
can be used to prevent websites from tracking their users; block
governments from collecting lists of website visitors; protect
whistleblowers; and circumvent local censorship by employers, ISPs or
schools that restrict access to certain online services.

 The Navy is financing Tor because it wants to hide the identity of
government employees who have long used anonymous communications systems
for intelligence gathering and politically sensitive negotiations.

 "The point of the Tor system is to spread the traffic over multiple points
of control so that no one person or company has the ability to link
people," said programmer Roger Dingledine. Dingledine and Nick Mathewson,
both based in Boston, are building Tor as a research platform with a
worldwide community of open-source software developers.

 Their goal is to blend together a wide range of users and avoid the
weakness of many anonymizing services that are located on a handful of
machines and vulnerable to a single point of failure.

 Companies could also use Tor for discreet competitive research, said
Dingledine, or to route their employees' Web browsing so employment sites
like Monster can't determine which of them are trolling for a job. "Plenty
of people don't want their source IP listed in Web logs, especially .mil or
.gov visitors," said Dingledine.

 The security of the Tor service is proportional to the number of nodes in
the system. Tor is slowly scaling and looking for tens of thousands of
participants who can provide enough nodes to prevent the service from being
compromised by what the project website describes as "curious telcos and
brute-force attacks."

 "The current Tor version very effectively builds on 20 years of
development in anonymous designs," said cryptographer David Chaum, whose
1981 paper on untraceable e-mail, return addresses and digital pseudonyms
set the groundwork for the Tor service.

 Tor is distributed as free software under the commonly used 3-clause BSD
license. About 1,000 users (it's an anonymous network, so developers aren't
exactly sure) are running the service in client or server mode.

 The Tor network currently includes 35 servers that forward each data
stream at least three times. Each server averages 10 Kbps of bandwidth.
Those with reliable Internet connections, who can support at least 1 Mbps
in both directions, are being recruited as potential servers in the network.

 Users are permitted to operate an unrestricted number of nodes. But
Dingledine pointed out that a well-funded adversary could sign up for a
large number of servers and potentially take over the network.

 Those who want to operate Tor routers must therefore convince the Tor
directory server operators that they are trustworthy and reliable.
Dingledine said developers are trying to find ways to scale the system
without having to have a human check the integrity of every new server that
becomes part of the network.

 Dingeldine said the developers of another online anonymity project, called
JAP, were forced by the German government to insert a backdoor into the
program and were barred from revealing it. If anyone insisted on similar
measures for Tor, Dingledine said the community of open-source developers
who analyze source-code changes for each Tor revision would expose it -- as
they did with JAP.

 "The reason Tor works is that it's free and available software," said
Dingledine. "If it was a closed source or a proprietary system, there is no
way to know."



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R. A. Hettinga <mailto: rah at ibuc.com>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'

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