What is Tor? • Tor was originally designed, implemented, and deployed as a third- generation onion routing project of the U.S. Naval Research Laboratory , for the primary purpose of protecting government communications. • Tor is a free tool that allows people to use the internet anonymously. • Basically, Tor protects you by bouncing your communications around a distributed network of relays run by volunteers all around the world: it prevents somebody watching your Internet connection from learning what sites you visit, it prevents the sites you visit from learning your physical location, and it lets you access sites which are blocked. • Tor anonymizes the origin of your traffic!www.sti-innsbruck.at 3
What is Tor? IP address that appears via the Tor browser IP address that appears IP address that appears via other browsers at via other browsers at the same time the same timewww.sti-innsbruck.at 4
What is under the hood? Basic knowledge from networks •Internet data packet consists of two kinds of data: – control information (header): provides data the network needs to deliver the user data (e.g. source and destination addresses, error detection codes like checksums, and sequencing information); – user data (also known as payload): whatever is being sent, whether thats an email message, a web page, or an audio file. •Even if you encrypt the data payload of your communications, traffic analysis still reveals a great deal about what youre doing and, possibly, what youre saying. Thats because it focuses on the header, which discloses source, destination, size, timing, and so on. Figure from http://www.totalsem.com/files/MMP_N_ch1.pdfwww.sti-innsbruck.at 5
What is under the hood? (cnt’d) Tor is based on Onion Routing, a technique for anonymous communication over a computer network. Steps •Messages are repeatedly encrypted and then sent through several network nodes called onion routers. •Each onion router removes a layer of encryption to uncover routing instructions, and sends the message to the next router where this is repeated. This prevents these intermediary nodes from knowing the origin, destination, and contents of the message. Onions http://en.wikipedia.org/wiki/Onion_routingwww.sti-innsbruck.at 6
What is under the hood? (cnt’d) Users software or client incrementally builds a circuit of encrypted connections through relays on the network.www.sti-innsbruck.at 7
Who is using Tor? • Normal people (e.g. protect their browsing records) • Militaries (e.g. military field agents) • Journalists and their audiences (e.g. citizen journalists encouraging social change) • Law enforcement officers (e.g. for online “undercover” operations) • Activists and Whilstblowers (e.g. avoid persecution while still raising a voice) • Bloggers • IT professionals (e.g. during development and operational testing, access internet resources while leaving security policies in place)www.sti-innsbruck.at 8
Tor project Software and Services under the Tor project umbrella: •Torbutton •Tor Browser Bundle •Vidalia •Arm •Orbot •Tails •Onionoo •Metrics Portal •Tor Cloud •Obfsproxy •Shadow •Tor2web https://www.torproject.org/projects/projects.html.enwww.sti-innsbruck.at 9
Hands on • Demo • Metrics: https://metrics.torproject.org/ http://tigerpa.ws/tor_metrics/www.sti-innsbruck.at 10
References 1. Onion Routing http://www.onion-router.net/ 2. Tor project: http://www.torproject.org 3. Roger Dingledine, Nick Mathewson, Paul SyversonTor: The Second-Generation Onion Router 4. Len Sassaman: The Faithless Endpoint How Tor puts certain users at greater riskwww.sti-innsbruck.at 11
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