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Tor the onion router



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  • 1. Tor – The Onion Router Presented By Ashly Liza Philip S5 MCA Roll No. 06 MACE
  • 2. Privacy in public networks  Internet is designed as a public network.  Routing information is public.  Encryption does not hide identities.  Prone to „traffic analysis‟
  • 3. Contd.. Internet data packet Header Data payload Source, Whatever being sent destination, time Encryption can‟t Hidden by hide encryption
  • 4. What is Anonymity?  State of being not identifiable within a set of subjects.  Unlink-ability of action and identity  Unobserve-ability (hard to achieve)
  • 5. Applications of Anonymity Privacy Untraceable electronic mail Law enforcement and intelligence Anonymous electronic voting Censorship-resistant publishing
  • 6. Anonymous networks PipeNet Garlic Routing Onion Routing Anonymizer Crowds Java Anon Proxy
  • 7. Onion Routing  By David Goldschlag, Michael Reed, Paul Syverson  ONION; special data structure.  Uses public key cryptography  Hides source and destination  Anonymize TCP-based applications  Protects anonymity of a user over network  Resistant to eavesdropping and traffic analysis
  • 8. Working of Onion Routing Uses an Onion Proxy Routes data randomly A router knows only its predecessor and successor No correspondence between data layers Different onion at each hop
  • 9. R R4 R R R3 R1 R R Alice R2 R Bob Sender chooses a random sequence of routers -Some routers are honest, some controlled by attacker -Sender controls the length of the path slide 9
  • 10. Decrypting an Onion
  • 11. Contd..
  • 12. Tor – Implementation of Onion Routing  TOR stands for „The Onion Router.‟  Second generation onion router.  Low-latency anonymous network  By Paul Syverson, Nick Mathewson, Roger Dingledine in 2004  Maintained by Free Haven Project  Hundreds of nodes on all continents
  • 13. Contd..  “Easy-to-use” client proxy  Freely available  Supports only TCP  Uses SOCKS interface  No observer can tell where data comes from/going
  • 14. Advancements over Onion Routing Perfect forward secrecy Variable exit policies Directory servers Leaky-pipe circuit topology End-to-end integrity checking SOCKS interface
  • 15. How Tor works? Same as Onion Routing Uses Diffie-Hellman key exchange Distributes data over several places Takes random pathway Used with Privoxy
  • 16. Tor Circuit Each circuit shared by multiple TCP streams Circuit created preemptively Can recover from failure
  • 17. Circuit setup Built from entry point one step at a time Circuit ID is chosen randomly Diffie-Hellman process initiated Negotiate a symmetric session key Circuit extension and Relay packet
  • 18. Tor Circuit setup(1) Client proxy establish a symmetric session key and circuit with Onion Router #1
  • 19. Tor Circuit setup(2) Circuit extension
  • 20. Tor Circuit setup(3) Client proxy extends the circuit by establishing a symmetric session key with Onion Router #3
  • 21. Using circuit
  • 22. Cells in Tor Cell (512bytes) Header Payload CircID Data Command
  • 23. Contd.. Based on commands in cells:- Control cells Relay cells Cells
  • 24. Commands in cells Control cells Relay Cells • -padding • - relay data • -create/created • -relay begin • -destroy • -relay end • -relay connected • -relay teardown • -relay connected • -relay extend/extended • -relay truncate/truncated
  • 25. E.g. Fetching a webpage
  • 26. Congestion controlOR keeps track of PACKAGE WINDOW &DELIVERY WINDOW • Window initialized to 1000cells • Decremented accordingly Circuit throttling • Forward nothing on reaching 0 • Window initialized to 500cells • Use relay sendme cells Stream throttling • Incremented on receiving relay sendme
  • 27. Hidden services Allow location hidden services Both end-points remain anonymous Both parties connect via a third party, the rendezvous point Introduction points act as contact points Server can be operated from inside a firewall
  • 28. Creating and connecting to aLocation hidden service
  • 29. Attacks on Tor Passive attacks Active attacks Attacks against Rendezvous points Directory attacks
  • 30. Users of Tor Law Militaries enforcement Bloggers officers Journalists High profile Activists and audience people NGO‟s
  • 31. Weaknesses End-to-end Slow network Illegal use correlation
  • 32. Real world deployment The Tor download page.
  • 33. The Tor/Privoxy installer.Tor in the Windows system tray.
  • 34. Setting up a proxy for Internet ExplorerThe Tor detector
  • 35. Future enhancements Usability and Integration Scalability Caching at exit nodes
  • 36. Conclusion Tor becomes most widely used anonymous network with its speed Tor supports mutual anonymity with the help of Rendezvous Point Tor resists local adversary effectively Tor anonymizes TCP streams, providing a high- throughput and low-latency network compared to the onion routing