1. Bruce Maggs relying on materials from http://www.torproject.org
Tor
Bruce Maggs
relying on materials from

3. How Tor Works
(directory server)

4. How Tor Works

6. Encryption Keys in TOR
Each relay has a long-term ``identity’’ public/private key pair used to sign TLS certificates (public keys signed by directory)
Medium-term (one week) public/private ``onion’’ keys are used to decrypt requests to extend circuits – so first node can’t spoof the whole path. These keys are deleted so that if relay is compromised, old traffic can’t be decrypted.
Short-term “connection” or “ephemeral” shared private keys are used to encrypt connections.

7. How Tor Works

8. Bridge Relays (a.k.a. Bridges)
Some ISPs/governments block all traffic to relays that appear in the Tor directory.
Bridges are relays that don’t appear in the directory.
User has to solve the problem of finding a bridge.

9. Solve a Captcha to get Bridge Address

11. Growth of Tor Network

12. Growth of Tor Network

13. Spike in Number of Users

14. Possible Explanation for Spike
Botnet “Mevade.A” a.k.a. “Sefnit” a.k.a. “SBC” is using Tor for connectivity

16. Tor Exit Nodes See Plaintext!

17. Timing Attacks
Attacker controls both an entry node and an exit node (or routers nearby)
Attacker controls inter-packet delays or throughput as traffic enters an entry node
Attacker looks for same pattern at exit node

18. Tor Browser

19. Tor Browser

21. Tor-Aware Web Servers
Connect directly to Tor, do not advertise their network addresses.

22. Establishing a Hidden Service

23. Establishing a Hidden Service

24. Finding a Hidden Service

25. Contacting a Hidden Service

26. Contacting a Hidden Service

27. Communicating with a Hidden Service

28. Using Tor as a SOCKS5 Proxy
Can tunnel any TCP connection through Tor (and DNS requests)
First run the Tor browser, it will also act as a SOCKS5 proxy and accept connections
Configure your application, e.g., chat, to use as SOCKS5 proxy

29. Configure HexChat to use Proxy

30. Now Chatting through Tor

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