1. A New Replay Attack Against Anonymous Communication Networks Xinwen Fu June 30, 2015

2. ICC08 Xinwen Fu2/15 Outline  Introduction  Replay attack against anonymous communication systems - Tor  Evaluation  Summary

3. ICC08 Xinwen Fu3/15 Internet Security  Internet has brought convenience to our everyday lives  However, it has also become a breeding ground for a variety of crimes Malicious codes (worm and viruses) caused $13.2 billions in financial losses worldwide in 2001  We need to understand these attacks and design corresponding countermeasures  We present our research on a new attack against anonymous communication systems

4. ICC08 Xinwen Fu4/15 Traditional Spy Network  Indirectly send secret to Intelligence headquarter through a number of intermediate agents.  Protect the intelligence agent (i.e., source of secret) from being identified. Intelligence Center

5. ICC08 Xinwen Fu5/15 Anonymous Communication Network - Tor  Client: the user of the Tor network  Server: the target TCP applications such as web servers  Tor router: the special proxy relays the application data  Directory server: servers holding Tor router information

6. ICC08 Xinwen Fu6/15 Problem Definition of Attacks against Tor  Alice is sending messages to Bob through encrypted and anonymous channel, how can Evil confirm the communication relationship between Alice and Bob? Bob Alice Network

7. ICC08 Xinwen Fu7/15 Outline  Introduction  Replay attack against anonymous communication systems - Tor  Evaluation  Summary

8. ICC08 Xinwen Fu8/15 Basic Principle of the Replay Attack  A circuit is created by a sender and dedicated for a pair of users circuit A circuit B circuit C

9. ICC08 Xinwen Fu9/15 Replay Attack against Tor  A packet comes from Alice through circuit A, and goes to Bob after circuit C  Replayed packet X causes a (special) decryption error at the end of circuit C at Eve 2 An AES counter is synchronized through path and disturbed The duplicated packet disrupt the counter  Therefore, Circuits A and C are created by Alice  Claim: Alice is communication with Bob … … … Bob, Message M KBKB KAKA … KnKn Alice K1K1 Bob, Message M KBKB KAKA … KnKn Alice K1K1 BobEve 1 at EntryEve 2 at Exit circuit Acircuit Bcircuit C tttt

10. ICC08 Xinwen Fu10/15 Outline  Introduction  Replay attack against anonymous communication systems - Tor  Evaluation  Summary

11. ICC08 Xinwen Fu11/15 Experiment Setup

12. ICC08 Xinwen Fu12/15 Duplication Causing Path Teardown

13. ICC08 Xinwen Fu13/15 Outline  Introduction  Replay attack against anonymous communication systems - Tor  Evaluation  Summary

14. ICC08 Xinwen Fu14/15 Summary and Future Work  We identified a new replay attack against Tor and the attack can seriously degrade anonymity that Tor provides Need only one packet!!!  Our experiments validate the feasibility and effectiveness of the replay attack  Future work: develop countermeasure against the replay attack

15. ICC08 Xinwen Fu15/15 Thank you!

16. ICC08 Xinwen Fu16/15 Traditional Spy Network  Indirectly send secret to Intelligence headquarter through a number of intermediate agents.  Protect the intelligence agent (i.e., source of secret) from being identified.

17. ICC08 Xinwen Fu17/15 Replay Attack against Tor … … … Bob, Message M KBKB KAKA … KnKn Alice K1K1 Bob, Message M KBKB KAKA … KnKn Alice K1K1