A New Replay Attack Against Anonymous

Communication Networks

Xinwen Fu

April 20, 2023

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Outline Introduction Replay attack against anonymous

communication systems - Tor Evaluation Summary

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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

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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.

IntelligenceCenter

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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

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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?

BobAliceNetwork

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Outline Introduction Replay attack against anonymous

communication systems - Tor Evaluation Summary

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Basic Principle of the Replay Attack

A circuit is created by a sender and dedicated for a pair of users

circuit A circuit B circu

it C

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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

Alice BobEve 1 at Entry Eve 2 at Exit

circuit A circuit B circuit C

t t t t

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Outline Introduction Replay attack against anonymous

communication systems - Tor Evaluation Summary

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Experiment Setup

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Duplication Causing Path Teardown

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Outline Introduction Replay attack against anonymous

communication systems - Tor Evaluation Summary

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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

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Thank you!

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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.

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Replay Attack against Tor