Voip tracing
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VoIP Tracing. Active De-anonymization of Streams. Timing Attacks [LRWW ’04]. “Normal” flows e.g. HTTP, FTP, SSH Think times dominate Very easy to do timing analysis Constant rate flows 10 pkts/sec = 1 pkt. every 0.1 sec All streams look the same Correlations are poor dropped pkts help.

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VoIP Tracing

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Voip tracing

VoIP Tracing

Active De-anonymization of Streams


Timing attacks lrww 04

Timing Attacks [LRWW ’04]

  • “Normal” flows

    • e.g. HTTP, FTP, SSH

    • Think times dominate

    • Very easy to do timing analysis

  • Constant rate flows

    • 10 pkts/sec = 1 pkt. every 0.1 sec

    • All streams look the same

    • Correlations are poor

      • dropped pkts help


Voip tracing

VoIP

  • Similar to constant rate

    • high rate of pkts (every 20 or 30 ms)

    • steady flow

    • no “think times”

  • Thus

    • hard to do end-to-end timing analysis


Key results

Key Results

  • ?


A simple idea

A

B

C

X

Y

Z

Trent’s Anonymity Service

A Simple Idea


Caveats

Caveats

  • VoIP

    • time-critcal

    • Why do we care if we degrade the phone service of the terrorists?


Watermarking

Watermarking

  • No DRM

    • 1. Alice sells a song online

    • 2. Mallory & many others buy the song

    • 3. Mallory puts the song on Kazaa

    • 4. Alice gets angry

      • But doesn’t know who did it


Watermarking1

Watermarking

  • DRM

    • 1. Alice sells a song online

      • Each copy has a special, hard-to-see, hard-to-remove “stamp”

    • 2. Mallory & many others buy the song

    • 3. Mallory puts the song on Kazaa

    • 4. Alice gets angry

    • 5. Alice checks the stamp

    • 6. Mallory goes to jail


Watermarking packets

Watermarking Packets

  • Content-based

    • Embed the stamp in the data

      • Ideally based on a key

    • Very hard to remove the stamp

      • unless you have a key

  • Cannot change the packet

    • Why not?

  • What can you change?


Algorithm

Algorithm

  • Select about 2r packets at random

    • independently selected

  • Select a distance d

  • Look at delays

    • between packet x and x+d

  • Split the 2r delays into two sets

    • A and B


Algorithm 2

Algorithm 2

  • The differences should be zero

    • A(i) - B(j) = 0, on average

    • The actual value is a random variable

    • distribution: symmetric, centered on 0

      • redundancy: number of differences used

  • Embedding the “stamp”

    • increase or decrease the average

    • which one = which bit (0 or 1)


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