It all started with an Xbox

The competition was to play Connect-4

Our programs signalled identitythrough the moves they made

Pos

sibl

e m

ove

sequ

ence

s (lo

g sc

ale)

Move number

1 2 3 4 5 6 7 8 9 10

1.0

4.7

14.2

41.4

101.2

332.9 484.0

1399.0

4001.06380.0

−

− −

−

−

− −

−

−

−

−

− −

−

−

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−

− −

51840

480

We wrote a paper for InfoHiding 2004

Following PET 2004, I operated a Tornode at Cambridge University

Our attack was to trace anonymouspaths through the network

Attacker

webserverTor NetworkVictim client

Measurer

Latency measurements showed trafficload flowing through a node

time (s)

late

ncy

(ms)

0 200 400 600 800

116.

0050

010

0015

0020

00

Induced load

Latency

We wrote a paper for Oakland 2005

Following InfoHiding 2004, I alsoinvestigated currency watermarking

I presented my results at again 21C3,and attended a talk on Nushu

Alice

Bob

Walter

Initial sequence numbers havecomplex structure

Source IP Dest. IP S. Port D. Port

R Concatenate 32 random bits

R-MD4 block: 256 random bits

Take bits 32–63

c replace top byte with rekey counter. . .. . .and add 32-bit time (µs)+T





Take bits 32–63

c replace top byte with rekey counter. . .

. . .and add 32-bit time (µs)+T





Take bits 32–63

c

replace top byte with rekey counter. . .

. . .and add 32-bit time (µs)+T

Even putting perfectly random ISNs willbe detectable

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1 2 3 4 5 6 7

1176

3000

5000

7212

Unmodified Linux

Time difference (ms)

ISN

diff

eren

ce (

mod

232

)

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0 1 2 3 4 5 6 7

1272

0000

2e+

093e

+09

4.29

3e+

09

Random ISN

Time difference (ms)

We wrote a paper on TCPsteganography for InfoHiding 2005

At Oakland 2005 I attended a talk onclock skew and security

0 100 200 300 400

020

4060

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●●●●●●●

Time (s)

Offs

et (

ms)

Clock skew changes with temperature

Time

Fri 11:00 Fri 21:00 Sat 07:00 Sat 17:00

Non

−lin

ear

offs

et c

ompo

nent

(m

s)

−−2.0

−1.5

−1.0

−0.5

0.0

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25.8

25.9

26.0

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26.4

Tem

pera

ture

(°C

)

●

Non−linear offset

De−noised

Variable skew

Temperature

We can do the same attack on Tor,measuring skew rather than latency

Attacker Tor Network Hidden Server

Measurer

Pattern measured

Pattern injected

Resulting pattern

The results show clear patterns

Time (hh:mm)

01:00 05:00 09:00

Non

−lin

ear

offs

et c

ompo

nent

(m

s)

−−4

−3

−2

−1

0

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37.5

38.0

38.5

39.0

Tem

pera

ture

(°C

)

●

From these results, I wrote my thesis

covert channel vulnerabilities in anonymity...

Documents