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The Tor Project

Our mission is to be the global resource for technology, advocacy, research and

education in the ongoing pursuit of freedom of speech, privacy rights online, and

censorship circumvention.

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● Online Anonymity– Open Source– Open Network

● Community ofresearchers,developers, users andrelay operators.

● U.S. 501(c)(3) non-profit organization

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Estimated 2,000,000+ daily Tor users

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Threat model:what can the attacker do?

AliceAnonymity network Bob

watch (or be!) Bob!

watch Alice!

Control part of the network!

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Anonymity isn't encryption: Encryption just protects contents.

Alice

Bob

“Hi, Bob!”“Hi, Bob!” <gibberish>

attacker

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Anonymity serves different interests for different user groups.

Anonymity

Private citizens“It's privacy!”Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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Anonymity serves different interests for different user groups.

Anonymity

Private citizens

Businesses

“It's network security!”

“It's privacy!”Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

reposting of these slides is expressly prohibited.

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Anonymity serves different interests for different user groups.

Anonymity

Private citizens

Governments Businesses

“It's traffic-analysisresistance!”

“It's network security!”

“It's privacy!”Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

reposting of these slides is expressly prohibited.

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Anonymity serves different interests for different user groups.

Anonymity

Private citizens

Governments Businesses

“It's traffic-analysisresistance!”

“It's network security!”

“It's privacy!”

Human rightsactivists

“It's reachability!”

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The simplest designs use a single relay to hide connections.

Bob2

Bob1

Bob3

Alice2

Alice1

Alice3

Relay

E(Bob3,“X”)

E(Bob1, “Y”)

E(Bob2, “Z”)

“Y”

“Z”

“X”

(example: some commercial proxy providers)

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But a central relay isa single point of failure.

Bob2

Bob1

Bob3

Alice2

Alice1

Alice3

EvilRelay

E(Bob3,“X”)

E(Bob1, “Y”)

E(Bob2, “Z”)

“Y”

“Z”

“X”

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... or a single point of bypass.

Bob2

Bob1

Bob3

Alice2

Alice1

Alice3

IrrelevantRelay

E(Bob3,“X”)

E(Bob1, “Y”)

E(Bob2, “Z”)

“Y”

“Z”

“X”

Timing analysis bridges all connections through relay ⇒ An attractive fat target

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So, add multiple relays so thatno single one can betray Alice.

BobAlice

R1

R2

R3

R4 R5

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Alice makes a session key with R1...And then tunnels to R2...and to R3

BobAlice

R1

R2

R3

R4 R5

Bob2

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15Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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16Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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Tor's safety comes from diversity

● #1: Diversity of relays. The more relayswe have and the more diverse they are,the fewer attackers are in a position to dotraffic confirmation. (Research problem:measuring diversity over time)

● #2: Diversity of users and reasons to useit. 50000 users in Iran means almost all ofthem are normal citizens.

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Transparency for Tor is key

● Open source / free software● Public design documents and

specifications● Publicly identified developers● Not a contradiction:

privacy is about choice!

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But what about bad people?

● Remember the millions of daily users.● Still a two-edged sword?● Good people need Tor much more

than bad guys need it.

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20Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or reposting of these slides is expressly prohibited.

21Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or reposting of these slides is expressly prohibited.

22Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

reposting of these slides is expressly prohibited.

300000 -

200000 -

100000 -

o-

'

Mar-2015

Directly connecting users from Russia

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Jun-2015 I

Sep-2015 I

Dec-2015

The Tor Project - https://metrics.torproject.org/

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Mar-2016

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R4

R2

R1

R3

Bob

Alice

Alice

Alice

Alice

Alice

BlockedUser

BlockedUser

BlockedUser

BlockedUser

BlockedUser

Alice

AliceAlice

Alice

Alice

Alice

Alice

Alice

AliceAlice

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Directly connecting users from the Islamic Republic of Iran

12000-

10000-

8000-

6000-

4000-

2000-

0-

1

Dec-2010 I

Jan-2011 I

Feb-2011 I

Mar-2011

The Tor Project - https://metrics.torproject.org/

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Apr-2011

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Pluggable transports

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Pluggable transports

● Flashproxy (Stanford), websocket● FTEProxy (Portland St), http via regex● Stegotorus (SRI/CMU), http● Skypemorph (Waterloo), Skype video● uProxy (Google), webrtc● ScrambleSuit (Karlstad), obfs-based● Telex (Michigan/Waterloo), traffic divert

Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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28Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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29Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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30Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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31Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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32Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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33Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or reposting of these slides is expressly prohibited.

34Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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35Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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36Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or reposting of these slides is expressly prohibited.

37Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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“Still the King of high secure,low latency Internet Anonymity”

Contenders for the throne:● None

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R4

R2

R1

R3

Bob

Alice

Alice

Alice

Alice

Alice

BlockedUser

BlockedUser

BlockedUser

BlockedUser

BlockedUser

Alice

AliceAlice

Alice

Alice

Alice

Alice

Alice

AliceAlice

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40Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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41Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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Arms races● Censorship arms race is bad● Surveillance arms race is worse

– And centralization of the Internetmakes it worse still

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43Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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Onion Service

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45Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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46Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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47Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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48Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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49Note: All slides are made public by the authors who created the slides. The slides may be downloaded for informational purposes only. The reproduction, reuse or

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SecureDrop

https://securedrop.org/directory

Today, 30+ organizations use SecureDrop

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Ricochet

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Tor isn't foolproof

● Opsec mistakes● Browser metadata fingerprints● Browser exploits● Traffic analysis

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ooni.torproject.org

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explorer.ooni.torproject.org

● I

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