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The Tor Project Our mission is to be the global resource for - - PowerPoint PPT Presentation

Jan 07, 2024 837 likes •1.45k views

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. 1 O n l i n e A n o n y

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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

  • f speech, privacy rights online, and

censorship circumvention.

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  • O

n l i n e A n

  • n

y mi t y

– O

p e n S

  • u

r c e

– O

p e n N e t w

  • r

k

  • C
  • mmu

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r e s e a r c h e r s , d e v e l

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e r s , u s e r s a n d r e l a y

  • p

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r

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  • n
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Estimated 2,000,000 to 8,000,000 daily Tor users

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Threat model: what can the attacker do?

Alice Anonymity 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!”

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Anonymity serves different interests for different user groups.

Anonymity

Private citizens Businesses “It's network security!” “It's privacy!”

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Anonymity serves different interests for different user groups.

Anonymity

Private citizens Governments Businesses “It's traffic-analysis resistance!” “It's network security!” “It's privacy!”

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Anonymity serves different interests for different user groups.

Anonymity

Private citizens Governments Businesses “It's traffic-analysis resistance!” “It's network security!” “It's privacy!” Human rights activists “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 ( B

  • b

2 , “ Z ” ) “Y” “Z” “X”

(example: some commercial proxy providers)

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But a central relay is a single point of failure.

Bob2 Bob1 Bob3 Alice2 Alice1 Alice3 Evil Relay E(Bob3,“X”) E(Bob1, “Y”) E ( B

  • b

2 , “ Z ” ) “Y” “Z” “X”

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... or a single point of bypass.

Bob2 Bob1 Bob3 Alice2 Alice1 Alice3 Irrelevant Relay E(Bob3,“X”) E(Bob1, “Y”) E ( B

  • b

2 , “ Z ” ) “Y” “Z” “X”

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

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So, add multiple relays so that no single one can betray Alice.

Bob Alice R1 R2 R3 R4 R5

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

Bob Alice R1 R2 R3 R4 R5 Bob2

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Tor's safety comes from diversity

  • #1: Diversity of relays. The more relays

we have and the more diverse they are, the fewer attackers are in a position to do traffic confirmation. (Research problem: measuring diversity over time)

  • #2: Diversity of users and reasons to use
  • it. 50000 users in Iran means almost all of

them 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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28 R4 R2 R1 R3 Bob Alice Alice Alice Alice Alice Blocked User Blocked User Blocked User Blocked User Blocked User Alice Alice Alice Alice Alice Alice Alice Alice Alice Alice

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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
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“Still the King of high secure, low latency Internet Anonymity” Contenders for the throne:

  • None
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41 R4 R2 R1 R3 Bob Alice Alice Alice Alice Alice Blocked User Blocked User Blocked User Blocked User Blocked User Alice Alice Alice Alice Alice Alice Alice Alice Alice Alice

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Arms races

  • Censorship arms race is bad
  • Surveillance arms race is worse

– And centralization of the Internet

makes it worse still

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O n i

  • n

S e r v i c e

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Onion service properties

  • Self authenticated
  • End-to-end encrypted
  • Built-in NAT punching
  • Limit surface area
  • No need to “exit” from Tor
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51 q

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S e c u r e D r

  • p

https://securedrop.org/directory

Today, 30+ organizations use SecureDrop

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R i c

  • c

h e t

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O n i

  • n

S h a r e

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Tor isn't foolproof

  • Opsec mistakes
  • Browser metadata fingerprints
  • Browser exploits
  • Traffic analysis
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How can you help?

  • Run a relay (or a bridge)
  • Teach your friends about Tor, and privacy

in general

  • Help find -- and fix – bugs
  • Work on open research problems

(petsymposium.org)

  • donate.torproject.org
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R e l a y

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  • r

m e e t u p , t

  • d

a y

1 5 : t

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a y i n r

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H . 3 2 4 4

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