The Onion Router

How Works?

BMS College of Engineering, Bangalore

By :- ONKAR BADIGER

Overview How TOR works?

• Why use TOR?• Places of attack• Anonymity network(TOR design)• Chain of relays• Encryption • Bridges • Extensions

• https everywhere• Tor button• Noscript

Why use TOR?• Compromised ISP• Monitoring ISP• Monitored website• Monitored network• Filtered website(blocked)

ISP Destination(website)

This is how we connect to internet

ISPDestination(website)

Anonymity network

Anonymity network must be between ISP and our destination

ISPDestination(website)

Anonymity network

Places of attack

Compromised ISP(untrusted ISP)Monitored ISP

ISPDestination(website)

Anonymity network

Places of attack

Control parts of anonymity network may attack

ISPDestination(website)

Anonymity network

Places of attack

Website is monitoring to advertise, collect data

etc.

Anonymity network Proxy? VPN?

RELAY

Anonymity network Proxy? VPN?

RELAY

TRUST?

ATTACKER

ATTACKER

RELAY 1

RELAY 2

RELAY 3

ISP

TOR network

Can we trust relays?

RELAY 1

RELAY 2

RELAY 3

ISP

TOR network

What if entry/guard relay is corrupt?

RELAY 1

RELAY 2

RELAY 3

ISP

TOR network

What if exit relay is corrupt?

RELAY 1

RELAY 2

RELAY 3

ISP

TOR network

What if both entry & exit relay are corrupt?

Solution?

RELAY 1

RELAY 5

RELAY 2

RELAY 4

RELAY 3

ISP

TOR network

RELAY 7

RELAY 6 RELAY 8

RELAY 1

RELAY 5

RELAY 2

RELAY 4

RELAY 3

ISP

TOR networkKEY

KEY

KEY

Solution? ENCRYPTION

RELAY 1

RELAY 5

RELAY 2

RELAY 4

RELAY 3

ISP

TOR networkKEY

KEY

KEY

unencrypted

https everywhere

RELAY 1

RELAY 5

RELAY 2

RELAY 4

RELAY 3

ISP

TOR networkKEY

KEY

KEY unencrypte

d

How TOR manages relaying?

Tor button

Tor button

New tor circuit

Tor button is not all about relaying!

Tor button Not just relaying!

Security

Tor button Not just relaying!

Security

Bridges ?

• Entry relays

• Not listed in main TOR directory

Why use Bridges ?• ISP blocks TOR• You don’t want ISP to know that you are using TOR

Types of Bridges ?

Preconfigured bridge

Custom bridge

Tor button Not just relaying!

Network settings

Tor button Not just relaying!

Network settings

https://bridges.torproject.org/bridges@torproject.org

No script

Blocks JavaScriptBlocks javaBlacks flashBlocks other pluginsProtects against clickjacking

How TOR works?

• Why use TOR?• Places of attack• Anonymity network(TOR design)• Chain of relays• Encryption • Bridges • Extensions

• https everywhere• Tor button• Noscript

Check these out…• How to setup tor relay?• How to setup non exit tor relay?• ORBOT (TOR for android)• TAILS (live OS routed through TOR)• Pluggable transports(fakes innocent traffic)• Unblock TOR in college!

The Onion Router

Source : https://www.torproject.org/docs/documentation.html.en

ONKAR BADIGER