Anonymity With Tor - The Onion Router

72 Pages·2012·1.7 MB·English

Anonymity With Tor
The Onion Router
Nathan S. Evans Christian Grothoff
TechnischeUniversit¨atMu¨nchen
July 5, 2012
“It’s a series of tubes.” – Ted Stevens
Overview
(cid:73) What is Tor?
(cid:73) Motivation
(cid:73) Background Material
(cid:73) How Tor Works
(cid:73) Hidden Services
(cid:73) Attacks
(cid:73) Specific Attack
(cid:73) Summary
What is Tor?
(cid:73) Tor is a P2P network of Chaum inspired low-latency mixes
which are used to provide anonymous communication between
parties on the Internet.
What is Tor?
(cid:73) Sender anonymity for low latency applications
(cid:73) Common usage: Web browsing
(cid:73) Sender anonymity
(cid:73) Web server cannot identify client
(cid:73) Advanced usage:
(cid:73) Hidden services (send/receive anonymity)
(cid:73) Filesharing
(cid:73) IRC
(cid:73) Any application that communicates using TCP
⇒ Tor provides users with a service that effectively hides their
identity on the Internet.
Motivation
(cid:73) Internet packets travel from A to B transparently
(cid:73) A knows B, and B knows A (by IP address)
(cid:73) Routers, etc. can determine that A and B are communicating
(cid:73) This may reveal unintended information (e.g. person X’s
bank)
(cid:73) Encryption
(cid:73) For example, TLS (HTTPS)
(cid:73) Provides Data anonymity
(cid:73) Does not hide routing information
Motivation - Routing Example
10.0.0.1
www.google.com
Review: Mixing
David Chaum’s mix (1981) and cascades of mixes are the
traditional basis for destroying linkability:
Review: Mixing
David Chaum’s mix (1981) and cascades of mixes are the
traditional basis for destroying linkability:
Onion Routing
(cid:73) Multiple mix servers
(cid:73) Subset of mix servers chosen by initiator
(cid:73) Chosen mix servers create “circuit”
(cid:73) Initiator contacts first server S , sets up symmetric key K
1 S1
(cid:73) Then asks first server to connect to second server S ; through
2
this connection sets up symmetric key with second server K
S2
(cid:73) ...
(cid:73) Repeat with server S until circuit of desired length n
i
constructed
Onion Routing Example
(cid:73) Client sets up symmetric key K with server S
S1 1
Exchange
KS
1
Client S S
1 2