TOR http://www.torproject.org/<br />The Onion Router (TOR)<br />"Anonymity loves company [...] it is not possible to be anonymous alone“ – Roger Dingledine<br />Hundreds > 700 of volunteers run their machines as TOR nodes around the world<br />> 200,000 active users per week<br />Typically 3 nodes used for each route<br />Bandwidth < 100MB/s<br />TOR nodes are TOR onion routers<br />Roger Dingledine – <br />many presentations on youtube<br />
Alice wants to communicate with Bob<br />Alice gets a directory listing from a central server of TOR nodes<br />Directory server keys ship with the code<br />http://www.iusmentis.com/society/privacy/remailers/onionrouting/<br />
Alice randomly chooses 3 nodes and uses public-key cryptography to set up the channel<br />The process is similar to Mix net<br />entry node<br />
Once the communication channel is established, the data is moved with symmetric keys <br />TOR supports real-time communication <br />exit node<br />
TOR changes the route periodically (e.g., every 10 minutes) to avoid traffic analysis<br />
Some security analysis <br />Each TOR node routes messages for many hosts<br />It is difficult to keep track of how messages are routed within TOR network <br />Assuming majority of TOR nodes are not corrupted or collude<br />However, there are some issues in a stronger adversary model:<br />All TOR nodes are semi-honest, so entry/exit nodes know something about Alice and Bob<br />
However, attacker may know who initiates or receives the traffic<br />Entry node<br />Knows Alice starts<br />Some communication <br />Attacker<br />Knows Alice starts<br />Some communication <br />Exit node<br />Knows Bob is the <br />receiver <br />
Solution: for Alice and Bob to become TOR nodes as well<br />
Resources regarding TOR and onion routing<br />http://www.onion-router.net/<br />Download TOR at https://www.torproject.org/<br />http://www.freehaven.net/~arma/cv-pres.html<br />How TOR helps whistleblowers? --Hidden service <br />E.g., wikileaks http://gaddbiwdftapglkq.onion/<br />Paul Syverson NRL, onion routing inventor<br />
TOR location hidden service <br />Alice can connect to Bob's server without knowing where it is or possibly who he is<br />Server needs to <br />Be accessible from anywhere<br />Resist censorship<br />Require minimal redundancy for resilience in denial of service (DoS) attack<br />Can survive to provide selected service even during full blown distributed DoS attack <br />Resistant to physical attack (you can't find them)<br />How is this possible?<br />
Basic ideas of hidden services<br />Use an intermediary to marry client and server<br />Similar ideas used in Skype as well <br />For users behind NAT (network address translator) <br />
2’. Alice obtains Service Descriptor (including Intro Pt. address) at Lookup Server<br />http://www.freehaven.net/~arma/cv-pres.html<br />
4. Alice sends RP addr. and any authorization through IP to Bob<br />
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