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Tor:
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Next-generation Onion Routing
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Roger Dingledine
Nick Mathewson
Paul Syverson
%%The Free Haven Project
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%%http://freehaven.net/
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Low-latency anonymity system
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Deployed: 19 nodes, hundreds of users (?)
Many improvements on earlier design
Free software -- available source code
Design is not covered by earlier onion routing
patent
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Perfect forward secrecy
Telescoping circuit
negotiates keys at each hop
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%%Separation from "protocol cleaning"
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No mixing, padding, traffic shaping (yet)
Please show us they're worth the usability tradeoff
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%%Many TCP streams can share one circuit
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Congestion control
Simple rate limiting
Plus have to keep internal nodes from overflowing
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Directory servers
Approve new servers
Tell clients who's up right now
plus their keys, location, etc
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Variable exit policies
Each server allows different outgoing connections
E.g. no servers allow outgoing mail currently
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End-to-end integrity checking
In previous onion routing, an insider could change
the text being transmitted:
"dir" => "rm *"
Even an external adversary could do this!
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Rendezvous points
allow hidden services
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Differences / limitations
We're TCP-only, not all IP (but we're user-space and very portable)
Not peer-to-peer
No protocol normalization
%%Not unobservable
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We have working code
Plus a design document,
and a byte-level specification
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http://freehaven.net/tor/
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