358 lines
8.2 KiB
Plaintext
358 lines
8.2 KiB
Plaintext
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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%nodefault
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%center, size 9, font "thick", back "white", fore "black"
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Tor:
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%size 8
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Next-generation Onion Routing
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%size 7
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Roger Dingledine
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Nick Mathewson
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Paul Syverson
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The Free Haven Project
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%font "typewriter", fore "blue"
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http://freehaven.net/
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Low-latency anonymity system
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%leftfill
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Deployed: 20 nodes, hundreds (?) of users
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Many improvements on earlier design
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Free software -- modified BSD license
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Design is not covered by earlier onion routing
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patent
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Uses SOCKS to interface with client apps
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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We have working code
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(14 kloc of C)
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and a design document,
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and a byte-level specification,
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and a Debian package (in Unstable)
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Works on Linux, BSD, OSX, Cygwin, ...
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User-space, doesn't need kernel mods or root
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%size 9
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http://freehaven.net/tor/
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%page
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%%
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%%Talk Overview
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%%
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%%A bit about Onion Routing
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%%
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%%Improvements we've made
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%%
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%%Some related work
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%%
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%%Ask me questions
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%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Anonymity: Who needs it?
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Private citizens
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advocacy, counseling, whistleblowing, reporting, ...
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%size 6
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Higher-level protocols
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voting, e-cash, auctions
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%size 6
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Government applications
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research, law enforcement
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%size 6
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Business applications
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%size 5
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(hide relationships and volumes of communication)
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Who is visiting job sites?
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Which groups are talking to patent lawyers?
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Who are your suppliers and customers?
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Is the CEO talking to a buyout partner?
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Anonymity is a network effect
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Systems need traffic (many low-sensitivity users) to attract the high-sensitivity users
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Most users do not value anonymity much
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Weak security (fast system) can mean more users
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which can mean
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%cont, font "italic"
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stronger
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%cont, font "standard"
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anonymity
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High-sensitivity agents have incentive to run nodes
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so they can be certain first node in their path is good
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to attract traffic for their messages
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There can be an optimal level of free-riding
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Onion Routing is...
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An overlay network
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Users build virtual circuits through the network
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One layer of encryption at each hop
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Fixed-size cells
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Tor's goals
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Conservative design
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minimize new design work needed
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%size 6
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Support testing of future research
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Design for deployment; deploy for use
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Threat model -- what we aim for
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Protect against somebody watching Alice
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Protect against curious Bob
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Protect against `some' curious nodes in the middle
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Differences / limitations
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We're TCP-only, not all IP (but we're user-space and very portable)
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Not as strong as high-latency systems (Mixmaster, Mixminion)
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Not peer-to-peer
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No protocol normalization
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Not unobservable (no steg, etc)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Perfect forward secrecy
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Telescoping circuit
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negotiates keys at each hop
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no more need for replay detection
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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No mixing, padding, traffic shaping (yet)
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Please show us they're worth the usability tradeoff
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%page
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%%
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%%Many TCP streams can share one circuit
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%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Many TCP streams share a circuit
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Previous designs built a new circuit for each stream
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lots of public key ops per request
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plus anonymity dangers from making so many circuits
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Leaky-pipe circuit topology
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Alice can direct cells to any node in her circuit
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So we can support long-range padding,
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have multiple streams exiting at different places in the circuit
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etc
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%size 6
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Unclear whether this is dangerous or useful
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More research needed
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Congestion control
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Simple rate limiting
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Plus have to keep internal nodes from overflowing
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(Can't use global state or inter-node control)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Directory servers
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To solve the `introduction' problem
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Approve new servers
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Tell clients who's up right now
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plus their keys, location, etc
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Variable exit policies
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Each server allows different outgoing connections
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E.g. no servers allow outgoing mail currently
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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End-to-end integrity checking
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In previous onion routing, an insider could change
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the text being transmitted:
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"dir" => "rm *"
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Even an external adversary could do this!
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Rendezvous points
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allow hidden services
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don't need (brittle) reply onions
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Access-controlled: Bob can control who he talks to
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Robust: Bob's service is available even when some Tor nodes go down
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Smear-resistant: Evil service can't frame a rendezvous router
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Application-transparent: Don't need to modify Bob's apache
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%size 6
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(Not implemented yet)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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How do we compare security?
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Assume adversary owns c of n nodes
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can choose which
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%size 6
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What's the chance for a random Alice and Bob that he wins?
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Freedom, Tor: (c/n)^2
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Peekabooty, six-four, etc: c/n
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Jap (if no padding): 1 if c>1
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Anonymizer: 1 if c>0
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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Future work
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Threshold directory agreement
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Scalability: Morphmix/p2p extensions?
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Restricted-route (non-clique topology)
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Non-TCP transport
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Implement rendezvous points
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Make it work better
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%page
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We have working code
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Plus a design document,
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and a byte-level specification
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and a Debian package (in Unstable)
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%size 9
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http://freehaven.net/tor/
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%size 6
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Privacy Enhancing Technologies workshop
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%size 9
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http://petworkshop.org/
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