quiz2-tor.md

Tor

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Resources

• Paper
• Blog posts: 1, 2, 3
• Lecture note from 2012
• Old quizzes

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Overview

• Goals
• Mechanisms
  • Streams/Circuits
  • Rendezvous Points & Hidden services
• Directory Servers
• Attacks & Defenses
• Practice Problems

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Goals

• Anonymous communication
• Responder anonymity
  • If I run a service like "mylittleponey.com" I don't want anyone associating me with that service
• Deployability / usability
  • Why a security goal?
    • Because it increases the # of people using Tor, i.e. the anonimity set
      • ...which in turn increases security
        • (adversary has more people to distinguish you amongst)
• TCP layer (Why? See explanations in lecture notes above)
• NOT P2P (because more vulnerable?)

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Circuit creation

TODO: Define circuit

Alice multiplexes many TCP streams onto a few circuits. Why? Low-latency system, expensive to make new circuit.

TODO: Define Onion Router (OR)

Directory server: State of network, OR public keys, OR IPs

ORs:

• All connected to one another with TLS
• See blog post 1: Authorities vote on consensus directory document

Example:

[ Draw example of Alice building a new circuit ]
[ and connecting to Twitter.                   ]

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Rendezvous Points & Hidden services

Example:

[ Add an example of Alice connecting to Bob's  ]
[ hidden service on Tor                        ]

Bob runs hidden service (HS):

• Decides on long term PK/SK pair
• Publish introduction points, advertises on lookup service
• Builds a circuit to Intro Points, waits for messages

Alice wants to connect to Bob's HS:

• Build circuit to new Rendezvous Point (RP) (any OR)
  • Gives cookie to RP
• Builds circuit to one of Bob's intro points and sends message
  • with {RP, Cookie, g^x}_PK(Bob)
• Bob builds circuit to RP, sends { cookie, g^y, H(K)}
• RP connects Alice and Bob