Why anonymity?

• (Original) Motivation: protecting government communications
  • Journalist, activists &c

Why anonymity?

• (Original) Motivation: protecting government communications
  • Journalist, activists &c
• Threat models: traffic analysis (not content!)
  • Recipients via packet headers
  • Routes

Goals and non-goals

• Low-latency anonymity network
  • w/ deployability (for anonymity)
  • w/ usability (for anonymity)
  • w/ flexibility (protocol neutral)
• But, no end-to-end security

Two known approaches

• Mixnet
• Proxy

Tor: onion routing

• Overay network
• Onion Router
• Directory servers
• SOCKS proxy
• Crypto: DH/RSA, Circuit (fig1 in tor.pdf)

Directory servers

• Why do we need directory servers?
• How does it work?
• What if an adversary compromises a directory server?
• What if an adversary compromises N directory servers?
• What if directory servers are down?

Directory servers

  // @/src/or/config.c#l788
  static void
  add_default_trusted_dir_authorities(dirinfo_type_t type) {
    const char *authorities[] = {
      "moria1 orport=9101 no-v2 "
        "v3ident=D586D18309DED4CD6D57C18FDB97EFA96D330566 "
        "128.31.0.39:9131 9695 DFC3 5FFE B861 329B 9F1A B04C 4639 7020 CE31",
      "tor26 v1 orport=443"
        "v3ident=14C131DFC5C6F93646BE72FA1401C02A8DF2E8B4 "
        "86.59.21.38:80 847B 1F85 0344 D787 6491 A548 92F9 0493 4E4E B85D",
      ...
    };
  }

Hidden services

• Why do we want hidden services? (e.g., Wikileaks, The Pirate Bay)
• How does it work?
  • Introduction points
    • (e.g., Wikileaks: suw74isz7wqzpmgu.onion)
    • Service's public key
  • Rendezvous points
    • Relay the encrypted messages

Discussions

• What if an Introduction Point is compromised?
• What if a Rendezvous Point is compromised?

Demo

• status

   $ torsocks curl ifconfig.me
   $ torsocks w3m google.com
   $ arm check-speed

Safe (as user)?

• A student used tor for bomb threat (hoax)

Safe (as user)?

• Using tor actually helps FBI to catch the student?

Discussions

• Is it safe to access gmail?
• Is it safe to access http?
• Is it safe to run bittorrent?

Discussions

• What if an adversary compromises a single exit node?
• What if an adversary compromises N exit nodes?
• What if an adversary happens to compromise the entire OPs (N=3) in the circuit?
• What if an adversary happens to compromise the entire OPs, except one, in the circuit?
• What if an adversary compromises C out of N?
• Heartbleed bugs?