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Anticensorship in the Network Infrastructure

Anticensorship in the Network Infrastructure. Eric Wustrow University of Michigan. Background | Internet Censorship. Pervasive censorship. Substantial censorship. Selective censorship. Changing situation. Little or no censorship. Threat Model.

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Anticensorship in the Network Infrastructure

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  1. Anticensorshipin the Network Infrastructure Eric Wustrow University of Michigan

  2. Background | Internet Censorship Pervasive censorship Substantial censorship Selective censorship Changing situation Little or no censorship

  3. Threat Model Censor … controls client’s network, but not external network … blocks according to a blacklist … allows HTTPS connections to non-blocked sites

  4. Telex | Overview

  5. Telex | Overview

  6. Telex | Overview

  7. Telex | Overview

  8. Telex | Overview

  9. Telex | Overview

  10. Prototype | Test Deployment Single Telex Station on lab-scale “ISP” at Michigan Hosted sites Blocked.telex.ccSimulated censored siteonly reachable via Telex NotBlocked.telex.ccUnobjectionable content* Inline Blocking Asymmetric flows

  11. Telex v2: Passive tap

  12. New architecture -- passive ISP tap Client ISP Proxy Server TLS Handshake Plaintext: “GET / HTTP/1.1\r\nX-Ignore: \x81\x28\x66 …” Ciphertext: “\x95\x1f\x6b\x27\xe2 … \xc8\x3f\x22 …” ACK [seq=Y, ack=X] “PROXY OK” [seq=Y, ack=X, len=M] Plaintext: ack != Y? ACK [seq=X, ack=Y+M] Plaintext: “GET http://blocked.com/ …” [seq=X, ack=Y+M] Tag: “HTTP/1.1 200 OK … <html> ….” Plaintext:

  13. New architecture -- passive ISP tap • Pros • No inline blocking required, only passive tap • Works with asymmetric flows (client -> server) • Cons • Censor can use active attacks • (though we can use “active defenses”)

  14. Anticensorship in the Network Infrastructure • Future work • Looking for ISPs willing to help • Technical feedback • Prototype deployment • Strategies for optimal deployment • Improving traffic analysis defense

  15. Anticensorshipin the Network Infrastructure https://telex.cc Eric Wustrow Colleen M. Swanson Scott Wolchok Ian Goldberg J. Alex Halderman

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