CENSORSHIP RESISTANCE CMSC 414 APR 17 2018 CENSORSHIP COMES IN - - PowerPoint PPT Presentation

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CENSORSHIP RESISTANCE CMSC 414 APR 17 2018 CENSORSHIP COMES IN - - PowerPoint PPT Presentation

Mar 25, 2023 196 likes •657 views

CENSORSHIP RESISTANCE CMSC 414 APR 17 2018 CENSORSHIP COMES IN MANY FORMS DROPPING PACKETS Network operators : Block traffic in their own networks/countries Off-path attackers : Inject TCP RST packets (next week) Routing-capable adversaries

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SLIDE 1

CENSORSHIP
 RESISTANCE

CMSC 414

APR 17 2018

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SLIDE 2

CENSORSHIP COMES IN MANY FORMS

DROPPING PACKETS

Network operators: Block traffic in their own networks/countries Routing-capable adversaries: Can influence routes on the Internet Black-holing: Announce a low-cost path, drop traffic

MONITORING TRAFFIC MISDIRECTING TRAFFIC

DNS injection: Send back false DNS responses Boomerang routing: Source/destination close, but route goes through
 a country known to eavesdrop https://www.youtube.com/watch?v=IzLPKuAOe50

DEANONYMIZATION

Identifying and going after whistleblowers Off-path attackers: Inject TCP RST packets (next week)

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SLIDE 3

ENEMIES OF THE INTERNET

~Annual report by
 Reporters without Borders

2014

  • Syria
  • Russia
  • Saudia Arabia
  • UAE
  • Cuba
  • Belarus
  • Pakistan
  • Vietnam
  • Turkmenistan
  • Sudan
  • Iran
  • Bahrain
  • USA
  • UK
  • Uzbekistan
  • India
  • China
  • North Korea
  • Ethiopia
  • Surveillance


dealers

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SLIDE 4

ENEMIES OF THE INTERNET

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SLIDE 5

ENEMIES OF THE INTERNET

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SLIDE 6

ENEMIES OF THE INTERNET

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SLIDE 7

COLLATERAL DAMAGE OF INTERNET CENSORSHIP

China censors the traffic to or from
 those within its borders Known They do this via DNS injection Known / expected They do this to any traffic that
 traverses its borders Not known More traffic traverses China’s borders
 than we realized Oh geez..

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SLIDE 8

CIRCUMVENTING THE CONSTITUTION

Patriot Act
 Foreign Intelligence Surveillance Act (FISA)
 EO 12333

LEGAL REGIMES

Communication with foreign entities

WHAT CAN BE MONITORED?

What if the US routed traffic out of its
 borders, then back in — would this count
 as communication with a foreign entity?

DO ROUTERS COUNT? THIS PAPER: YES, PROBABLY

So any traffic could be easily monitored

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SLIDE 9

BLOCKING TOR

Downturn event: Drops below
 Possibly indicates censorship Estimate the number of users on
 day i based on previous days’ users Gray area: Range of estimated users;
 Usage naturally fluctuates Upturn event: Rises above “normal”
 Possibly indicates circumvention

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SLIDE 10

BLOCKING TOR

Downturn event: Drops below
 Possibly indicates censorship Estimate the number of users on
 day i based on previous days’ users Gray area: Range of estimated users;
 Usage naturally fluctuates Upturn event: Rises above “normal”
 Possibly indicates circumvention

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SLIDE 11

HOW TO BLOCK TOR

Option 1: Get a list of all Tor nodes
 Insert them as firewall rules Bridge nodes: Tor does not list some nodes;
 Users must learn them out of band Censors ca discover them by actively probing

Scan IP addresses, sending protocol-specific
 messages: handshake (TLS, obfs), Versions (Tor),
 HTTPS Post (SoftEther), HTTP GET (AppSpot)

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SLIDE 12

HOW TO BLOCK TOR

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SLIDE 13

HOW TO BLOCK TOR

Option 2: IP-based reputation schemes;
 Will eventually block exit nodes because
 attackers launder their attack traffic thru Tor

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SLIDE 14

DECOY ROUTING

Censoring regime Accepted website Censored website

𝗬

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SLIDE 15

DECOY ROUTING

Censoring regime Accepted website Censored website Decoy router, on the path
 to the accepted website

𝗬

After session initialization,
 divert traffic to the censored site How does the decoy router know the true destination but the censor doesn’t? Client includes “tags” in TLS handshakes that only the decoy router can identify

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SLIDE 16

DECOY ROUTING

Censoring regime Accepted website Censored website Decoy router, on the path
 to the accepted website

𝗬

After session initialization,
 divert traffic to the censored site How does the decoy router know the true destination but the censor doesn’t? Client includes “tags” in TLS handshakes that only the decoy router can identify

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SLIDE 17

DECOY ROUTING TAGS

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SLIDE 18

AVOIDING CENSORS

  • 1. Map the Internet
  • 2. Choose paths that do not go through the attackers’ countries

One approach

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SLIDE 19

AVOIDING CENSORS

  • 1. Map the Internet
  • 2. Choose paths that do not go through the attackers’ countries

Incredibly difficult research problem unto itself! One approach

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SLIDE 20

AVOIDING CENSORS

  • 1. Map the Internet
  • 2. Choose paths that do not go through the attackers’ countries

Incredibly difficult research problem unto itself! One approach Is it possible to get provable avoidance?

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SLIDE 21

SOME RESEARCH HERE AT UMD

Can we provably avoid countries
 known to censor/attack?

QUESTION DEMONSTRATES:

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SLIDE 22

SOME RESEARCH HERE AT UMD

Can we provably avoid countries
 known to censor/attack?

QUESTION

It is possible to get “provable
 avoidance” without even knowing
 where exactly packets go

DEMONSTRATES:

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SLIDE 23

Users lack control over routing

Mostly relegated to destination-based routing

send to

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SLIDE 24

Users lack control over routing

Mostly relegated to destination-based routing

send to

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SLIDE 25

Users lack control over routing

Collateral damage of censorship

send to

Censoring country Censor-free Censor-free

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SLIDE 26

Users lack control over routing

Collateral damage of censorship

✘

send to

Censoring country Censor-free Censor-free

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SLIDE 27

Users lack control over routing

Collateral damage of censorship

✘

send to

Censoring country Censor-free Censor-free

Encryption (HTTPS) Anonymity
 (Tor)

Hide info, but are still
 subject to censorship

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SLIDE 28

This work

✘

send to

Censoring country Censor-free Censor-free

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SLIDE 29

This work

send to

Censoring country Censor-free Censor-free

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SLIDE 30

Provable avoidance routing

send to but avoid

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SLIDE 31

Provable avoidance routing

send to but avoid

A broadly applicable primitive

Diffie-Hellman Provably disjoint paths Avoiding boomerangs Distinct vantage points

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SLIDE 32

Provable route avoidance goals

Provide proofs of avoidance

Proof

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

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SLIDE 33

Provable route avoidance goals

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

Provide proofs of avoidance

Proof

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SLIDE 34

Provable route avoidance goals

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

Without having to know
 underlying routes

Provide proofs of avoidance

Proof

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SLIDE 35

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

Provable route avoidance goals

Provide proofs of avoidance

Proof

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SLIDE 36

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

Provable route avoidance goals

Provide proofs of avoidance

Proof

Goal: proof that it did not traverse

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SLIDE 37

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

Provable route avoidance goals

Provide proofs of avoidance

Proof

Goal: proof that it did not traverse Non-goal: proof that it cannot traverse

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SLIDE 38

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

Provable route avoidance goals

Provide proofs of avoidance

Proof

Goal: proof that it did not traverse Non-goal: proof that it cannot traverse

Unadulterated roundtrip of communication

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SLIDE 39

Provable route avoidance goals

How do you prove that something did not happen? Provide proofs of avoidance

Proof

Users request their traffic to avoid
 transiting arbitrary geographic regions

Flexibility

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SLIDE 40

Proving the impossible

How do you prove did not happen
 without enumerating everything that could have? X

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SLIDE 41

Proving the impossible

How do you prove did not happen
 without enumerating everything that could have? X A

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SLIDE 42

Proving the impossible

How do you prove did not happen
 without enumerating everything that could have? X A A !X ⇒ &&

Mutually exclusive

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SLIDE 43

Proving the impossible

How do you prove did not happen
 without enumerating everything that could have? X A A !X ⇒ &&

Mutually exclusive

!X

⇒

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SLIDE 44

Proving the impossible

How do you prove did not happen
 without enumerating everything that could have? X A A !X ⇒ &&

Mutually exclusive

!X

⇒

A

is an alibi