cse 592 internet censorship (fall 2015) lecture 19 phillipa gill - stony brook u

CSE 592INTERNET CENSORSHIP

(FALL 2015)

LECTURE 19

PHILLIPA GILL - STONY BROOK U.

WHERE WE ARE

Last time:

• Mitigating timing attacks (Astoria)

Today:

• Finish up mitigating timing attacks (LASTor)

• Other approaches to anonymity systems;

• Dissent• Aqua

Administravia:

• Mark update on Piazza.

THE DISSENT PROJECT

Goal: rethink the foundations of anonymity

Offer quantifiable and measurable anonymity

Build on primitives offering provable security

Don't just patch specific vulnerabilities, butrearchitect to address whole attack classes

http://dedis.cs.yale.edu/dissent/

Not a drop-in replacement for onion routing, but offers some systematic defense against all 5 classes of vulnerabilities

• ACKs: http://dedis.cs.yale.edu/dissent/pres/131024-austin.pdf




http://dedis.cs.yale.edu/dissent/pres/131024-austin.pdf

DINING CRYPTOGRAPHERS (DC-NETS)

• 3 cryptographers eating dinner and the waiter informs them that the meal has been paid by someone

• Cryptographers want to know if it was one of them or the NSA

• They respect each others right to make an anonymous payment …

• … but want to know if the NSA paid

• Solution: 2 stage protocol

1. Each pair of cryptographers exchanges a secret (e.g., flip a coin behind a menu)

2. Announce a bit; XOR of bits shared with neighbors (if they did not pay) or the opposite of this (if they did pay)

EXAMPLE OF DINING CRYPTOGRAPHERS

TOWARDS EFFICIENT TRAFFIC-ANALYSIS RESISTANT ANONYMITY NETWORKS

Stevens Le Blond David Choffnes Wenxuan ZhouPeter Druschel Hitesh Ballani Paul Francis

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Snowden wants to communicate with Greenwald without Alexander to find out

Ed’s IP Glenn’s IP

THE PROBLEM OF IP ANONYMITY

Client Server

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VPN proxy

Proxies are single point of attack(rogue admin, break in, legal, etc)

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Proxy

Traffic analysisOnion routing (Tor)

Onion routing doesn’t resisttraffic analysis (well known)

OUTLINE

1) Overview

2) Design

3) Evaluation

4) Ongoing work

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ANONYMOUS QUANTA (AQUA)

k-anonymity: Indistinguishable among k clients

BitTorrent

• Appropriate latency and bandwidth• Many concurrent and correlated flows

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Threat model

Global passive (traffic analysis) attack

Active attack

Edge mixes aren’t compromised

Padding

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Constant rate (strawman)

Defeats traffic analysis, but overhead proportionalto peak link payload rate on fully connected network

OUTLINE

1) Overview

2) Design

• Padding at the core• Padding at the edges• Bitwise unlinkability• Receiver’s anonymity (active attacks)

3) Evaluation

4) Ongoing work

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Multipath

Multipath reduces thepeak link payload rate

Padding

VARIABLE UNIFORM RATE

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Reduces overhead by adapting tochanges in aggregate payload traffic

OUTLINE

1) Overview

2) Design


3) Evaluation

4) Ongoing work

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K-ANONYMITY SETS (KSETS)

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Send ksetRecv kset

Provide k-anonymity by ensuring correlatedrate changes on at least k client links

Padding

FORMING EFFICIENT KSETS

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Epochs1 2 3

Peer

s’ ra

tes

1

2

3

Are there temporal and spatialcorrelations among BitTorrent flows?

OUTLINE

1) Overview

2) Design


3) Evaluation

4) Ongoing work

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METHODOLOGY: TRACE DRIVEN SIMULATIONS

Month-long BitTorrent trace with 100,000 users

• 20 million flow samples per day• 200 million traceroute measurements

Models of anonymity systems

• Constant-rate: Onion routing v2• Broadcast: P5, DC-Nets• P2P: Tarzan• Aqua

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OVERHEAD @ EDGES

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Models

Ove

rhea

d

Much better bandwidth efficiency

THROTTLING @ EDGES

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Models

Thro

ttlin

g

Efficiently leveragescorrelations in BitTorrent flows

OUTLINE

1) Overview

2) Design

2) Evaluation

3) Ongoing work

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ONGOING WORK

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Prototype implementation

Aqua for VoIP traffic

• “tiny-latency” (RTT <330ms)

Intersection attacks

Workload independence

TAKE HOME MESSAGESEfficient traffic-analysis resistance by exploiting existing correlations in BitTorrent traffic

At core:

• Multipath reduces peak payload rate

• Variable uniform rate adapts to changes in aggregate payload traffic

At edges, ksets:

• Provide k-anonymity by sync rate on k client links• Leverage temporal and spatial correlations of BitTorrent flows

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HANDS ON ACTIVITY

(Try at home )

Dissent source code is publicly available:

https://github.com/DeDiS/Dissent

Try downloading/installing/running the system

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cse 592 internet censorship (fall 2015) lecture 19 phillipa gill - stony brook u

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