Concept Doppler: A weather Tracker For

Internet Censorship

Author: Jedidiah R. Crandall, Danial Zinn, Michael Byrd, Earl Barr, Rich East

Presented At: 14th ACM Conference on CCS , 29-Nov 2007

Prepared By: Amit Shrivastava

Understanding the relationship between sensitive concepts and blocked keywords will lead to more effective tracking of Internet censorship.

Motivation

Experiment

Great Firewall of China (GFC) is a system set up by the Chinese government for censoring the Internet.

Concept Doppler : An architecture to track the list of keywords that a government uses to censor Internet using GFC (Great firewall of china)

LSA (Latent Semantic analysis) an efficient way to produce a blacklist of censored words via probing.

Internet Censorship in China

Called the “Great Firewall of China,” or “Golden Shield” IP address blocking DNS redirection Legal restrictions etc… Keyword filtering

Blog servers, chat, HTTP traffic

Censorship of GET Requests

.

GET falun.html

RST RST

ConceptDoppler Framework

Discovering GFC Router

Locating Filtering Routers

.

TTL=2 falun

ICMP ErrorTTL=1 falunRST RST

First Hops

•ChinaNET performed 77% of all filtering, and 99.1% of all filtering at the first hop

Latent Semantic Analysis

.

LSA-Continuation

ni,j is the number of occurrences of the considered term in document dj,

the denominator is the number of occurrences of all terms in document dj.

| D | : total number of documents in the corpus   : number of documents where the term ti appears.

LSA-Continuation

.

the dot product between two term vectors gives the correlation between the terms over the documents. The matrix product XXT contains all these dot products.

the matrix XTX contains the dot products between all the document vectors, giving their correlation over the terms.

Result

They found 122 key words

Contribution

Paper Provided LSA which is an effective manner for understanding between sensitive concept and blocked keywords which led to more effective tracking of internet censorship.

Weekness

ConceptDoppler functionality not clearly explained.

Author has taken GFC for explaining conceptDoppler but its not certain weather his experiment will be effective in other network as well.

How to improve

Detailed information about functionality of ConceptDoppler.

Novel algorithm for LSA to get complete coverage of blacklist words.

.

Thank You