INTERNET

CENSORSHIP

– The Information

Blocking Wall

Di Wen dw2464

Why Study Internet Censorship?

Free Speech Internet in Day-to-day Life – Information Source Difference from Other Censorships A Global Issue

History of Internet Censorship

Censorship Has Been in Existence Almost as Long as Intellectual Exploration

The History of Censorship Can be Traced Back to Ancient Times: Socrates, Protagras, Galileo, Bulunuoga

Internet Censorship Emerged in 1990s, Not Long After Usage of Internet

CHINA: Great Fire Wall Started in 1998. Keeps Upgrading.

USA: CDA (Communications Decency Act) COPA (Child On-line Protection Act)

Internet Censorship Methods – Non-technological

TAKE-DOWN: Regulators Force Websites to Shut Down

SELF-CENSORSHIP: Use Laws or Social Norms to Educate People

Internet Censorship Methods – Brute-force

FULL BLOCK

Cut off Routers. Disconnected from World's Internet. Used in 2011 Egyptian Protests SEARCH RESULT REMOVAL:

Internet Search Service Company Cooperates with Government by Removing Forbidden Entries in Search Results

Story of Baidu and Google in 2010 Funny Words: River Crab, Grass Mud Horse, Six + Four

Internet Censorship Methods – Technical Blocking

IP BLOCKING

Block Access to Specific Hosting Servers with Banned IP One of the Earliest Strategies

DNS TAMPERING

Focus on Domain Names Instead of IP Addresses DNS Server Refuses to Resolve Domain Names, or Returns

Wrong IP Addresses for the Domain Names Usually Returns a Fake IP Which is Already Blocked

“The Great DNS Wall of China”

Comparison Between the Normal US DNS Servers and Tampered Chinese Servers

Running Two Rounds of DNS Query Tests Using the Same Set of Partially Tampered Domains

Result:

Internet Censorship Methods – Technical Blocking

URL FILTERING Look for Sensitive Strings in the URL Input into Browser

PACKET FILTERING Scan the Information Contained in Packets, and

Terminates the TCP Packet Transmissions When a Certain Number of Sensitive Keywords Are Detected

CONNECTION RESET Set the Firewalls So That the System Will Automatically

Block Connections from/to an Entity for a Period of Time if the Previous TCP Connection was Blocked

Internet Censorship

Brute-force

Non-technological

Technical Blocking

Take-down

Self-censorship

Full Block

Search Result Removal

IP Blocking

DNS Tampering

Internet Censorship Methods

URL Filtering

Packet FilteringConnection

Reset

Analysis of Internet Censorship Methods – Non-technological & Brute-Force

TAKE-DOWN & SELF-CENSORSHIP

Useful in Countries Where Government Is Highly Centralized and Owns Great Power Over Its People – Dictatorship

Not Useful in Democratic Countries

FULL BLOCK & SEARCH RESULT REMOVAL

Simple And Efficient – No Way to Fight Back High Cost: Egyptians Lost $ 110 Million In the Internet Locking Jan 2011 Chinese Government Received Unanimous Criticism for Google

Quit

Analysis of Internet Censorship Methods

– Technical Blocking

Advantage over Non-technical Blocking: There Are Websites Which Citizens Can Access But Government Has No Control

Disadvantage: Under-blocking & Over-blocking

IP BLOCKING:

Works for All Protocols Based on IP Depends on the Accuracy of the Blacklist of Registered IPs IPs Keep Changing – Difficult to Maintain Accuracy May Falsely Block Accepted Websites on the Same Server of

the Forbidden Websites on the List Easily Bypassed Using Proxies

Analysis of Internet Censorship Methods

– Technical Blocking

DNS TAMPERING: Works for All Protocols Based on IP Focus on Domain Names – Domain Names Seldom Change Circumvented by Looking for Not Tampered Foreign Servers

Or Get IP Address via Other Ways besides DNS Queries – Inconvenient

URL FILTERING: Only Works for HTTP Accuracy Depends on Blacklist of Blocked URL Strings Bypassed by Escape Characters and VPN Scunthorpe Problem: A String Is Blocked Because Its Text

Contains a Substring of Letters Shared with Forbidden Strings

Analysis of Internet Censorship Methods

– Technical Blocking

PACKET FILTERING:

Works for All Protocols Based on TCP Focus on TCP Packets Instead of Higher-level Input Strings Scunthorpe Problem Circumvented by VPN Or Modifying the TCP/IP Stack to

Reduce the Amount of Text in a Packetng the TCP/IP stack to reduce the amount of te in a packet

CONNECTION RESET

Works for TCP-based Protocols Avoided by Omitting the Signal of Reset from Firewall

Analysis of Internet Censorship Methods

– Summary

DNS Tampering Looks to Be the Best Solution But The Choice Depends on Specific Situation – Use as Much

as Needed

Future of Internet Censorship Techs – Current Circumvention Tools

Came into Being Shortly after Censorship Technologies – Cat-and-mouse Game

WEB PROXIES Hides Connections between User and Forbidden Server

TUNNELING SOFTWARE A Means for Communication from Network Locations with

Restricted Connectivity: behind NATs, Firewalls, etc.

VPNs (Virtual Private Networks) Build a Secure Connection to Another Region Which

Doesn't Pose Restriction on the Blocked Material in the User's

Region

Future of Internet Censorship Techs –Trends of Censorship Technologies

Move Filtering from Browsers to Web Proxies

Easier Maintenance and Better Compatibility No Longer Able to Bypass Internet Censorship by Any

Modifications or Deletions on Browsers

Move from Static Detection to Dynamic Analysis

Solve the Problem of Accuracy of Blacklist in IP & URL Blocking

Keyword-matching on Every Page Instead of Per Website Kills the Attempts to Fight against Censorship by Changing IP

Addresses or URL Strings

Conclusions

Non-Technical Methods are Powerful, but Have Limited Usage

Technical Blocking Methods Are Preferable. The Government Should Choose among the Technical Blocking Methods According to the Practical Conditions and Implement as Many Methods as Possible to Fight against Different Kinds of Anti-censorship Users

Future Trends: Combination of Proxy Servers and Dynamic Content Analysis Can Make Internet Censorship More Efficient and Powerful

The Cat-and-mouse Games Go Marching On……

THE END!