I NTERNET CENSORSHIP – The Information Blocking Wall Di Wen

1. INTERNET CENSORSHIP – The Information Blocking Wall Di Wen dw2464

2. Why Study Internet Censorship? • Free Speech • Internet in Day-to-day Life – Information Source • Difference from Other Censorships • A Global Issue

3. 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)

4. Internet Censorship Methods – Non-technological • TAKE-DOWN: Regulators Force Websites to Shut Down • SELF-CENSORSHIP: Use Laws or Social Norms to Educate People

5. 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

6. 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

7. “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:

8. 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

9. Internet Censorship Methods Take-down Non-technological Self-censorship Full Block Brute-force Search Result Removal Internet Censorship IP Blocking DNS Tampering Technical Blocking URL Filtering Packet Filtering Connection Reset

10. 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

11. 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

12. 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

13. 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 Packetngthe TCP/IP stack to reduce the amount of tein a packet • CONNECTION RESET • Works for TCP-based Protocols • Avoided by Omitting the Signal of Reset from Firewall

14. 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

15. 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

16. 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

17. 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……

18. THE END!