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1、 INTERNET CENSORSHIP The Information Blocking WallDi Wendw2464 Why Study Internet Censorship?Free SpeechInternet in Day-to-day Life Information SourceDifference from Other CensorshipsA Global Issue History of Internet CensorshipCensorship Has Been in Existence Almost as Long as Intellectual Explorat
2、ionThe History of Censorship Can be Traced Back to Ancient Times: Socrates, Protagras, Galileo, BulunuogaInternet Censorship Emerged in 1990s, Not Long After Usage of InternetCHINA: Great Fire Wall Started in 1998. Keeps Upgrading.USA: CDA (Communications Decency Act)COPA (Child On-line Protection A
3、ct) Internet Censorship Methods Non-technologicalTAKE-DOWN: Regulators Force Websites to Shut DownSELF-CENSORSHIP: Use Laws or Social Norms to Educate People Internet Censorship Methods Brute-forceFULL BLOCKCut off Routers. Disconnected from Worlds Internet.Used in 2011 Egyptian ProtestsSEARCH RESUL
4、T REMOVAL: Internet Search Service Company Cooperates with Government by Removing Forbidden Entries in Search ResultsStory of Baidu and Google in 2010Funny Words: River Crab, Grass Mud Horse, Six + Four Internet Censorship Methods Technical BlockingIP BLOCKINGBlock Access to Specific Hosting Servers
5、 with Banned IPOne of the Earliest StrategiesDNS TAMPERING Focus on Domain Names Instead of IP AddressesDNS Server Refuses to Resolve Domain Names, or Returns Wrong IP Addresses for the Domain NamesUsually Returns a Fake IP Which is Already Blocked “The Great DNS Wall of China” Comparison Between th
6、e Normal US DNS Servers and Tampered Chinese ServersRunning Two Rounds of DNS Query Tests Using the Same Set of Partially Tampered DomainsResult: Internet Censorship Methods Technical BlockingURL FILTERINGLook for Sensitive Strings in the URL Input into BrowserPACKET FILTERINGScan the Information Co
7、ntained in Packets, and Terminates the TCP Packet Transmissions When a Certain Number of Sensitive Keywords Are DetectedCONNECTION RESETSet 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 BlockedInternet
8、CensorshipBrute-forceNon-technologicalTechnical BlockingTake-down Self-censorshipFull BlockSearch Result RemovalIP BlockingDNS Tampering Internet Censorship MethodsURL FilteringPacket FilteringConnection Reset Analysis of Internet Censorship Methods Non-technological & Brute-ForceTAKE-DOWN & SELF-CE
9、NSORSHIPUseful in Countries Where Government Is Highly Centralized and Owns Great Power Over Its People DictatorshipNot Useful in Democratic Countries FULL BLOCK & SEARCH RESULT REMOVALSimple And Efficient No Way to Fight BackHigh Cost:Egyptians Lost $ 110 Million In the Internet Locking Jan 2011Chi
10、nese Government Received Unanimous Criticism for Google Quit Analysis of Internet Censorship Methods Technical BlockingAdvantage over Non-technical Blocking: There Are Websites Which Citizens Can Access But Government Has No ControlDisadvantage: Under-blocking & Over-blockingIP BLOCKING:Works for Al
11、l Protocols Based on IPDepends on the Accuracy of the Blacklist of Registered IPsIPs Keep Changing Difficult to Maintain AccuracyMay Falsely Block Accepted Websites on the Same Server of the Forbidden Websites on the ListEasily Bypassed Using Proxies Analysis of Internet Censorship Methods Technical
12、 BlockingDNS TAMPERING:Works for All Protocols Based on IPFocus on Domain Names Domain Names Seldom ChangeCircumvented by Looking for Not Tampered Foreign Servers Or Get IP Address via Other Ways besides DNS Queries InconvenientURL FILTERING:Only Works for HTTPAccuracy Depends on Blacklist of Blocke
13、d URL StringsBypassed by Escape Characters and VPNScunthorpe Problem: A String Is Blocked Because Its Text Contains a Substring of Letters Shared with Forbidden Strings Analysis of Internet Censorship Methods Technical BlockingPACKET FILTERING:Works for All Protocols Based on TCPFocus on TCP Packets
14、 Instead of Higher-level Input StringsScunthorpe ProblemCircumvented 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 packetCONNECTION RESETWorks for TCP-based ProtocolsAvoided by Omitting the Signal of Reset from Firewa
15、ll Analysis of Internet Censorship Methods SummaryDNS Tampering Looks to Be the Best SolutionBut The Choice Depends on Specific Situation Use as Much as Needed Future of Internet Censorship Techs Current Circumvention ToolsCame into Being Shortly after Censorship Technologies Cat-and -mouse GameWEB
16、PROXIESHides Connections between User and Forbidden ServerTUNNELING SOFTWAREA 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 DoesntPose Restriction on the Blocked Material in the Users Region Future o
