Web Filtering

Table of Contents Need of Filtering Content Filtering Basic Model Filtering Techniques Email Filtering Circumvent Filtering Problems with Filtering Conclusion

Review About Web Filter

Content Filtering

Analysis of Email and Web content Prevent malware and spam from

entering the network

Determine whether incoming data is harmful to the network or outgoing data includes intellectual property

Such data is then blocked from entering or leaving the network

Simple network layout

Network with traffic proxy

Web Security and Anti-Virus

Network Layout

Connection is made by forwarding the uninspected traffic straight to the destination.

Network with Traffic Proxied Traffic is received by an application which alters the traffic

in both the directions before sending to the destination.

Web Filtering Techniques Firewalls

URL Based Filtering

Content Analysis

Firewalls

Basic level of web filtering

Inspects traffic to identify requested site to make decision (allow or block)

Black Lists: Undesirable Web addresses

White Lists: Desirable Web addresses

URL Based Filtering Database of web addresses

Database loaded onto proxy servers, firewalls and other network infrastructure devices

Supports granular blocking

Content Analysis

Keyword Scanning

Image Scanning

Keywords Scanning Tag words: Positive or Negative

score

Block: Sum (score) > Threshold

Image Scanning

Content Analysis

Email Filtering Primary communication

channel

Need to control SPAM and virus mails

Filtering Techniques Channel/Response: Sender perform task

Heuristic Filters: Score words or phrases

Bayesian Filters: Mathematical Probability

Circumventing Web Filtering Getting around them: Traffic is not passed through the filter.

Getting through them: Traffic is passed through the filter by obscuring

the address of content and/or the content itself.

Type of Content Tested Accuracy Percentage

Content of an Adult Nature – direct URL access 87%

Content of an Adult Nature – keyword searches 81%

Content not of an Adult Nature – direct URL access 86%

Content not of an Adult Nature – keyword searches 69%

Image Searches 44%

Email Attachments 25%

RSS Feeds 48%

Catalog Searches 75%

Database Searches 88%

Internet Filtering Test

Problem with filtering "It could be expected that allowed

content would be blocked. If all pornographic content is to be blocked, other content with a resemblance in features will also be blocked; e.g. Adult education, medical information, erotic content etc."

“All filters over block. All filters under block. No filter is 100% accurate because no

one agrees on what being 100% accurate is.”

Conclusion

1.DansGuardian (Cross Platform, Free)2.K9 (Windows/Mac, Free)3.OpenDNS (Cross Platform, Free)4.SquidGuard/Squid (Linux, Free)5.Hosts File (Cross Platform, Free)

Five Best Content Filtering Tools

Use Of DansGuardian

Reference

1) http://dansguardian.org/?page=whatisdg2) http://www1.k9webprotection.com/aboutk9/overview3) https://www.opendns.com/about/4) https://www.opendns.com/about/5) http://en.wikipedia.org/wiki/Hosts_%28file%296) http://en.wikipedia.org/wiki/Internet_security