WebBots
- 1. Fighting the WebBots • A webbot is a program that visits web sites for all kinds of purposes. • For example, Google webbots make copies of all web sites for their search engines. • The challenge is to stop malicious webbots 6/7/2011 ITS102-12, Third Class 1
- 2. Webbots and Spam • Spammers send webbots to get e-mail accounts from sites that offer them for free. • How can you tell that someone who asks for an e-mail account is a person or a webbot? 6/7/2011 ITS102-12, Third Class 2
- 3. Are you a person or a bot? • We know that there are certain things that computers cannot do. • Ask the “applicant” to do something that computers cannot do. • Cook a meal? • Read something impossible for computers to read! 6/7/2011 ITS102-12, Third Class 3
- 4. CAPTCHA • Completely Automated Public Turing test to tell Computers and Humans Apart 6/7/2011 ITS102-12, Third Class 4
- 5. CAPTCHA • CAPTCHA does not have to be text, but “computer unreadable” text is convenient. • Alternatives include pictures. • For example, ask if a person in a pictures is smiling or not. What is wrong with such a CAPTCHA 6/7/2011 ITS102-12, Third Class 5
- 6. How Computers Read Optical Character Recognition (OCR) • Step 1: Separate print (usually dark) from background (usually light). • Step 2: Pick up individual characters (group of dark pixels) • Step 3: Identify their shape by looking for strokes, loops, corners, etc • Step 4: Use rules to classify. For example, an H has two vertical strokes and a short horizontal strokes. 6/7/2011 ITS102-12, Third Class 6
- 7. Frustrating OCR Separate 1 background Use messy background. from print Pick up Have them blend with 2 individual characters each other. Find strokes, 3 loops, etc Make the letters “wiggly” Apply It should be hopeless by 4 classification rules this point. 6/7/2011 ITS102-12, Third Class 7
- 8. Make your own CAPTCHA • A web site that offers you the means: • www.codeproject.com/KB/aspnet/ CaptchaImage.aspx • For a general tutorial see: • www.theopavlidis.com/technology/ captcha/tutorial.htm 6/7/2011 ITS102-12, Third Class 8
- 9. Some Weak CAPTCHAs From Paypal From Yahoo’s Briefcase 6/7/2011 ITS102-12, Third Class 9
- 10. Some CAPTCHAs that may be too hard for people From Yahoo: From Passport: 6/7/2011 ITS102-12, Third Class 10
- 11. But Human Vision is Amazing 6/7/2011 ITS102-12, Third Class 11
- 12. But Human Vision is Amazing 6/7/2011 ITS102-12, Third Class 12
- 13. Non Text CAPTCHAs • Use pictures as CAPTCHAs • Plus: There are very tough to break • Minus: – Need to label a huge number of pictures. – If we use few pictures the webbot can just keep guessing. 6/7/2011 ITS102-12, Third Class 13
- 14. Synthetic Pictures (an idea by M. Kaplan) Please click on or enter each letter corresponding to the following list in the field below. You must enter them in the exact sequence listed. C K 6/7/2011 ITS102-12, Third Class 14