Monday, July 05, 2004
Gotcha ...... Captcha ?
The other day I was at my uncles place and he wanted to create a new email account on hotmail. I thought that I will help him out :)
Most of the procedure required to create a new email account was not new to me (just created my gmail account some time back). However, there was an interesting new element on the account creation form. There was this image displaying some text on it and below it there was a text box asking me to type in the text rendered above.
Now, that got me thinking....if the program which generated the form knows the text in the image then why does it want me to type it out again. For a moment I thought it was something new to do with encrypting stuff :)
I could not figure it out and simply typed in the text and completed the process of creating a new email account. Just last week I came across the following article on 'How to Spoof-proof your logins'
Eureka! Now I get it.....its captcha in action. The basic idea is to differentiate between humans and machines/programs. For example the text in the image on the (gimpy) page is very easy for us humans to comprehend. However, it is much difficult for a program to interpret.
Captcha is a typically employed technique to differentiate humans and programs apart. Captcha stands for "Completely Automated Public Turing Test to Tell Computers and Humans Apart". It has been widely used by Yahoo, Hotmail etc. Note captcha is not simply about a distorted image; it is any test, which most humans can pass but that current computer programs cannot. Captcha can be in various forms: Visual, audio etc.
Reference links (I am yet to read the last two, but they looked interesting enough to list here):
- How to Spoof-proof your logins
- Captcha project - Carnegie Mellon (School of computer science)
- Breaking a Visual Captcha
Most of the procedure required to create a new email account was not new to me (just created my gmail account some time back). However, there was an interesting new element on the account creation form. There was this image displaying some text on it and below it there was a text box asking me to type in the text rendered above.
Now, that got me thinking....if the program which generated the form knows the text in the image then why does it want me to type it out again. For a moment I thought it was something new to do with encrypting stuff :)
I could not figure it out and simply typed in the text and completed the process of creating a new email account. Just last week I came across the following article on 'How to Spoof-proof your logins'
Eureka! Now I get it.....its captcha in action. The basic idea is to differentiate between humans and machines/programs. For example the text in the image on the (gimpy) page is very easy for us humans to comprehend. However, it is much difficult for a program to interpret.
Captcha is a typically employed technique to differentiate humans and programs apart. Captcha stands for "Completely Automated Public Turing Test to Tell Computers and Humans Apart". It has been widely used by Yahoo, Hotmail etc. Note captcha is not simply about a distorted image; it is any test, which most humans can pass but that current computer programs cannot. Captcha can be in various forms: Visual, audio etc.
Reference links (I am yet to read the last two, but they looked interesting enough to list here):
- How to Spoof-proof your logins
- Captcha project - Carnegie Mellon (School of computer science)
- Breaking a Visual Captcha
Labels: Captcha
# posted by Paresh Borkar @ 11:14 AM 
