21-05-2012, 11:52 AM
CAPTCHA
CAPTCHA.docx (Size: 864.02 KB / Downloads: 49)
INTRODUCTION
A CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) is a program that generates and grades tests that are human solvable, but intends to be beyond the capabilities of current computer programs. It is a type of challenge-response test used in computing as an attempt to ensure that the response is generated by a person.
The process usually involves one computer (a server) asking a user to complete a simple test which the computer is able to generate and grade. Because other computers are supposedly unable to solve the CAPTCHA, any user enteri ng a correct solution is presumed to be human. Thus, it is sometimes described as a reverse Turing test, because it is administered by a machi ne and targeted to a human, in contrast to the standard Turing test that is typically administered by a human and targeted to a machine.
The most common use of CAPTCHA on the web today is to try preventi ng the repeatedly automatic submission of forms by bots, usually for the purpose of spam. By adding a CAPTCHA to form, it can cut down on the amount of spam received via a contact form or can prevent bots from signi ng up for accounts on the website.
TYPES OF CAPTCHA
The most common type of CAPTCHA involves the use of letters that are arranged randomly and are distorted in some way with various background colors. These types of CAPTCHAs can be seen when signing up for an e•mail account. There are various other types of CAPTCHAs and this classification is based on what is distorted and presented as a challenge to the user.
APPLICATIONS OF CAPTCHA
CAPTCHAs are used i n various Web applications to identify human users and to restrict access to them. CAPTCHA has several applications for practical security, which i ncludes the followi ng:
Prevent ing Comment Spam in Blogs:
There are various programs used by bloggers that submit bogus comments, usually for the purpose of raising search engi ne ranks of some website. This is called comment spam. B y usi ng a CAPTCHA, only humans ca n enter comments on a blog. There is no need to make users sign up before they enter a comment, and no
legitimate comments are ever lost. A CAPTCHA will not stop someone who is determined to post a rude message or harass an administrator, but it will help prevent bots from posti ng messages automatically.
CAPTCHA.docx (Size: 864.02 KB / Downloads: 49)
INTRODUCTION
A CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) is a program that generates and grades tests that are human solvable, but intends to be beyond the capabilities of current computer programs. It is a type of challenge-response test used in computing as an attempt to ensure that the response is generated by a person.
The process usually involves one computer (a server) asking a user to complete a simple test which the computer is able to generate and grade. Because other computers are supposedly unable to solve the CAPTCHA, any user enteri ng a correct solution is presumed to be human. Thus, it is sometimes described as a reverse Turing test, because it is administered by a machi ne and targeted to a human, in contrast to the standard Turing test that is typically administered by a human and targeted to a machine.
The most common use of CAPTCHA on the web today is to try preventi ng the repeatedly automatic submission of forms by bots, usually for the purpose of spam. By adding a CAPTCHA to form, it can cut down on the amount of spam received via a contact form or can prevent bots from signi ng up for accounts on the website.
TYPES OF CAPTCHA
The most common type of CAPTCHA involves the use of letters that are arranged randomly and are distorted in some way with various background colors. These types of CAPTCHAs can be seen when signing up for an e•mail account. There are various other types of CAPTCHAs and this classification is based on what is distorted and presented as a challenge to the user.
APPLICATIONS OF CAPTCHA
CAPTCHAs are used i n various Web applications to identify human users and to restrict access to them. CAPTCHA has several applications for practical security, which i ncludes the followi ng:
Prevent ing Comment Spam in Blogs:
There are various programs used by bloggers that submit bogus comments, usually for the purpose of raising search engi ne ranks of some website. This is called comment spam. B y usi ng a CAPTCHA, only humans ca n enter comments on a blog. There is no need to make users sign up before they enter a comment, and no
legitimate comments are ever lost. A CAPTCHA will not stop someone who is determined to post a rude message or harass an administrator, but it will help prevent bots from posti ng messages automatically.