29-03-2011, 01:38 AM
I WANT project report of this topic(CAPTCHA in vb. net)
29-03-2011, 01:38 AM
I WANT project report of this topic(CAPTCHA in vb. net)
22-04-2011, 09:50 PM
Hi,
visit these threads for reports and ppt on captcha: https://seminarproject.net/Thread-c-...-humans-ap https://seminarproject.net/Thread-ca...9#pid29279 http://project-seminars.com/attachment.php?aid=8574
03-07-2013, 04:40 PM
CAPTCHA CAPTCHA.doc (Size: 484 KB / Downloads: 14) ABSTRACT One common application of CAPTCHA is for verifying online polls. In fact, a former Slashdot poll serves as an example of what can go wrong if pollsters don't implement filters on their surveys. In 1999, Slashdot published a poll that asked visitors to choose the graduate school that had the best program in computer science. Students from two universities -- Carnegie Mellon and MIT -- created automated programs called bots to vote repeatedly for their respective schools. While those two schools received thousands of votes, the other schools only had a few hundred each. If it's possible to create a program that can vote in a poll, how can we trust online poll results at all? A CAPTCHA form can help prevent programmers from taking advantage of the polling system. INTRODUCTION what is captcha? If you try to get a new email account at Yahoo, you'll be asked to prove that you're a human and not a computer. Why? Because a single computer program can get thousands of free email accounts per second. And that's bad for Yahoo. But how do you prove to a computer that you'rea human? Proving that you're a human to another human can be done using an idea from the 1950s: theTuring Test. A human judge asks you a bunch of questions and decides, depending on your answers, whether he's talking to a human or a computer. Proving that you're a human to a computer is another matter. It requires a test (or a set of tests) that computers can grade, humans can pass, but paradoxically, computers can't pass. In our lingo, it requires a captcha.so Why they are used CAPTCHAs are used to prevent robots from submitting forms and creating accounts, spamming and various other things. In some cases robots can cause some problems. Take for example a robot signing up for thousands of Gmail accounts. While it might not cause much stress on Gmail’s servers it would create lots of email accounts that could be used for spamming people. Another case is spammers creating accounts on forums and then spam the forum. CAPTCHAs help prevent robots from using websites and webapps. Insecure implementation Like any security system, design flaws in a system implementation can prevent the theoretical security from being realized. Many CAPTCHA implementations, especially those which have not been designed and reviewed by experts in the fields of security, are prone to common attacks. Some CAPTCHA protection systems can be bypassed without using OCR simply by re-using the session ID of a known CAPTCHA image. A correctly designed CAPTCHA does not allow multiple solution attempts at one CAPTCHA. This prevents the reuse of a correct CAPTCHA solution or making a second guess after an incorrect OCR attempt.[Other CAPTCHA implementations use a hash (such as an MD5 hash) of the solution as a key passed to the client to validate the CAPTCHA. Often the CAPTCHA is of small enough size that this hash could be cracked. Further, the hash could assist an OCR based attempt. A more secure scheme would use an HMAC . Finally, some implementations use only a small fixed pool of CAPTCHA images. Eventually, when enough CAPTCHA image solutions have been collected by an attacker over a period of time, the CAPTCHA can be broken by simply looking up solutions in a table, based on a hash of the challenge image. Computer character recognition A number of research projects have attempted (often with success) to beat visual CAPTCHAs by creating programs that contain the following functionality: 1. Pre-processing: Removal of background clutter and noise. 2. Segmentation: Splitting the image into regions which each contain a single character. 3. Classification: Identifying the character in each region. Steps 1 and 3 are easy tasks for computers. The only step where humans still outperform computers is segmentation. If the background clutter consists of shapes similar to letter shapes, and the letters are connected by this clutter, the segmentation becomes nearly impossible with current software. Hence, an effective CAPTCHA should focus on the segmentation. Several research projects have broken real world CAPTCHAs, including one of Yahoo's early CAPTCHAs called "EZ-Gimpy" and the CAPTCHA used by popular sites such as PayPal,[9] LiveJournal, phpBB, and other services. In January 2008 Network Security Research released their program for automated Yahoo! CAPTCHA recognition. Windows Live Hotmail and Gmail, the other two major free email providers, were cracked shortly after. In February 2008 it was reported that spammers had achieved a success rate of 30% to 35%, using a bot, in responding to CAPTCHAs for Microsoft's Live Mail service[ and a success rate of 20% against Google's Gmail CAPTCHA. A Newcastle University research team has defeated the segmentation part of Microsoft's CAPTCHA with a 90% success rate, and claim that this could lead to a complete crack with a greater than 60% rate. |
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