Wednesday, November 21, 2007

CAPTCHA - Word verification

CAPTCHA is a type of challenge-response test used in computing to determine whether the user is human. "CAPTCHA" is a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart".

The following is a CAPTCHA.

There are two good articles about CAPTCHA on codinghorror.

The purpose of CAPTCHA is to make sure that, a human can do it very fast, but an automated script/program cannot do that.

If you take a normal programmer, who does not spend money on buying very expensive softwares, then breaking even the following code is also non-trivial, but it is very easily readable by humans.

If you have so much money (more than $6000), then you can break even the following code with 50% chance.

For this purpose, yahoo, gmail, and Hotmail came up with even more difficult CAPTCHAs. Sometimes, these are difficult even for humans. If the CAPTCHA is difficult for human, then the basic purpose is violated (i.e., not allowing a human to visit their website).

I like rapidshare approach very much. When you see the CAPTCHA image that they mention in rapidshare, it is very easy to understand. You don't need to spend any time to read the text in that. And, all the images, and characters in all the images are exactly of same structure and size. So, it tempts so-called programmers to write a script which cracks that. But, writing the program is not as simple as one can think of. Because, they use all the techniques of images while creating an image. There are few places in the image which one thinks as white, but actually it is black, and vice-versa. Because of these things, it would be very difficult to write a program. Even if someone writes, by the time, they finish it, rapidshare will change the image to another format like changing the size, and adding different shades etc. Again you will come back to square one. At the end of the day, you may need $6000 software to crack it. But, their CAPTCHA does not give any problem to the users. Where as other CAPTCHAs gives so many problems to the users.

There is another type of CAPTCHA in some other website.

Add 1 to 2 and type the result in the below text box.

For human, it hardly takes any time to find the result. Where as for computer, it is not trivial. If we make it even more complex, then it becomes even more difficult for computer. For example,

add 1234534512 to 1232429530.2322, and multiply the result with 12143298.4345 and divide it by 983435.234, and ignore this value, and put 4 in the below text box.

Something like above will be very easy for a normal user who can understand english properly, but, cannot be cracked by a computer in the next few years.

This is one area in which google is not meeting my expectations. understanding CAPTCHA of google is taking few seconds. I hope google will make it very easy for humans soon.

Tuesday, November 20, 2007

Google Maps and Google Earth

I have been using google maps for quite a long time. I thought google earth is also similar, but it is a desktop application. Today only I realized that, google maps cannot be compared with google earth. With google maps, we can get info upto main roads. Where as in google earth, we can see even our houses. I missed a lot, because of not knowing this earlier. Why is not google providing the same on their web version?

Tuesday, November 06, 2007

Useless Experiments by Government

In New Delhi, platform tickets will not be sold in railway station from Nov 7th to Nov 15th. Government says that, it is to reduce the rush in the railway station. Railways is selling around 65,000 platform tickets per day at the railway station, and if they don't sell, then there will be less rush in the railway station. Railways claim that, special permission can be granted for special cases.

I feel it is just another useless experiment by the government. It creates so many problems for senior citizens, and women with kids. I don't think taking special permission would be that much easy for an ordinary person. If an ordinary person wants to go inside railway station, first he/she needs to know that, they grant special permission for few people. They needs to know whom should they approach for that. Then, they have to find out the criteria for the special permission, and the list goes on. In that one week, Railways is going to lose 13.65 lakh rupees, because of this experiment.

Of course, for everything, there would be a work around. Just take a train ticket to next railway station, and you can go inside without having any platform ticket. If there is another railway station near by this railway station, then most of the time, you can get a ticket for less than Rs.5. It is better than platform ticket, because, we can stay whole day in the railway station, where as with platform ticket, we can stay only for 2 hours.

Friday, November 02, 2007

Stock Market

Once upon a time in a village, a man appeared and announced to the villagers that he would buy monkeys for Rs. 10/-

The villagers seeing that there were many monkeys around, went out to the forest and started catching them.

The man bought thousands at Rs. 10/- and as supply started to diminish, the villagers stopped their effort. He further announced that he would now buy at Rs. 20/- This renewed the efforts of the villagers and they started catching monkeys again.

Soon the supply diminished even further and people started going back to their farms. The offer rate increased to Rs. 25/- and the supply of monkeys became so little that it was an effort to even see a monkey, let alone catch it!

The man now announced that he would buy monkeys at Rs50! However, since he had to go to the city on some business, his assistant would now buy on behalf of him.

In the absence of the man, the assistant told the villagers. Look at all these monkeys in the big cage that the man has collected. I will sell them to you at Rs.35 and when the man returns from the city, you can sell it to him for Rs. 50/-

The villagers squeezed up with all their savings and bought all the monkeys.

Then they never saw the man nor his assistant, only monkeys everywhere!!!

Welcome to the 'Stock' Market!!!!!