Overview of PHP development verification code tutorial

1. What is a verification code?

Verification code (CAPTCHA) is the abbreviation of "Completely Automated Public Turing test to tell Computers and Humans Apart" (fully automated Turing test to distinguish computers and humans). A public, fully automated program that distinguishes whether the user is a computer or a human. It can prevent: malicious cracking of passwords, ticket fraud, forum flooding, and effectively prevents a hacker from making continuous login attempts on a specific registered user using a specific program to violently crack the user. In fact, using verification codes is a common method for many websites now. We use This function is implemented in a relatively simple way. This question can be generated and judged by a computer, but only a human can answer it. Since computers cannot answer CAPTCHA questions, the user who answers the questions can be considered a human.

2 Introduction to verification code:

The word verification code was first coined in 2002 by Louis von Ahn and Manuel of Carnegie Mellon University. Proposed by Blum, Nicholas J. Hopper, and John Langford of IBM. Carnegie Mellon University tried to apply for the word to be a registered trademark. However, the application was rejected on April 21, 2008. A commonly used CAPTCHA test is to ask the user to input text or numbers displayed on a distorted picture. The distortion is to avoid being automatically recognized by computer programs such as optical character recognition (OCR, Optical Character Recognition). Alphanumeric digits lose their effect. Because this test involves computers testing humans, rather than humans testing computers as in the standard Turing test, people sometimes call CAPTCHA a reverse Turing test.

For people with disabilities who cannot see images, the alternative method is to use voice to read out the alphanumeric numbers. In order to prevent voice recognition from analyzing the voice, the content of the voice will be noisy.

3 Function

Prevent malicious cracking of passwords, ticket brushing, forum flooding, and page brushing.

Effectively prevent a hacker from using a specific program to brute force a specific registered user

to make continuous login attempts. In fact, using verification codes is a common method for many websites now (such as investment promotion) Bank's online personal banking, Baidu community), we have implemented this function in a relatively simple way. Although logging in is a little more troublesome, this function is still necessary and important for the password security of netizens. but we still We remind everyone to protect their passwords. Try to use a password of more than 6 characters mixed with numbers, letters, and symbols. Do not use simple passwords such as 1234 or passwords that are the same or similar to your username. , to prevent your account from being stolen and causing unnecessary trouble to you.

The verification code is usually composed of some lines and some irregular characters. Its main function is to prevent some hackers from digitizing the password and stealing it.

Four Usage Process

The verification code of most websites requires a click to fill in the box, and then the verification code image will automatically pop up.

Since the verification code is randomly generated, there is a high probability that there will be a verification code picture that cannot be clearly identified, so it should be noted that most websites will have corresponding prompts, such as "Can't see clearly, change another one", etc. , if there is no prompt, click directly on the current verification code image to complete the verification code replacement