PHP verification code generation methods and solutions to common problems

With the continuous development of the Internet, people are paying more and more attention to data protection. Operations such as website login and registration need to be verified by verification codes to prevent malicious machine attacks and registration. Today I will share with you the PHP verification code generation method and solutions to common problems.

1. Verification code generation method

1. Use PHP GD library to generate image verification code

GD library is a graphics processing library in PHP that provides Many graphics operation functions. By using the GD library, we can quickly generate image verification codes.

The steps are as follows:

① Initialize the canvas: The imagecreatetruecolor() function can create a true color canvas according to the specified parameters. For example, imagecreatetruecolor(120, 40) creates a 120x40 pixel truecolor canvas.

② Draw interference background: Use the imagerectangle() function to draw some interference lines in a loop to make the verification code more difficult to be recognized by the machine.

③ Generate a random string: Generate a string of random strings as characters in the verification code image through random functions (rand() and mt_rand()).

④ Draw verification code characters to the canvas: Use the imagechar() function to draw a random string to the canvas.

⑤ Output the verification code image to the browser: use the header() function to set the Content-Type to image/png or image/jpeg, and use the imagepng() or imagejpeg() function to output the canvas to the browser for display .

The following is a simple PHP GD library verification code generation code:

<?php
session_start();
// 创建画布
$img = imagecreatetruecolor(120, 40);
//生成干扰线
for ($i = 0; $i < 5; $i++) {
    $color = imagecolorallocate($img, rand(0, 255), rand(0, 255), rand(0, 255));
    imageline($img, rand(0, 120), rand(0, 40), rand(0, 120), rand(0, 40), $color);
}
//生成随机验证码
$code = '';
for ($i = 0; $i < 4; $i++) {
    $code .= rand(0, 9);
}
//绘制验证码
$font = 'arial.ttf';
$text_color = imagecolorallocate($img, rand(0, 255), rand(0, 255), rand(0, 255));
imagettftext($img, 18, rand(-10, 10), 10, 24, $text_color, $font, $code);
//输出验证码图片到浏览器
header('Content-Type: image/png');
imagepng($img);
imagedestroy($img);
//将生成的验证码存储到Session中
$_SESSION['code'] = $code;
?>

2. Use the PHP GD library to generate a numeric verification code

The numeric verification code is mixed with respect to alphanumeric CAPTCHAs are simpler and easier to understand, so many websites use numeric CAPTCHAs. The following is a code example that uses the PHP GD library to generate a digital verification code:

<?php
session_start();
// 创建画布
$image = imagecreatetruecolor(120, 40);
// 生成干扰背景
$gray = imagecolorallocate($image, 200, 200, 200);
imagefill($image, 0, 0, $gray);
for ($i = 0; $i < 50; $i++) {
    $black = imagecolorallocate($image, 0, 0, 0);
    imagesetpixel($image, rand(0, 120), rand(0, 40), $black);
}
// 生成随机数字
$code = '';
for ($i = 0; $i < 4; $i++) {
    $code .= rand(0, 9);
}
// 将验证码写入画布中
$font = 'arial.ttf';
$white = imagecolorallocate($image, 255, 255, 255);
imagettftext($image, 20, 0, 15, 30, $white, $font, $code);
// 将验证码输出到浏览器
header('Content-Type: image/png');
imagepng($image);
imagedestroy($image);
// 存储验证码到Session中
$_SESSION['code'] = $code;
?>

3. Use a third-party library to generate a verification code

Although the PHP GD library just mentioned is powerful, there are some Disadvantages, such as the generated verification code image being too simple and easily cracked by robots. Therefore, we can use some third-party libraries to generate more complex verification codes.

For example, Gregwar/Captcha is a popular third-party verification code library that can generate various styles of verification code images. The method of use is also very simple. You only need to download the library and import the captcha.php file, and call the create() function to generate the verification code.

The following is a code example using the Gregwar/Captcha library to generate a verification code:

<?php
session_start();
require_once 'Captcha/autoload.php';
$captcha = new GregwarCaptchaCaptchaBuilder;
//配置验证码参数
$captcha->build(
    120,
    40,
    null, //font color
    true //background image
);

header('Content-Type: image/jpeg');
$captcha->output();
$code = $captcha->getPhrase();

$_SESSION['code'] = $code;
?>

2. Solutions to common problems

1. Insufficient complexity of the verification code pattern

As mentioned above, if the generated verification code pattern is too simple, it will be easily cracked by robots. In order to solve this problem, we can add various noise points, such as interference lines, arcs, background patterns, etc. The verification code generated in this way is more complex and improves security.

2. Generate multiple verification codes at the same time

Some robots will try to generate multiple verification codes in one second to crack the verification code. In order to prevent this attack, we can add some TimeDelay, that is, when the robot frequently submits verification codes, we can let it wait for a period of time before submitting again. This effectively prevents bot attacks.

3. The verification code expiration time is unclear

In actual projects, the verification code should not exist for too long, because as time goes by, the security of the verification code Sex will be reduced. We need to set the expiration time of the verification code (for example, 30 seconds) after generating the verification code, and verify it when submitting the verification code. If the expiration time is exceeded, the verification code must be regenerated.

Finally, we need to note that in actual applications, in addition to setting verification code protection, other forms of security protection measures are also required, such as SQL injection, XSS attacks and other solutions, in order to better protect Website security.

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