PHP data filtering: preventing connection timeouts and denial of service attacks

PHP Data Filtering: Preventing Connection Timeouts and Denial of Service Attacks

Introduction:
With the rapid development of the Internet, network security issues have become increasingly prominent. Connection timeouts and denial of service (DDoS) attacks are two important issues in the field of network security. This article will focus on how to use PHP data filtering to prevent connection timeouts and denial of service attacks, and provide specific code examples.

1. Connection timeout attack
Connection timeout attack means that the attacker occupies server resources by sending a large number of invalid requests, causing legitimate users to be unable to access the website normally. The following are some common PHP data filtering techniques that can help us prevent connection timeout attacks.

1. Verify data length:
   Before processing the data submitted by the user, we can use the strlen() function to verify whether the length of the data is legal. For example, we can perform length validation on the username submitted by the form as follows:

$username = $_POST['username'];
if(strlen($username) > 20) {
    echo "用户名长度不能超过20个字符。";
    exit;
}

2. Filter malicious characters:
   We can use regular expressions or string functions to filter Malicious characters in user input. The following is an example of using regular expressions to filter HTML tags:

$input = $_POST['input'];
$filtered_input = preg_replace('/<[^>]*>/', '', $input);

3. Limit request frequency:
   We can use session or IP address to limit the frequency of user requests. The following is a sample code that uses session to limit users to submit only once per minute:

session_start();
if(isset($_SESSION['last_request_time'])) {
    $time_diff = time() - $_SESSION['last_request_time'];
    if($time_diff < 60) {
        echo "您的请求频率过快，请稍后再试。";
        exit;
    }
}
$_SESSION['last_request_time'] = time();

2. Denial of Service (DDoS) Attack
Denial of Service (DDoS) attack is when an attacker passes Sending a large number of requests prevents the server from properly responding to requests from legitimate users. The following are some common PHP data filtering techniques that can help us prevent denial of service attacks.

1. Limit the number of concurrent connections:
   We can use the sem_acquire() and sem_release() functions to limit the number of concurrent connections. The following is a sample code that limits the number of concurrent connections to 100:

$sem_key = ftok(__FILE__, 'a');
$sem_id = sem_get($sem_key);
if(!sem_acquire($sem_id)) {
    echo "服务器繁忙，请稍后再试。";
    exit;
}
// 处理请求
sem_release($sem_id);

2. Use verification code:
   We can use the verification code to confirm the user's identity before the user submits important operations. The following is a sample code that uses the GD library to generate a verification code:

session_start();
$code = '';
for($i = 0; $i < 4; $i++) {
    $code .= chr(rand(65, 90));
}
$_SESSION['captcha'] = $code;
$im = imagecreatetruecolor(100, 30);
$bg_color = imagecolorallocate($im, 255, 255, 255);
$text_color = imagecolorallocate($im, 0, 0, 0);
imagefill($im, 0, 0, $bg_color);
imagestring($im, 5, 10, 8, $code, $text_color);
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);

Conclusion:
By performing reasonable filtering on user-submitted data, we can effectively prevent connection timeouts and denial of service ( DDoS) attack. This article provides some common PHP data filtering techniques and gives corresponding code examples. I hope it will be helpful to readers when writing secure PHP code. Remember, network security is an important issue, and we should always pay attention and take appropriate measures to protect our systems and users' private information.

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