등록 브러시 공격을 효과적으로 방지하기 위해 PHP 확인 메커니즘을 사용하는 방법

<?php
session_start();
$width = 120;
$height = 40;
$image = imagecreatetruecolor($width, $height);
$bgColor = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $bgColor);
$fontFile = 'path/to/font.ttf';
$codeLength = 4;
$characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
$code = '';
for ($i = 0; $i < $codeLength; $i++) {
    $code .= $characters[rand(0, strlen($characters) - 1)];
}
$_SESSION['captcha_code'] = $code;
$textColor = imagecolorallocate($image, 0, 0, 0);
imagettftext($image, 20, 0, 10, 30, $textColor, $fontFile, $code);
header('Content-Type: image/png');
imagepng($image);
imagedestroy($image);

<?php
$ip = $_SERVER['REMOTE_ADDR'];
$timeLimit = 60; // 限制一分钟内同一个IP只能注册一次
$db = new PDO('mysql:host=localhost;dbname=test', 'username', 'password');
$stmt = $db->prepare('SELECT COUNT(*) FROM registrations WHERE ip=:ip AND created_at>:time');
$stmt->execute(array(':ip' => $ip, ':time' => time() - $timeLimit));
$count = $stmt->fetchColumn();
if ($count > 0) {
    // 同一个IP在限定时间内进行了多次注册，可以判断为刷注册攻击
    die('您的注册行为异常，请稍后再试。');
}

<?php
$limitInterval = 60; // 允许用户每隔60秒注册一次
$db = new PDO('mysql:host=localhost;dbname=test', 'username', 'password');
$stmt = $db->prepare('SELECT created_at FROM registrations WHERE email=:email ORDER BY id DESC LIMIT 1');
$stmt->execute(array(':email' => $email));
$lastRegistrationTime = $stmt->fetchColumn();
if ($lastRegistrationTime && $lastRegistrationTime > time() - $limitInterval) {
    // 在限定时间间隔内进行了多次注册，可以判断为刷注册攻击
    die('您的注册行为异常，请稍后再试。');
}