PHP AES-256-CBC 加密解密完整類別實作 (相容 Java)

加密需求背景

專案需與 Java 端對接，雙方約定使用 AES-256-CBC 模式、PKCS7 填充、固定 IV 向量。本文提供完整 PHP 類別實作，確保跨語言加解密互通。

核心加密類別

<?php 
class MCrypt {
    private $hex_iv = '00000000000000000000000000000000'; // 16 bytes IV
    private $key = 'U1MjU1M0FDOUZ.Qz'; // 原始金鑰
    
    function __construct() {
        // SHA-256 派生 32 bytes 金鑰
        $this->key = hash('sha256', $this->key, true);
    }
    
    function encrypt($str) {
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        mcrypt_generic_init($td, $this->key, $this->hexToStr($this->hex_iv));
        
        $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
        $pad = $block - (strlen($str) % $block);
        $str .= str_repeat(chr($pad), $pad); // PKCS7 填充
        
        $encrypted = mcrypt_generic($td, $str);
        mcrypt_generic_deinit($td);
        mcrypt_module_close($td);
        return base64_encode($encrypted);
    }
    
    function decrypt($code) {
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        mcrypt_generic_init($td, $this->key, $this->hexToStr($this->hex_iv));
        
        $str = mdecrypt_generic($td, base64_decode($code));
        $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
        
        mcrypt_generic_deinit($td);
        mcrypt_module_close($td);
        return $this->strippadding($str);
    }
    
    private function strippadding($string) {
        $slast = ord(substr($string, -1));
        $slastc = chr($slast);
        $pcheck = substr($string, -$slast);
        if (preg_match("/$slastc{" . $slast . "}/", $string)) {
            return substr($string, 0, strlen($string) - $slast);
        }
        return false;
    }
    
    function hexToStr($hex) {
        $string = '';
        for ($i = 0; $i < strlen($hex) - 1; $i += 2) {
            $string .= chr(hexdec($hex[$i] . $hex[$i+1]));
        }
        return $string;
    }
}

// 測試範例
$encryption = new MCrypt();
echo $encryption->encrypt('123456') . "<br/>";
echo $encryption->decrypt('tpyxISJ83dqEs3uw8bN/+w==');
?>

重要參數說明

⚠️ 遷移建議

PHP 7.1+ 已棄用 `mcrypt` 擴充套件，建議改用 `openssl_encrypt`/`openssl_decrypt` 實作相同邏輯，確保長期維護性。