攻防世界高手进阶——web2

<?php 
$miwen="a1zLbgQsCESEIqRLwuQAyMwLyq2L5VwBxqGA3RQAyumZ0tmMvSGM2ZwB4tws"; 

function encode($str){ 
    $_o=strrev($str); 
    // echo $_o; 
         
    for($_0=0;$_0<strlen($_o);$_0++){ 
        
        $_c=substr($_o,$_0,1); 
        $__=ord($_c)+1; 
        $_c=chr($__); 
        $_=$_.$_c;    
    }  
    return str_rot13(strrev(base64_encode($_))); 
} 

highlight_file(__FILE__); 
/* 
   逆向加密算法，解密$miwen就是flag 
*/ 

题目提示逆向加密算法，所以只要把代码写出：

<?php
$str = "a1zLbgQsCESEIqRLwuQAyMwLyq2L5VwBxqGA3RQAyumZ0tmMvSGM2ZwB4tws";
$str = str_rot13($str);
$str = strrev($str);
$str = base64_decode($str);
$result = '';
for ($i = 0;$i < strlen($str);$i++){
    $temp = substr($str,$i,1);
    $get = ord($temp) - 1;
    $temp = chr($get);
    $result = $result . $temp;
}
$result = strrev($result);
echo $result;
?>

在线php执行：

flag:{NSCTF_b73d5adfb819c64603d7237fa0d52977}