XCTF-web2-JZTXT

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得到下方源码

 <?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
*/
?>

其中用到了一个没有见过的str_rot13()方法，了解后如下

![](https://img2023.cnblogs.com/blog/2442110/202311/2442110-20231127200209313-613231203.png)

奖该上述的代码反过来写一遍即可

<?php

$str = 'a1zLbgQsCESEIqRLwuQAyMwLyq2L5VwBxqGA3RQAyumZ0tmMvSGM2ZwB4tws';

$str = str_rot13($str);
$str = strrev($str);
$str = base64_decode($str);

for ($i=0; $i < strlen($str); $i++) { 
	$c = substr($str,$i,1);
	$ascii_c = ord($c)-1;
	$c = chr($ascii_c);
	$_str = $_str.$c;

}

$str = strrev($_str);
print($str);
?>