题目链接:http://ctf5.shiyanbar.com/web/web200.jpg
加密
function encode ($str){
$_o = strrev($str); // 反转字符串
for ($_0=0;$_O<strlen($_o);$_O++); { // 所有字符ASCII值+1
$_c = substr($_o,$_O, 1);
$__ = ord($_c)+1;
$_c = chr($__);
$_ = $_.$c;
}
return str_rot13 (strrev(base64_encode ($_))) // 最终加密
}
解密
<?php
$str = "a1zLbgQsCESEIqRLwuQAyMwLyq2L5VwBxqGA3RQAyumZ0tmMvSGM2ZwB4tws";
$_ = "";
$_o = base64_decode(strrev(str_rot13($str))); // 初步解密
for ($_0=0;$_0<strlen($_O);$_O++) // 所有字符ASCII值-1
{
$_c = substr($_o,$_O,1);
$__ = ord($_c)-1;
$_c = chr($__);
$_= $_.$_c;
}
echo strrev($_); // 反转字符串
?>
得到flag:flag:{NSCTF_b73d5adfb819c64603d7237fa0d52977}