整理的discuz中php字串加密解密函数

<?php
 
//加解密函数

//加密
//$encode = authcode('我要加密','ENCODE');

//解密
// $decode = authcode('我要解密','DECODE');

$auth_key = 34577 ; //密钥

function authcode($string, $operation, $key = '') {
     $key = md5($key ? $key : $GLOBALS['auth_key']);
     $key_length = strlen($key);
     $string = $operation == 'DECODE' ? base64_decode($string) : substr(md5($string.$key), 0, 8).$string;
     $string_length = strlen($string);
     $rndkey = $box = array();
     $result = '';
     for($i = 0; $i <= 255; $i++) {
             $rndkey[$i] = ord($key[$i % $key_length]);
             $box[$i] = $i;
     }
     for($j = $i = 0; $i < 256; $i++) {
             $j = ($j + $box[$i] + $rndkey[$i]) % 256;
             $tmp = $box[$i];
             $box[$i] = $box[$j];
             $box[$j] = $tmp;
     }
     for($a = $j = $i = 0; $i < $string_length; $i++) {
             $a = ($a + 1) % 256;
             $j = ($j + $box[$a]) % 256;
             $tmp = $box[$a];
             $box[$a] = $box[$j];
             $box[$j] = $tmp;
             $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
     }
     if($operation == 'DECODE') {
             if(substr($result, 0, 8) == substr(md5(substr($result, 8).$key), 0, 8)) {
                 return substr($result, 8);
             } else {
                 return '';
             }
     } else {
             return str_replace('=', '', base64_encode($result));
     }
}