ucenter reversible encryption function authcode usage example

<?php
//authcode加密函数
function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) { 

$ckey_length = 4; // 随机密钥长度 取值 0-32; 
// 加入随机密钥，可以令密文无任何规律，即便是原文和密钥完全相同，加密结果也会每次不同，增大破解难度。 
// 取值越大，密文变动规律越大，密文变化 = 16 的 $ckey_length 次方 
// 当此值为 0 时，则不产生随机密钥 

$key = md5($key ? $key : UC_KEY); 
$keya = md5(substr($key, 0, 16)); 
$keyb = md5(substr($key, 16, 16)); 
$keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length): substr(md5(microtime()), -$ckey_length)) : ''; 

$cryptkey = $keya.md5($keya.$keyc); 
$key_length = strlen($cryptkey); 

$string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0)
.substr(md5($string.$keyb), 0, 16).$string; 
$string_length = strlen($string); 

$result = ''; 
$box = range(0, 255); 

$rndkey = array(); 
for($i = 0; $i <= 255; $i++) { 
$rndkey[$i] = ord($cryptkey[$i % $key_length]); 
} 

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, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) ==
 substr(md5(substr($result, 26).$keyb), 0, 16)) { 
return substr($result, 26); 
} else { 
return ''; 
} // bbs.it-home.org
} else { 
return $keyc.str_replace('=', '', base64_encode($result)); 
} 
} 

//调用示例
$string = authcode("Hello","ENCODE","HTML_TCCJ_AUTH"); 
echo $string,'<br/>'; 
echo authcode($string,"DECODE","HTML_TCCJ_AUTH"),'<br/>';