UCenter is an authcode code for a reversible cryptographic function

 
function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) { 

$ckey_length = 4; //The random key length is 0-32;
//Add a random key, can make the ciphertext without any rules, even if the original text and the key are exactly the same, the encryption result will be different each time, increase the crack difficulty.
//The larger the value, the greater the rule of ciphertext change, ciphertext change = 16 to the power of $ckey_length
//When this value is 0, no random key is generated

$key = md5($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 ''; 
} 
} else { 
return $keyc.str_replace('=', '', base64_encode($result)); 
} 
} 
 
$string = authcode("Hello","ENCODE","HTML_TCCJ_AUTH"); 
echo $string,'<br/>'; 
echo authcode($string,"DECODE","HTML_TCCJ_AUTH"),'<br/>';