经典PHP加密解密函数Authcode()修复版代码，加密解密authcode

function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0){
 
 if($operation == 'DECODE') {
 $string = str_replace('[a]','+',$string);
 $string = str_replace('[b]','&',$string);
 $string = str_replace('[c]','/',$string);
 }
 $ckey_length = 4;
 $key = md5($key ? $key : 'livcmsencryption ');
 $keya = md5(substr($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 {
 $ustr = $keyc.str_replace('=', '', base64_encode($result));
 $ustr = str_replace('+','[a]',$ustr);
 $ustr = str_replace('&','[b]',$ustr);
 $ustr = str_replace('/','[c]',$ustr);
  return $ustr;
 }
}