従来の PHP 暗号化および復号化関数 Authcode() 共有

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($operation == &#39;DECODE&#39;) { 
  if((substr($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; 
 } 
}