<?php
$authkey = '';
/**
 * @param string $string: 輸入的需要加密（或解密）的明文（或密文）
 * @param string $operation: 'DECODE'或其它，其中默認表示解密，輸入其它表示加密
 * @param string $key: 加解密密鑰
 * @param int $expiry: 有效期
 */
function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {
  global $authkey;
  $ckey_length = 4;
  $key = md5($key != '' ? $key : $authkey);
  $keya = md5(substr($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));
  }
}
$str = '1234';
$key = '1234';
echo "明文:".$str;
echo "<br />";
echo "密鑰:".$key;
$encode = authcode($str,'11',$key);
echo "<br />";
echo "加密后的密文:".$encode;
echo "<br />";
$decode = authcode($encode,'DECODE',$key);
echo "解密后的明文:".$decode;
/*End of php*/