经典PHP加密解密函数Authcode()修复版代码

Authcode这个函数很多人都使用，这函数来自Discuz程序，用于加密解密字符串，可以设置钥匙（key）和过期时间，在很多时候都用得着。原版的函数代码可能会生成+、/、&这样的字符，导致通过URL传值取回时被转义，导致无法解密。火端网络稍加修改，把这几个字符替换成其它字符，解密时再替换回去，这样就完美了！

代码如下：

    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;
     }
    }