php加密解密字符串

php 加密解密字符串

//函数名称:encrypt   函数作用:加密解密字符串
//加密     :encrypt('str','E','lama');
//解密     :encrypt('被加密过的字符串','D','lama');
function encrypt($string,$operation='E',$key='kxs'){
  $src  = array("/","+","=");
  $dist = array("_a","_b","_c");
  if($operation=='D'){$string  = str_replace($dist,$src,$string);}
  $key=md5($key);
  $key_length=strlen($key);
  $string=$operation=='D'?base64_decode($string):substr(md5($string.$key),0,8).$string;
  $string_length=strlen($string);
  $rndkey=$box=array();
  $result='';
  for($i=0;$i<=255;$i++)
  {
    $rndkey[$i]=ord($key[$i%$key_length]);
    $box[$i]=$i;
  }
  for($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($operation=='D')
  {
    if(substr($result,0,8)==substr(md5(substr($result,8).$key),0,8))
    {
      return substr($result,8);
    }
    else
    {
      return'';
    }
  }
  else
  {
    $rdate  = str_replace('=','',base64_encode($result));
    $rdate  = str_replace($src,$dist,$rdate);
    return $rdate;
  }
}