PHP methods for file operations and string encryption

<?php
  function RandAbc($length=""){//返回随机字符串
  $str="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
  return str_shuffle($str);
 }
 $filepath=&#39;index.php&#39;;
 $path_parts= pathinfo($filepath);
 $filename=$path_parts["basename"];
 $T_k1=RandAbc();//随机密匙1
 $T_k2=RandAbc();//随机密匙2
 $vstr=file_get_contents($filename);//要加密的文件 
 $v1=base64_encode($vstr);
 $c=strtr($v1,$T_k1,$T_k2);//根据密匙替换对应字符。
 $c=$T_k1.$T_k2.$c;
 $q1="O00O0O";
 $q2="O0O000";
 $q3="O0OO00";
 $q4="OO0O00";
 $q5="OO0000";
 $q6="O00OO0";
 $s=&#39;$&#39;.$q6.&#39;=urldecode("%6E1%7A%62%2F%6D%615%5C%76%740%6928%2D%70%78%75%71%79%2A6%6C%72%6B%64%679%5F%65%68%63%73%77%6F4%2B%6637%6A");$&#39;.$q1.&#39;=$&#39;.$q6.&#39;{3}.$&#39;.$q6.&#39;{6}.$&#39;.$q6.&#39;{33}.$&#39;.$q6.&#39;{30};$&#39;.$q3.&#39;=$&#39;.$q6.&#39;{33}.$&#39;.$q6.&#39;{10}.$&#39;.$q6.&#39;{24}.$&#39;.$q6.&#39;{10}.$&#39;.$q6.&#39;{24};$&#39;.$q4.&#39;=$&#39;.$q3.&#39;{0}.$&#39;.$q6.&#39;{18}.$&#39;.$q6.&#39;{3}.$&#39;.$q3.&#39;{0}.$&#39;.$q3.&#39;{1}.$&#39;.$q6.&#39;{24};$&#39;.$q5.&#39;=$&#39;.$q6.&#39;{7}.$&#39;.$q6.&#39;{13};$&#39;.$q1.&#39;.=$&#39;.$q6.&#39;{22}.$&#39;.$q6.&#39;{36}.$&#39;.$q6.&#39;{29}.$&#39;.$q6.&#39;{26}.$&#39;.$q6.&#39;{30}.$&#39;.$q6.&#39;{32}.$&#39;.$q6.&#39;{35}.$&#39;.$q6.&#39;{26}.$&#39;.$q6.&#39;{30};eval($&#39;.$q1.&#39;("&#39;.base64_encode(&#39;$&#39;.$q2.&#39;="&#39;.$c.&#39;";eval(\&#39;?>\&#39;.$&#39;.$q1.&#39;($&#39;.$q3.&#39;($&#39;.$q4.&#39;($&#39;.$q2.&#39;,$&#39;.$q5.&#39;*2),$&#39;.$q4.&#39;($&#39;.$q2.&#39;,$&#39;.$q5.&#39;,$&#39;.$q5.&#39;),$&#39;.$q4.&#39;($&#39;.$q2.&#39;,0,$&#39;.$q5.&#39;))));&#39;).&#39;"));&#39;;
 $s=&#39;<?
 &#39;.$s.
&#39;
 ?>&#39;;
 echo $s;
 //生成 加密后的PHP文件
 !is_dir(&#39;create/&#39;) && mkdir(&#39;create/&#39;);
 $fpp1 = fopen(&#39;create/&#39;.$filename,&#39;w&#39;);
 fwrite($fpp1,$s) or die(&#39;写文件错误&#39;);
 echo &#39;加密成功！&#39;;