PHP encryption and decryption string functions

 

    / * **************************** ******************** 
    function name: DeCode 
    function operates: encryption and decryption string 
    Usage: 
    encryption: DeCode ( 'daichao', ' E', 'daichao') ; 
    decryption: DeCode ( 'the encrypted string', 'D', 'daichao '); 
    parameters: 
    $ string: required cryptographic string 
    $ operation: Analyzing encryption or decryption: E: encryption D: decrypting 
    $ key: encryption key (key); 
    *************************************** **************************************************************** * / public static function DeCode ( $ String , $ Operation , $ Key = '')    {$key=md5($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($result,8);
            }
else
            {
return'';
            }
        }
else
        {
return str_replace('=','',base64_encode($result));
        }
    }

Reproduced in: https: //www.cnblogs.com/200831856/archive/2008/11/28/1343531.html