php implementation of rc4 encryption algorithm code

 
/* 
* rc4 The encryption algorithm  
* $pwd  The key  
* $data  Data to be encrypted  
*/ 
function rc4 ($pwd, $data)//$pwd The key $data To encrypt a string  
{ 
$key[] =""; 
$box[] =""; 
$pwd_length = strlen($pwd); 
$data_length = strlen($data); 
for ($i = 0; $i < 256; $i++) 
{ 
$key[$i] = ord($pwd[$i % $pwd_length]); 
$box[$i] = $i; 
} 
for ($j = $i = 0; $i < 256; $i++) 
{ 
$j = ($j + $box[$i] + $key[$i]) % 256; 
$tmp = $box[$i]; 
$box[$i] = $box[$j]; 
$box[$j] = $tmp; 
} 
for ($a = $j = $i = 0; $i < $data_length; $i++) 
{ 
$a = ($a + 1) % 256; 
$j = ($j + $box[$a]) % 256; 
$tmp = $box[$a]; 
$box[$a] = $box[$j]; 
$box[$j] = $tmp; 
$k = $box[(($box[$a] + $box[$j]) % 256)]; 
$cipher .= chr(ord($data[$i]) ^ $k); 
} 

return $cipher; 
}