PHP implements rc4 encryption algorithm code

Code
Copy code The code is as follows:
/*
* rc4 encryption algorithm
* $pwd key
* $data Data to be encrypted
*/
function rc4 ($pwd, $data)//$pwd key$ data needs to be encrypted 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;
}