PHP implements rc4 encryption algorithm

The decryption method of this algorithm is to re-encrypt once and then it can be restored. .

 /*
 * 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;
 }