code: public function RC4($data)
      {
          $len = strlen($data);
          for ($c = 0; $c < $len; ++$c) {
              $this->i = ($this->i + 1) % 256;
              $this->j = ($this->j + $this->s[$this->i]) % 256;
              $t = $this->s[$this->i];
              $this->s[$this->i] = $this->s[$this->j];
              $this->s[$this->j] = $t;
  
              $t = ($this->s[$this->i] + $this->s[$this->j]) % 256;
  
              $data[$c] = chr(ord($data[$c]) ^ $this->s[$t]);
          }
  
          return $data;
      }
docs: Symmetric decryption/encryption function.
  
  @param string $data Data to encrypt/decrypt
  
  @return string