Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Reader/Xls/RC4.php
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 $data;
    }
public function RC4($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;
    }
Symmetric decryption/encryption function.

@param string $data Data to encrypt/decrypt

@return string