//set dec value - sn certificate
	$dec = '96103344898673588835476';
	// init hex array
	$hex = array();
	while ($dec) {
		// get modulus // based on docs both params are string
		$modulus = bcmod($dec, '16');
		// convert to hex and prepend to array
		array_unshift($hex, dechex($modulus));
		// update decimal number
		$dec = bcdiv(bcsub($dec, $modulus), 16);
	}

	// array elements to string
	$hex_sn = implode('', $hex);