public static String deviceIdToMac(String deviceId) {
		if (deviceId.length() != 20) {
			return "";
		}
		String macStr = deviceId.substring(8, 20);
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < 12; i++) {
			sb.append(macStr.charAt(i));
			if (i % 2 == 1) {
				sb.append(":");
			}
		}
		sb.deleteCharAt(sb.length()-1);
		return sb.toString();
	}