Added method to set random local port

[luigigubello]

Added method to set a (pseudo)random local port, so that the board needs not to use always the same embedded local port for receiving NTP packets.

At the moment, the variable port is a constant embedded value used by the board for receiving NTP packets via unencrypted UDP connection. Changing randomly port to receive NTP packets doesn't improve cryptographic security and it is not the final solution, but it adds a layer to make harder the attacker's job.

How to use

void setup() {
  ...
}
void loop() {
  timeClient.setRandomPort();
  timeClient.update();
}

How it works

setRandomPort() sets a pseudorandom port and NTPClient::update() launches NTPClient.begin(port) if port is different by default value NTP_DEFAULT_LOCAL_PORT

[aentinger]

Great change, small corrections necessary ;)

[aentinger]

Hi @luigigubello 👋 ☕ Is there any special reason why you change this data type from int to long? Certainly int is capable of holding values up 2^16-1 even on AVR 😉

[luigigubello]

Certainly int is capable of holding values up 2^16-1 even on AVR

Reading the documentation I have understood it's not, but your suggestion to use unsigned int is a good idea. So, yes, I have chosen long instead int to be sure to maintain the AVR compatibility. It seems unsigned int is the best choice 🙂

[aentinger]

I've checked again - so yes, int 2 byte on AVR which covers from -2^15 to 2^15-1. unsigned int covers 0 to 2^16-1 which is enough.

[aentinger]

Same here ... I think int or even better unsigned int (as it excludes negative values) would do the job just nicely here.

[luigigubello]

I think you are right