Generate random message id.

[sbernard31]

About message ID, the CoAP specification say :

"4.4. Message Correlation ...
... Several implementation strategies can be employed for generating Message IDs. ... ... It is strongly recommended that the initial value of the variable (e.g., on startup) be randomized, in order to make successful off-path attacks on the protocol less likely."

So, I propose to replace the predictible way to generate message ID by using srand() and rand() from stdlib.

[dnav]

Hi,

Nice idea. However I can see two problems with your patch:

• the message ID is 16-bits long. So the result of rand() will be truncated and we might have collisions.
• Even if the rand() is limited to 16-bits, we will have collisions sooner than with a linear progression.

To be aligned with the CoAP specs, I would suggest to just initialize the lwm2m_contxt_t::nextMID with rand().

[sbernard31]

You're right, I will fix that :)

[dnav]

Project moved to http://github.com/eclipse/wakaama