a no-parts solution to seeding the routine is to use a closed
loop counter to trigger the WDT.  Because WDT is temperature-
sensitive, the LSB of the counter might be random enough for
use in seeding the rest of the routine.
alice

> > It works terrible fine. I bet that you can4t guess the value of a counter
> > that runs at 1Mhz.
>
> Sounds good when asynchronous and fast compared to the read-rate. Like in
> your particular implementation.
>
> A dangerous implementation would be to use the internal TMR of a controller
> instead of an asynchronous one.  Probably you have your keyboard reader
> in the TMR interrupt.  Probably you need a new "random" value when the
> user starts a game - by pressing the START _key_!  THAT would be a bad
> implementation of the (good) idea.
>
> When it comes to security/cryptography, you must avoid that the user can
> influence the random number algorithm.  In your example that could be
> to remove the external counter and replace it by his own generated signal,
> and thereby enforce the generation of weak session keys etc.