How did you calculate that? The question didn’t even mention a specific speed, just “near the speed of light”.

The kinetic energy for a grain of sand near the speed of light is somewhere between “quite a lot” and “literally infinity” (which is, in a sense, the reason you can’t actually reach light speed without a way to supply infinite energy).

Fair enough, I didn’t consider compute resources

The actual length of the password isn’t the problem. If they were “doing stuff right” then it would make no difference to them whether the password was 20 characters or 200, because once it was hashed both would be stored in the same amount of space.

The fact that they’ve specified a limit is strong evidence that they’renot doing it right