The problem with coarsening timers is that many things can be used as one. Performance registers, received packet timing are just the obvious ones.
This problem has been studied a lot. The venerable TCSEC Rainbow Series dedicates an entire volume to covert channels (the light pink one iirc).
It is a statistical problem. Even if you reduce the timing precision or randomize it and effectively raise the noise floor, it just takes a little bit longer for the attacker to get his data.
A good analogy would be Differential Power Analysis (DPA). Measurements are collected over a period of time to enhance the signal.
This problem has been studied a lot. The venerable TCSEC Rainbow Series dedicates an entire volume to covert channels (the light pink one iirc).
It is a statistical problem. Even if you reduce the timing precision or randomize it and effectively raise the noise floor, it just takes a little bit longer for the attacker to get his data.
A good analogy would be Differential Power Analysis (DPA). Measurements are collected over a period of time to enhance the signal.