3 ms·
If there's timing information leaked by the implementation then non-deterministic interference by things like GC pauses (CPU load, network traffic, etc) are noi
by bmm6o 12y ago
If there's timing information leaked by the implementation then non-deterministic interference by things like GC pauses (CPU load, network traffic, etc) are noise that raises the work effort of the attack but does not in general make it impossible. This is why "introduce a random sleep" is a terrible defense to a timing attack. Statistics doesn't care about the cause of the variability, if there are samples coming from different populations it can detect that.
- jamesaguilar 12y ago> terrible defense In what sense? In the sense of not mathematically fixing the problem, or in the sense of leaving it feasible to exploit in reality?
- bmm6o 12y agoBoth, unless I don't understand the distinction you're trying to make. The problem is that the law of large numbers is on the attacker's side. If the attacker gets N tries his statistical power goes as sqrt(N), which means that to stay safe the variance in your random delay has to be large enough to cover that. That is, if d is the timing difference between the slow path and the fast path and the attacker gets N tries, the variance in your random delay has to be on the order of d sqrt(N). This is huge even for modest values of N.