Timing Cryptanalysis Attack

[Perry E. Metzger]

Tom Weinstein writes:
> > I for one will probably add a flag for conditional compilation of my
> > bignumber library so that it will take constant time.  This may be a
> > %10 slow down (using small windows exponentiation) which is trivial
> > compared to the %30 speedup I will probably get when I implement a
> > faster mod function :-).
> 
> Careful.  Even if you can make the number of executed instructions the
> same, you still have to worry about timing differences due to branches
> and the way the hardware multiplier handles different operands.

The trivial way to handle this is simply to check user time with the
right system calls and make sure it always comes out the same with an
apropriate number of sleeps.

Perry