Did you *really* zeroize that key?

[Kevin Elliott]

At 19:30 +0000  on  11/7/02, David Howe wrote:
>at Thursday, November 07, 2002 6:13 PM, David Honig <dahonig at cox.net>
>was seen to say:
>>  Wouldn't a crypto coder be using paranoid-programming
>>  skills, like *checking* that the memory is actually zeroed?
>That is one of the workarounds yes - but of course a (theoretical)
>clever compiler could realise that
>
>int myflag;
>myflag=0;
>if (myflag!=0) { do stuff } ;
>
>can be optimised away entirely as the result is constant.
>
>the problem isn't so much a question of what would work now, but "is it
>possible that your zeros could be optimised away by a theoretical future
>compiler, and how do we make portable code that nevertheless can't be
>optimised away?"

The point is though, that according to C99 today

volatile int myflag;
myflag=0;
if (myflag!=0) { do stuff } ;

does _exactly_ what you want, per the spec.  The only compilers that 
don't work this way are by definition out of spec, so adding new 
stuff isn't going to help.

Having said that, most of what your talking about pragma wise is 
boils down to controlling the optimizer.  Most compilers offer 
options to control this, but it's vendor specific.  I can see how 
adding this to the spec would be worthwhile.  But it's not essential 
to fix the problem above.
-- 
_____________________________________________
Kevin Elliott <mailto:kelliott at mac.com> ICQ#23758827