Re: 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 <[EMAIL PROTECTED]>
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.
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Kevin Elliott <mailto:kelliott@;mac.com> ICQ#23758827