> Open question: should the class file respond to DiscardBytes? I kinda feel
> like it should be a nop, but there could be folks who want to call it to
> increase their comfort level.
>
> The promise of DiscardBytes() is, well, to discard bytes. If this actually
> makes sense from a security standpoint or efficiency stand point is not at
> us to judge, or we wouldn't have created this function in the first place.
> If the user wants to discard 500 bytes, let him do this via DiscardBytes()
> or he'll just write DiscardBytes() himself.
>
If I parsed this correctly, then you want DiscardBytes to perform the
discard.
Here's the updated implementations. Its optimized for word/register-sized
discards.
//! generate and discard n bytes.
void RDRAND::DiscardBytes(size_t n)
{
assert(Ready());
#if CRYPTOPP_BOOL_X64 || CRYPTOPP_BOOL_X32
static const size_t SIZE = 128/sizeof(word64);
FixedSizeSecBlock<word64, SIZE> discard;
#else
static const size_t SIZE = 128/sizeof(word32);
FixedSizeSecBlock<word32, SIZE> discard;
#endif
size_t count = STDMIN(n, discard.SizeInBytes());
while (count)
{
GenerateBlock(discard.BytePtr(), count);
n -= count;
count = STDMIN(n, discard.SizeInBytes());
}
}
GenerateBlock can throw, so callers will need to be aware of the potential
side effects of the discard.
Jeff
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