Simo Sorce <s...@redhat.com> writes:
> Ok, I took a stab at removing xts_steal completely in the second patch,
> let me know what you think, I think I may like it better than my
> original code and uses nettle_block16 for temporary storage to avoid a
> copy.
I like the version without xts_steal.
It's slightly annoying to repeat duplicate code for a final complete
block, but no big deal. Alternative ways to do the final block of the
non-stealing case (including the case of exactly one block) are
for (; length >= 2 * XTS_BLOCK_SIZE || length == XTS_BLOCK_SIZE; ...)
{
...
}
if (length > 0)
{
... steal ...
}
or (since we require at least one block)
do {
...
length -= XTS_BLOCK_SIZE;
if (!length)
return;
} while (length >= 2*XTS_BLOCK_SIZE);
Do what you think makes it clearest.
For the tests, have you checked that there's coverage for the special
wraparound? I.e., that tests fail if the line
dst->b[0] ^= 0x87 & -carry;
is changed. Since there are a very small number of test vectors with
more than one block, we could be unlucky and have carry == 0 all the
time when xts_shift is called from the tests...
>> > +static void
>> > +check_length(size_t length, uint8_t *dst)
>> > +{
>> > + assert(length >= XTS_BLOCK_SIZE);
>> > + /* asserts may be compiled out, try to save the user by zeroing the dst
>> > in
>> > + * case the buffer contains sensitive data (like the clear text for
>> > inplace
>> > + * encryption) */
>> > + if (length < XTS_BLOCK_SIZE)
>> > + memxor(dst, dst, length);
>> > +}
Why memxor rather than memset?
Regards,
/Niels
--
Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677.
Internet email is subject to wholesale government surveillance.
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