Hello,
вт, 3 сент. 2019 г. в 20:05, Niels Möller <ni...@lysator.liu.se>:
>
> dbarysh...@gmail.com writes:
>
> > From: Dmitry Eremin-Solenikov <dbarysh...@gmail.com>
> >
> > Add common implementations for functions doing XOR over
> > nettle_block16/nettle_block8.
>
> I've merged the first two patches. Thanks! Do you know if anyone is using
> GCM_TABLE_BITS 4? I've tested that it still works, both before and after
> your change, but I don't test it regularly.
I don't know. As the size difference between GCM_TABLE_BITS being 4 and 8
is not that big, maybe we can drop it alltogether. I can send a patch ;-)
> > +static inline void
> > +block16_xor_bytes (union nettle_block16 *r,
> > + const union nettle_block16 *x,
> > + const uint8_t *bytes)
> > +{
> > + memxor3 (r->b, x->b, bytes, 16);
> > +}
>
> [...]
>
> > +static inline void
> > +block8_xor_bytes (union nettle_block8 *r,
> > + const union nettle_block8 *x,
> > + const uint8_t *bytes)
> > +{
> > + memxor3 (r->b, x->b, bytes, 8);
> > +}
>
> Not sure these two wrappers are that helpful. Do you have a good
> reason to add them?
They fit into cmac128/cmac64/siv-cmac code, as they simplify code
there a bit. Using them you just say that Block1 = Block2 ^
bytestring, rather than XORing Block.b fields.
If you'd like, I can drop them, but from my point of view they look
like good encapsulation.
>
> The rest of the patch looks like a nice consolidation.
>
> > --- a/gcm.c
> > +++ b/gcm.c
> > @@ -53,16 +53,10 @@
> > #include "nettle-internal.h"
> > #include "macros.h"
> > #include "ctr-internal.h"
> > +#include "block-internal.h"
> >
> > #define GHASH_POLYNOMIAL 0xE1UL
> >
> > -static void
> > -gcm_gf_add (union nettle_block16 *r,
> > - const union nettle_block16 *x, const union nettle_block16 *y)
> > -{
> > - r->u64[0] = x->u64[0] ^ y->u64[0];
> > - r->u64[1] = x->u64[1] ^ y->u64[1];
> > -}
> > /* Multiplication by 010...0; a big-endian shift right. If the bit
> > shifted out is one, the defining polynomial is added to cancel it
> > out. r == x is allowed. */
> > @@ -108,7 +102,7 @@ gcm_gf_mul (union nettle_block16 *x, const union
> > nettle_block16 *y)
> > for (j = 0; j < 8; j++, b <<= 1)
> > {
> > if (b & 0x80)
> > - gcm_gf_add(&Z, &Z, &V);
> > + block16_xor3(&Z, &Z, &V);
>
> This and few other calls below can be block16_xor rather than block16_xor3.
Will fix in next iteration.
--
With best wishes
Dmitry
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