Re: [PATCH 04/35] crypto: Add aesenc_SB_SR

[Richard Henderson]

On 6/3/23 06:15, Ard Biesheuvel wrote:
> > diff --git a/crypto/aes.c b/crypto/aes.c
> > index 1309a13e91..708838315a 100644
> > --- a/crypto/aes.c
> > +++ b/crypto/aes.c
> > @@ -29,6 +29,7 @@
> >    */
> >   #include "qemu/osdep.h"
> >   #include "crypto/aes.h"
> > +#include "crypto/aes-round.h"
> >
> >   typedef uint32_t u32;
> >   typedef uint8_t u8;
> > @@ -1251,6 +1252,52 @@ static const u32 rcon[] = {
> >           0x1B000000, 0x36000000, /* for 128-bit blocks, Rijndael never uses 
> > more than 10 rcon values */
> >   };
> >
> > +/* Perform SubBytes + ShiftRows. */
> > +static inline void
> > +aesenc_SB_SR_swap(AESState *r, const AESState *st, bool swap)
> > +{
> > +    const int swap_b = swap ? 15 : 0;
> > +    uint8_t t;
> > +
> > +    /* These four indexes are not swizzled. */
> > +    r->b[swap_b ^ 0x0] = AES_sbox[st->b[swap_b ^ AES_SH_0]];
> > +    r->b[swap_b ^ 0x4] = AES_sbox[st->b[swap_b ^ AES_SH_4]];
> > +    r->b[swap_b ^ 0x8] = AES_sbox[st->b[swap_b ^ AES_SH_8]];
> > +    r->b[swap_b ^ 0xc] = AES_sbox[st->b[swap_b ^ AES_SH_C]];
> > +
> > +    /* Otherwise, break cycles. */
> > +
>
> This is only needed it r == st, right?

Yes.  This is, perhaps, where using symbolic AES_SH_X while assuming knowledge of the 
value does not aid understanding.


r~

> > +    t = AES_sbox[st->b[swap_b ^ AES_SH_D]];
> > +    r->b[swap_b ^ 0x1] = AES_sbox[st->b[swap_b ^ AES_SH_1]];
> > +    r->b[swap_b ^ 0x5] = AES_sbox[st->b[swap_b ^ AES_SH_5]];
> > +    r->b[swap_b ^ 0x9] = AES_sbox[st->b[swap_b ^ AES_SH_9]];
> > +    r->b[swap_b ^ 0xd] = t;
> > +
> > +    t = AES_sbox[st->b[swap_b ^ AES_SH_A]];
> > +    r->b[swap_b ^ 0x2] = AES_sbox[st->b[swap_b ^ AES_SH_2]];
> > +    r->b[swap_b ^ 0xa] = t;
> > +
> > +    t = AES_sbox[st->b[swap_b ^ AES_SH_E]];
> > +    r->b[swap_b ^ 0x6] = AES_sbox[st->b[swap_b ^ AES_SH_6]];
> > +    r->b[swap_b ^ 0xe] = t;
> > +
> > +    t = AES_sbox[st->b[swap_b ^ AES_SH_7]];
> > +    r->b[swap_b ^ 0x3] = AES_sbox[st->b[swap_b ^ AES_SH_3]];
> > +    r->b[swap_b ^ 0xf] = AES_sbox[st->b[swap_b ^ AES_SH_F]];
> > +    r->b[swap_b ^ 0xb] = AES_sbox[st->b[swap_b ^ AES_SH_B]];
> > +    r->b[swap_b ^ 0x7] = t;
> > +}
> > +
> > +void aesenc_SB_SR_gen(AESState *r, const AESState *st)
> > +{
> > +    aesenc_SB_SR_swap(r, st, false);
> > +}
> > +
> > +void aesenc_SB_SR_genrev(AESState *r, const AESState *st)
> > +{
> > +    aesenc_SB_SR_swap(r, st, true);
> > +}
> > +
> >   /**
> >    * Expand the cipher key into the encryption key schedule.
> >    */
> > --
> > 2.34.1