Re: [PATCH v2 05/38] crypto/aes: Add constants for ShiftRows, InvShiftRows

[Richard Henderson]

On 6/29/23 12:21, Ard Biesheuvel wrote:
> > +/* AES ShiftRows, for complete unrolling. */
> > +enum {
> > +    AES_SH_0 = 0x0,
> > +    AES_SH_1 = 0x5,
> > +    AES_SH_2 = 0xa,
> > +    AES_SH_3 = 0xf,
> > +    AES_SH_4 = 0x4,
> > +    AES_SH_5 = 0x9,
> > +    AES_SH_6 = 0xe,
> > +    AES_SH_7 = 0x3,
> > +    AES_SH_8 = 0x8,
> > +    AES_SH_9 = 0xd,
> > +    AES_SH_A = 0x2,
> > +    AES_SH_B = 0x7,
> > +    AES_SH_C = 0xc,
> > +    AES_SH_D = 0x1,
> > +    AES_SH_E = 0x6,
> > +    AES_SH_F = 0xb,
> > +};
> > +
>
> We might simplify this further by doing
>
> #define AES_SH(n)  (((n) * 5) % 16)
> #define AES_ISH(n)  (((n) * 13) % 16)

Thanks.  I should have noticed, but

  s'_{r,c} = s_{r,(c+r)%4}

didn't make an impression and I assumed the table was non-regular.


r~