aestab.c

来自「aes加解密算法源代码」· C语言 代码 · 共 385 行 · 第 1/2 页

#include "aestab.h"

#if defined(FIXED_TABLES)

/* implemented in case of wrong call for fixed tables */

void gen_tabs(void)
{
}

#else   /* dynamic table generation */

#if !defined(FF_TABLES)

/*  Generate the tables for the dynamic table option

    It will generally be sensible to use tables to compute finite
    field multiplies and inverses but where memory is scarse this
    code might sometimes be better. But it only has effect during
    initialisation so its pretty unimportant in overall terms.
*/

/*  return 2 ^ (n - 1) where n is the bit number of the highest bit
    set in x with x in the range 1 < x < 0x00000200.   This form is
    used so that locals within fi can be bytes rather than words
*/

static aes_08t hibit(const aes_32t x)
{   aes_08t r = (aes_08t)((x >> 1) | (x >> 2));

    r |= (r >> 2);
    r |= (r >> 4);
    return (r + 1) >> 1;
}

/* return the inverse of the finite field element x */

static aes_08t fi(const aes_08t x)
{   aes_08t p1 = x, p2 = BPOLY, n1 = hibit(x), n2 = 0x80, v1 = 1, v2 = 0;

    if(x < 2) return x;

    for(;;)
    {
        if(!n1) return v1;

        while(n2 >= n1)
        {
            n2 /= n1; p2 ^= p1 * n2; v2 ^= v1 * n2; n2 = hibit(p2);
        }

        if(!n2) return v2;

        while(n1 >= n2)
        {
            n1 /= n2; p1 ^= p2 * n1; v1 ^= v2 * n1; n1 = hibit(p1);
        }
    }
}

#endif

/* The forward and inverse affine transformations used in the S-box */

#define fwd_affine(x) \
    (w = (aes_32t)x, w ^= (w<<1)^(w<<2)^(w<<3)^(w<<4), 0x63^(aes_08t)(w^(w>>8)))

#define inv_affine(x) \
    (w = (aes_32t)x, w = (w<<1)^(w<<3)^(w<<6), 0x05^(aes_08t)(w^(w>>8)))

static int init = 0;

void gen_tabs(void)
{   aes_32t  i, w;

#if defined(FF_TABLES)

    aes_08t  pow[512], log[256];

    if(init) return;
    /*  log and power tables for GF(2^8) finite field with
        WPOLY as modular polynomial - the simplest primitive
        root is 0x03, used here to generate the tables
    */

    i = 0; w = 1;
    do
    {
        pow[i] = (aes_08t)w;
        pow[i + 255] = (aes_08t)w;
        log[w] = (aes_08t)i++;
        w ^=  (w << 1) ^ (w & 0x80 ? WPOLY : 0);
    }
    while (w != 1);

#else
    if(init) return;
#endif

    for(i = 0, w = 1; i < RC_LENGTH; ++i)
    {
        t_set(r,c)[i] = bytes2word(w, 0, 0, 0);
        w = f2(w);
    }

    for(i = 0; i < 256; ++i)
    {   aes_08t    b;

        b = fwd_affine(fi((aes_08t)i));
        w = bytes2word(f2(b), b, b, f3(b));

#if defined( SBX_SET )
        t_set(s,box)[i] = b;
#endif

#if defined( FT1_SET )                 /* tables for a normal encryption round */
        t_set(f,n)[i] = w;
#endif
#if defined( FT4_SET )
        t_set(f,n)[0][i] = w;
        t_set(f,n)[1][i] = upr(w,1);
        t_set(f,n)[2][i] = upr(w,2);
        t_set(f,n)[3][i] = upr(w,3);
#endif
        w = bytes2word(b, 0, 0, 0);

#if defined( FL1_SET )                 /* tables for last encryption round (may also   */
        t_set(f,l)[i] = w;        /* be used in the key schedule)                 */
#endif
#if defined( FL4_SET )
        t_set(f,l)[0][i] = w;
        t_set(f,l)[1][i] = upr(w,1);
        t_set(f,l)[2][i] = upr(w,2);
        t_set(f,l)[3][i] = upr(w,3);
#endif

#if defined( LS1_SET )                 /* table for key schedule if t_set(f,l) above is    */
        t_set(l,s)[i] = w;      /* not of the required form                     */
#endif
#if defined( LS4_SET )
        t_set(l,s)[0][i] = w;
        t_set(l,s)[1][i] = upr(w,1);
        t_set(l,s)[2][i] = upr(w,2);
        t_set(l,s)[3][i] = upr(w,3);
#endif

        b = fi(inv_affine((aes_08t)i));
        w = bytes2word(fe(b), f9(b), fd(b), fb(b));

#if defined( IM1_SET )                 /* tables for the inverse mix column operation  */
        t_set(i,m)[b] = w;
#endif
#if defined( IM4_SET )
        t_set(i,m)[0][b] = w;
        t_set(i,m)[1][b] = upr(w,1);
        t_set(i,m)[2][b] = upr(w,2);
        t_set(i,m)[3][b] = upr(w,3);
#endif

#if defined( ISB_SET )
        t_set(i,box)[i] = b;
#endif
#if defined( IT1_SET )                 /* tables for a normal decryption round */
        t_set(i,n)[i] = w;
#endif
#if defined( IT4_SET )
        t_set(i,n)[0][i] = w;
        t_set(i,n)[1][i] = upr(w,1);
        t_set(i,n)[2][i] = upr(w,2);
        t_set(i,n)[3][i] = upr(w,3);
#endif
        w = bytes2word(b, 0, 0, 0);
#if defined( IL1_SET )                 /* tables for last decryption round */
        t_set(i,l)[i] = w;
#endif
#if defined( IL4_SET )
        t_set(i,l)[0][i] = w;
        t_set(i,l)[1][i] = upr(w,1);
        t_set(i,l)[2][i] = upr(w,2);
        t_set(i,l)[3][i] = upr(w,3);
#endif
    }
    init = 1;
}

#endif

#if defined(__cplusplus)
}
#endif