Exemple #1
0
/* this is a shell function that calls either the normal or Montgomery
 * exptmod functions.  Originally the call to the montgomery code was
 * embedded in the normal function but that wasted alot of stack space
 * for nothing (since 99% of the time the Montgomery code would be called)
 */
int mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
{
  int dr;

  /* modulus P must be positive */
  if (P->sign == MP_NEG) {
     return MP_VAL;
  }

  /* if exponent X is negative we have to recurse */
  if (X->sign == MP_NEG) {
     mp_int tmpG, tmpX;
     int err;

     /* first compute 1/G mod P */
     if ((err = mp_init(&tmpG)) != MP_OKAY) {
        return err;
     }
     if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) {
        mp_clear(&tmpG);
        return err;
     }

     /* now get |X| */
     if ((err = mp_init(&tmpX)) != MP_OKAY) {
        mp_clear(&tmpG);
        return err;
     }
     if ((err = mp_abs(X, &tmpX)) != MP_OKAY) {
        mp_clear_multi(&tmpG, &tmpX, NULL);
        return err;
     }

     /* and now compute (1/G)**|X| instead of G**X [X < 0] */
     err = mp_exptmod(&tmpG, &tmpX, P, Y);
     mp_clear_multi(&tmpG, &tmpX, NULL);
     return err;
  }

  /* is it a DR modulus? */
  dr = mp_dr_is_modulus(P);

  /* if not, is it a uDR modulus? */
  if (dr == 0) {
     dr = mp_reduce_is_2k(P) << 1;
  }
    
  /* if the modulus is odd or dr != 0 use the fast method */
#ifndef NO_FAST_EXPTMOD
  if (mp_isodd (P) == 1 || dr !=  0) {
    return mp_exptmod_fast (G, X, P, Y, dr);
  }
  else
#endif
  {
    /* otherwise use the generic Barrett reduction technique */
    return s_mp_exptmod (G, X, P, Y);
  }
}
Exemple #2
0
/* this is a shell function that calls either the normal or Montgomery
 * exptmod functions.  Originally the call to the montgomery code was
 * embedded in the normal function but that wasted alot of stack space
 * for nothing (since 99% of the time the Montgomery code would be called)
 */
int mp_exptmod(const mp_int *G, const mp_int *X, const mp_int *P, mp_int *Y)
{
   int dr;

   /* modulus P must be positive */
   if (P->sign == MP_NEG) {
      return MP_VAL;
   }

   /* if exponent X is negative we have to recurse */
   if (X->sign == MP_NEG) {
#ifdef BN_MP_INVMOD_C
      mp_int tmpG, tmpX;
      int err;

      /* first compute 1/G mod P */
      if ((err = mp_init(&tmpG)) != MP_OKAY) {
         return err;
      }
      if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) {
         mp_clear(&tmpG);
         return err;
      }

      /* now get |X| */
      if ((err = mp_init(&tmpX)) != MP_OKAY) {
         mp_clear(&tmpG);
         return err;
      }
      if ((err = mp_abs(X, &tmpX)) != MP_OKAY) {
         mp_clear_multi(&tmpG, &tmpX, NULL);
         return err;
      }

      /* and now compute (1/G)**|X| instead of G**X [X < 0] */
      err = mp_exptmod(&tmpG, &tmpX, P, Y);
      mp_clear_multi(&tmpG, &tmpX, NULL);
      return err;
#else
      /* no invmod */
      return MP_VAL;
#endif
   }

   /* modified diminished radix reduction */
#if defined(BN_MP_REDUCE_IS_2K_L_C) && defined(BN_MP_REDUCE_2K_L_C) && defined(BN_S_MP_EXPTMOD_C)
   if (mp_reduce_is_2k_l(P) == MP_YES) {
      return s_mp_exptmod(G, X, P, Y, 1);
   }
#endif

#ifdef BN_MP_DR_IS_MODULUS_C
   /* is it a DR modulus? */
   dr = mp_dr_is_modulus(P);
#else
   /* default to no */
   dr = 0;
#endif

#ifdef BN_MP_REDUCE_IS_2K_C
   /* if not, is it a unrestricted DR modulus? */
   if (dr == 0) {
      dr = mp_reduce_is_2k(P) << 1;
   }
#endif

   /* if the modulus is odd or dr != 0 use the montgomery method */
#ifdef BN_MP_EXPTMOD_FAST_C
   if ((mp_isodd(P) == MP_YES) || (dr !=  0)) {
      return mp_exptmod_fast(G, X, P, Y, dr);
   } else {
#endif
#ifdef BN_S_MP_EXPTMOD_C
      /* otherwise use the generic Barrett reduction technique */
      return s_mp_exptmod(G, X, P, Y, 0);
#else
      /* no exptmod for evens */
      return MP_VAL;
#endif
#ifdef BN_MP_EXPTMOD_FAST_C
   }
#endif
}