/* -*-c-*-
*
- * $Id: mpmont-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
+ * $Id$
*
* Modular exponentiation with Montgomery reduction
*
* (c) 2004 Straylight/Edgeware
*/
-/*----- Licensing notice --------------------------------------------------*
+/*----- Licensing notice --------------------------------------------------*
*
* This file is part of Catacomb.
*
* it under the terms of the GNU Library General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
- *
+ *
* Catacomb is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Library General Public License for more details.
- *
+ *
* You should have received a copy of the GNU Library General Public
* License along with Catacomb; if not, write to the Free
* Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
-/*----- Revision history --------------------------------------------------*
- *
- * $Log: mpmont-exp.c,v $
- * Revision 1.1 2004/04/01 12:50:09 mdw
- * Add cyclic group abstraction, with test code. Separate off exponentation
- * functions for better static linking. Fix a buttload of bugs on the way.
- * Generally ensure that negative exponents do inversion correctly. Add
- * table of standard prime-field subgroups. (Binary field subgroups are
- * currently unimplemented but easy to add if anyone ever finds a good one.)
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include "mp.h"
MP_COPY(a);
MP_SHRINK(e);
- if (e->f & MP_NEG) {
- mp *g = MP_NEW;
- a = mpmont_reduce(mm, a, a);
- mp_gcd(&g, 0, &a, mm->m, a);
- assert(MP_EQ(g, MP_ONE));
- a = mpmont_mul(mm, a, a, mm->r2);
- mp_drop(g);
- }
- if (MP_LEN(e) == 0)
+ if (MP_ZEROP(e))
;
- else if (MP_LEN(e) < EXP_THRESH)
- EXP_SIMPLE(x, a, e);
- else
- EXP_WINDOW(x, a, e);
+ else {
+ if (MP_NEGP(e)) {
+ a = mpmont_reduce(mm, a, a);
+ a = mp_modinv(a, a, mm->m);
+ a = mpmont_mul(mm, a, a, mm->r2);
+ }
+ if (MP_LEN(e) < EXP_THRESH)
+ EXP_SIMPLE(x, a, e);
+ else
+ EXP_WINDOW(x, a, e);
+ }
mp_drop(d);
mp_drop(spare);
mp_drop(a);
return ok;
}
-
static test_chunk tests[] = {
{ "exp", texp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
{ 0, 0, { 0 } },