X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/34e4f738bcba58e6d8c4cabbb0b3232a65b42a9d..f52f2db067dc1388b16ab00ddb53e26a381a6e3e:/mpmont.c

diff --git a/mpmont.c b/mpmont.c
index 926fde8..65b3fcc 100644
--- a/mpmont.c
+++ b/mpmont.c
@@ -1,13 +1,13 @@
 /* -*-c-*-
  *
- * $Id: mpmont.c,v 1.17 2004/04/01 12:50:09 mdw Exp $
+ * $Id$
  *
  * Montgomery reduction
  *
  * (c) 1999 Straylight/Edgeware
  */
 
-/*----- Licensing notice --------------------------------------------------* 
+/*----- Licensing notice --------------------------------------------------*
  *
  * This file is part of Catacomb.
  *
@@ -15,88 +15,18 @@
  * 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.c,v $
- * Revision 1.17  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.)
- *
- * Revision 1.16  2002/01/13 13:40:31  mdw
- * Avoid trashing arguments before we've used them.
- *
- * Revision 1.15  2001/06/16 13:00:20  mdw
- * Use the generic exponentiation functions.
- *
- * Revision 1.14  2001/02/22 09:04:26  mdw
- * Cosmetic fix.
- *
- * Revision 1.13  2001/02/03 12:00:29  mdw
- * Now @mp_drop@ checks its argument is non-NULL before attempting to free
- * it.  Note that the macro version @MP_DROP@ doesn't do this.
- *
- * Revision 1.12  2000/10/08 15:48:35  mdw
- * Rename Karatsuba constants now that we have @gfx_kmul@ too.
- *
- * Revision 1.11  2000/10/08 12:04:27  mdw
- * (mpmont_reduce, mpmont_mul): Cope with negative numbers.
- *
- * Revision 1.10  2000/07/29 17:05:43  mdw
- * (mpmont_expr): Use sliding window exponentiation, with a drop-through
- * for small exponents to use a simple left-to-right bitwise routine.  This
- * can reduce modexp times by up to a quarter.
- *
- * Revision 1.9  2000/06/17 11:45:09  mdw
- * Major memory management overhaul.  Added arena support.  Use the secure
- * arena for secret integers.  Replace and improve the MP management macros
- * (e.g., replace MP_MODIFY by MP_DEST).
- *
- * Revision 1.8  1999/12/22 15:55:00  mdw
- * Adjust Karatsuba parameters.
- *
- * Revision 1.7  1999/12/11 01:51:14  mdw
- * Use a Karatsuba-based reduction for large moduli.
- *
- * Revision 1.6  1999/12/10 23:18:39  mdw
- * Change interface for suggested destinations.
- *
- * Revision 1.5  1999/11/22 13:58:40  mdw
- * Add an option to disable Montgomery reduction, so that performance
- * comparisons can be done.
- *
- * Revision 1.4  1999/11/21 12:27:06  mdw
- * Remove a division from the Montgomery setup by calculating
- * %$R^2 \bmod m$% first and then %$R \bmod m$% by Montgomery reduction of
- * %$R^2$%.
- *
- * Revision 1.3  1999/11/21 11:35:10  mdw
- * Performance improvement: use @mp_sqr@ and @mpmont_reduce@ instead of
- * @mpmont_mul@ for squaring in exponentiation.
- *
- * Revision 1.2  1999/11/19 13:17:26  mdw
- * Add extra interface to exponentiation which returns a Montgomerized
- * result.
- *
- * Revision 1.1  1999/11/17 18:02:16  mdw
- * New multiprecision integer arithmetic suite.
- *
- */
-
 /*----- Header files ------------------------------------------------------*/
 
 #include "mp.h"
@@ -119,7 +49,7 @@
  * Arguments:	@mpmont *mm@ = pointer to Montgomery reduction context
  *		@mp *m@ = modulus to use
  *
- * Returns:	---
+ * Returns:	Zero on success, nonzero on error.
  *
  * Use:		Initializes a Montgomery reduction context ready for use.
  *		The argument @m@ must be a positive odd integer.
@@ -127,32 +57,28 @@
 
 #ifdef MPMONT_DISABLE
 
-void mpmont_create(mpmont *mm, mp *m)
+int mpmont_create(mpmont *mm, mp *m)
 {
   mp_shrink(m);
   mm->m = MP_COPY(m);
   mm->r = MP_ONE;
   mm->r2 = MP_ONE;
   mm->mi = MP_ONE;
+  return (0);
 }
 
 #else
 
-void mpmont_create(mpmont *mm, mp *m)
+int mpmont_create(mpmont *mm, mp *m)
 {
   size_t n = MP_LEN(m);
   mp *r2 = mp_new(2 * n + 1, 0);
   mp r;
 
-  /* --- Validate the arguments --- */
-
-  assert(((void)"Montgomery modulus must be positive",
-	  (m->f & MP_NEG) == 0));
-  assert(((void)"Montgomery modulus must be odd", m->v[0] & 1));
-
   /* --- Take a copy of the modulus --- */
 
-  mp_shrink(m);
+ if (!MP_POSP(m) || !MP_ODDP(m))
+   return (-1);
   mm->m = MP_COPY(m);
 
   /* --- Determine %$R^2$% --- */
@@ -164,8 +90,7 @@ void mpmont_create(mpmont *mm, mp *m)
   /* --- Find the magic value @mi@ --- */
 
   mp_build(&r, r2->v + n, r2->vl);
-  mm->mi = MP_NEW;
-  mp_gcd(0, 0, &mm->mi, &r, m);
+  mm->mi = mp_modinv(MP_NEW, m, &r);
   mm->mi = mp_sub(mm->mi, &r, mm->mi);
 
   /* --- Discover the values %$R \bmod m$% and %$R^2 \bmod m$% --- */
@@ -174,6 +99,7 @@ void mpmont_create(mpmont *mm, mp *m)
   mp_div(0, &mm->r2, r2, m);
   mm->r = mpmont_reduce(mm, MP_NEW, mm->r2);
   MP_DROP(r2);
+  return (0);
 }
 
 #endif
@@ -404,7 +330,7 @@ static int tcreate(dstr *v)
     fputs("\n*** bad r", stderr);
     fputs("\nm = ", stderr); mp_writefile(m, stderr, 10);
     fputs("\nexpected ", stderr); mp_writefile(r, stderr, 10);
-    fputs("\n   found ", stderr); mp_writefile(mm.r, stderr, 10);
+    fputs("\n	found ", stderr); mp_writefile(mm.r, stderr, 10);
     fputc('\n', stderr);
     ok = 0;
   }
@@ -413,7 +339,7 @@ static int tcreate(dstr *v)
     fputs("\n*** bad r2", stderr);
     fputs("\nm = ", stderr); mp_writefile(m, stderr, 10);
     fputs("\nexpected ", stderr); mp_writefile(r2, stderr, 10);
-    fputs("\n   found ", stderr); mp_writefile(mm.r2, stderr, 10);
+    fputs("\n	found ", stderr); mp_writefile(mm.r2, stderr, 10);
     fputc('\n', stderr);
     ok = 0;
   }