/* -*-c-*-
*
- * $Id: gfshare.c,v 1.7 2001/06/16 23:42:17 mdw Exp $
+ * $Id$
*
* Secret sharing over %$\gf{2^8}$%
*
* (c) 2000 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: gfshare.c,v $
- * Revision 1.7 2001/06/16 23:42:17 mdw
- * Typesetting fixes.
- *
- * Revision 1.6 2000/12/06 20:30:10 mdw
- * Change secret sharing interface: present the secret at share
- * construction time.
- *
- * Revision 1.5 2000/06/24 19:11:47 mdw
- * Fix daft error in the comment for @gfshare_get@.
- *
- * Revision 1.4 2000/06/24 18:29:05 mdw
- * Interface change: allow shares to be extracted from a context on demand,
- * rather than building them all up-front.
- *
- * Revision 1.3 2000/06/22 18:04:13 mdw
- * Improve secret reconstruction -- compute coefficients as needed rather
- * than making a big array of them.
- *
- * Revision 1.2 2000/06/18 23:12:15 mdw
- * Change typesetting of Galois Field names.
- *
- * Revision 1.1 2000/06/17 10:56:30 mdw
- * Fast but nonstandard secret sharing system.
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include <assert.h>
/*----- Static variables --------------------------------------------------*/
-static octet gflog[] = GFSHARE_LOG, gfexp[] = GFSHARE_EXP;
+static const octet gflog[] = GFSHARE_LOG, gfexp[] = GFSHARE_EXP;
/*----- Main code ---------------------------------------------------------*/
}
}
+/* --- @gfshare_addedp@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to sharing context
+ * @unsigned x@ = which share number to check
+ *
+ * Returns: Nonzero if share @x@ has been added already, zero if it
+ * hasn't.
+ */
+
+int gfshare_addedp(gfshare *s, unsigned x)
+{
+ unsigned i;
+
+ for (i = 0; i < s->i; i++) {
+ if (GFSHARE_INDEX(s, i) == x + 1)
+ return (1);
+ }
+ return (0);
+}
+
/* --- @gfshare_add@ --- *
*
* Arguments: @gfshare *s@ = pointer to sharing context
{
octet *p;
+ assert(((void)"Share context is full", s->i < s->t));
+ assert(((void)"Share already present", !gfshare_addedp(s, x)));
+
/* --- If no vector has been allocated, create one --- */
if (!s->v) {
s->i = 0;
}
- assert(((void)"Share context is full", s->i < s->t));
-
/* --- Store the share in the vector --- */
- p = s->v + s->i * (s->sz + 1);
+ p = &GFSHARE_INDEX(s, s->i);
*p++ = x + 1;
memcpy(p, y, s->sz);
s->i++;
for (i = 0; i < s->t; i++) {
octet *p = buf;
- octet *q = s->v + i * (s->sz + 1);
+ octet *q = &GFSHARE_INDEX(s, i);
unsigned c = 0, ci = 0;
/* --- Compute the magic coefficient --- */
for (j = 0; j < s->t; j++) {
if (i == j)
continue;
- xj = s->v[j * (s->sz + 1)];
+ xj = GFSHARE_INDEX(s, j);
c += gflog[xj];
if (c >= 0xff)
c -= 0xff;