/* -*-c-*-
*
- * $Id: share.c,v 1.6 2001/02/03 16:05:41 mdw Exp $
+ * $Id$
*
* Shamir's secret sharing
*
* MA 02111-1307, USA.
*/
-/*----- Revision history --------------------------------------------------*
- *
- * $Log: share.c,v $
- * Revision 1.6 2001/02/03 16:05:41 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 1.5 2000/12/06 20:30:10 mdw
- * Change secret sharing interface: present the secret at share
- * construction time.
- *
- * Revision 1.4 2000/10/08 12:16:17 mdw
- * Use @MP_EQ@ instead of @MP_CMP@.
- *
- * Revision 1.3 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 1.2 2000/06/18 23:05:19 mdw
- * Minor performance tweak: use Barrett reduction rather than Montgomery.
- * Fast secret sharing isn't done here, though: see `gfshare' instead.
- *
- * Revision 1.1 2000/06/17 12:09:38 mdw
- * Shamir's secret sharing system.
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include <stdio.h>
return (d);
}
+/* --- @share_addedp@ --- *
+ *
+ * Arguments: @share *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 share_addedp(share *s, unsigned x)
+{
+ unsigned i;
+
+ for (i = 0; i < s->i; i++) {
+ if (s->v[i].x == x + 1)
+ return (1);
+ }
+ return (0);
+}
+
/* --- @share_add@ --- *
*
* Arguments: @share *s@ = pointer to sharing context
unsigned share_add(share *s, unsigned x, mp *y)
{
+ assert(((void)"Share context is full", s->i < s->t));
+ assert(((void)"Share already present", !share_addedp(s, x)));
+
/* --- If no vector has been allocated, create one --- */
if (!s->v) {
s->v[i].y = 0;
}
- assert(((void)"Share context is full", s->i < s->t));
-
/* --- Store the share in the vector --- */
s->v[s->i].x = x + 1;
m = mp_sub(m, &ii, &jj);
m = mp_sub(m, s->p, m);
}
- mp_gcd(0, 0, &m, s->p, m);
+ m = mp_modinv(m, m, s->p);
c = mp_mul(c, c, &jj);
c = mpbarrett_reduce(&mb, c, c);
c = mp_mul(c, c, m);