/* -*-c-*-
*
- * $Id: gfshare.c,v 1.4 2000/06/24 18:29:05 mdw Exp $
+ * $Id$
*
- * Secret sharing over %$\gf(2^8)$%
+ * 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 1.4 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 ---------------------------------------------------------*/
s->t = t;
s->i = 0;
s->sz = sz;
- s->s = 0;
s->v = 0;
}
*
* Arguments: @gfshare *s@ = pointer to share context to fill in
* @grand *r@ = pointer to random number source
+ * @const void *buf@ = pointer to the secret to share
*
* Returns: ---
*
* Use: Initializes a sharing context to be able to create shares.
* The context structure is expected to be mostly filled in. In
- * particular, @t@ and @s@ must be initialized. If @v@ is zero,
- * a vector of appropriate size is allocated. You should use
- * the macro @GFSHARE_INIT@ or @gfshare_create@ to construct
- * sharing contexts.
+ * particular, @t@ must be initialized. If @v@ is zero, a
+ * vector of appropriate size is allocated. You should use the
+ * macro @GFSHARE_INIT@ or @gfshare_create@ to construct sharing
+ * contexts.
*/
-void gfshare_mkshares(gfshare *s, grand *r)
+void gfshare_mkshares(gfshare *s, grand *r, const void *buf)
{
s->v = XS_ALLOC(s->sz * s->t);
r->ops->fill(r, s->v, s->sz * (s->t - 1));
- memcpy(s->v + s->sz * (s->t - 1), s->s, s->sz);
+ memcpy(s->v + s->sz * (s->t - 1), buf, s->sz);
}
/* --- @gfshare_get@ --- *
* @unsigned x@ = share index to fetch
* @void *buf@ = pointer to output buffer
*
- * Returns: The share, as requested.
+ * Returns: ---
*
* Use: Extracts a share from the system. You may extract up to 255
* shares from the system. Shares are indexed from 0.
}
}
+/* --- @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;
r->ops->fill(r, sec, len);
gfshare_create(&s, t, len);
- s.s = sec;
- gfshare_mkshares(&s, r);
+ gfshare_mkshares(&s, r, sec);
for (i = 0; i < t; i++)
gfshare_get(&s, p[i], v + (i * len));
gfshare_destroy(&s);
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