X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/3d64a35c9b151e739eb6a8712915810ea574eac8..cd6eca4375f46a35b93e2fea4b0428a23b451aa3:/gfshare.c

diff --git a/gfshare.c b/gfshare.c
index 0af17cc..99b1223 100644
--- a/gfshare.c
+++ b/gfshare.c
@@ -1,13 +1,13 @@
 /* -*-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.
  *
@@ -15,37 +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: 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>
@@ -63,7 +44,7 @@
 
 /*----- Static variables --------------------------------------------------*/
 
-static octet gflog[] = GFSHARE_LOG, gfexp[] = GFSHARE_EXP;
+static const octet gflog[] = GFSHARE_LOG, gfexp[] = GFSHARE_EXP;
 
 /*----- Main code ---------------------------------------------------------*/
 
@@ -83,7 +64,6 @@ void gfshare_create(gfshare *s, unsigned t, size_t sz)
   s->t = t;
   s->i = 0;
   s->sz = sz;
-  s->s = 0;
   s->v = 0;
 }
 
@@ -108,22 +88,23 @@ void gfshare_destroy(gfshare *s)
  *
  * 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@ --- *
@@ -132,7 +113,7 @@ void gfshare_mkshares(gfshare *s, grand *r)
  *		@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.
@@ -161,6 +142,26 @@ void gfshare_get(gfshare *s, unsigned x, void *buf)
   }
 }
 
+/* --- @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
@@ -177,6 +178,9 @@ unsigned gfshare_add(gfshare *s, unsigned x, const void *y)
 {
   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) {
@@ -184,11 +188,9 @@ unsigned gfshare_add(gfshare *s, unsigned x, const void *y)
     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++;
@@ -223,7 +225,7 @@ void gfshare_combine(gfshare *s, void *buf)
 
   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 --- */
@@ -232,7 +234,7 @@ void gfshare_combine(gfshare *s, void *buf)
     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;
@@ -287,9 +289,8 @@ static int verify(grand *r)
   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);