X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/5d4fee2a9d2ecf4d2566c0deca27e1878bf2380f..cd6eca4375f46a35b93e2fea4b0428a23b451aa3:/share.c

diff --git a/share.c b/share.c
index cc793db..1afa189 100644
--- a/share.c
+++ b/share.c
@@ -1,13 +1,13 @@
 /* -*-c-*-
  *
- * $Id: share.c,v 1.5 2000/12/06 20:30:10 mdw Exp $
+ * $Id$
  *
  * Shamir's secret sharing
  *
  * (c) 2000 Straylight/Edgeware
  */
 
-/*----- Licensing notice --------------------------------------------------* 
+/*----- Licensing notice --------------------------------------------------*
  *
  * This file is part of Catacomb.
  *
@@ -15,41 +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: share.c,v $
- * 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>
@@ -102,17 +79,14 @@ void share_destroy(share *s)
   /* --- Dispose of the share vector --- */
 
   if (s->v) {
-    for (i = 0; i < s->t; i++) {
-      if (s->v[i].y)
-	mp_drop(s->v[i].y);
-    }
+    for (i = 0; i < s->t; i++)
+      mp_drop(s->v[i].y);
     xfree(s->v);
   }
 
   /* --- Other stuff --- */
 
-  if (s->p)
-    mp_drop(s->p);
+  mp_drop(s->p);
 }
 
 /* --- @share_mkshares@ --- *
@@ -182,8 +156,7 @@ mp *share_get(share *s, mp *d, unsigned x)
   /* --- Various bits of initialization --- */
 
   mp_build(&u, &uw, &uw + 1);
-  if (d)
-    mp_drop(d);
+  mp_drop(d);
 
   /* --- Evaluate the polynomial at %$x = i + 1$% --- */
 
@@ -199,6 +172,26 @@ mp *share_get(share *s, mp *d, unsigned x)
   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
@@ -213,6 +206,9 @@ mp *share_get(share *s, mp *d, unsigned x)
 
 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) {
@@ -223,8 +219,6 @@ unsigned share_add(share *s, unsigned x, mp *y)
       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;
@@ -280,7 +274,7 @@ mp *share_combine(share *s)
 	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);
@@ -293,8 +287,7 @@ mp *share_combine(share *s)
   }
 
   a = mpbarrett_reduce(&mb, a, a);
-  if (m)
-    mp_drop(m);
+  mp_drop(m);
   mpbarrett_destroy(&mb);
   return (a);
 }