/* -*-c-*-
*
- * $Id: share.c,v 1.3 2000/06/24 18:29:05 mdw Exp $
+ * $Id$
*
* Shamir's secret sharing
*
* (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: share.c,v $
- * 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>
{
s->t = t;
s->i = 0;
- s->s = 0;
s->p = 0;
s->v = 0;
}
/* --- 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);
- if (s->s)
- mp_drop(s->s);
+ mp_drop(s->p);
}
/* --- @share_mkshares@ --- *
*
* Arguments: @share *s@ = pointer to share context to fill in
* @grand *r@ = pointer to random number source
+ * @mp *n@ = 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 @p@ is zero,
- * a prime number of appropriate size is generated
- * automatically. If @v@ is zero, a vector of appropriate size
- * is allocated. You should use the macro @SHARE_INIT@ or
- * @share_create@ to construct sharing contexts.
+ * particular, @t@ must be initialized. If @p@ is zero, a prime
+ * number of appropriate size is generated automatically. If
+ * @v@ is zero, a vector of appropriate size is allocated. You
+ * should use the macro @SHARE_INIT@ or @share_create@ to
+ * construct sharing contexts.
*/
-void share_mkshares(share *s, grand *r)
+void share_mkshares(share *s, grand *r, mp *n)
{
unsigned i;
pgen_filterctx pf;
rabin pr;
mp *p;
- unsigned bits = (mp_octets(s->s) + 1) * 8;
+ unsigned bits = (mp_octets(n) + 1) * 8;
pf.step = 2;
p = mprand(MP_NEW, bits, r, 1);
s->v = xmalloc(s->t * sizeof(share_pt));
for (i = 0; i < s->t - 1; i++)
s->v[i].y = mprand_range(MP_NEWSEC, s->p, r, 0);
- s->v[s->t - 1].y = mp_copy(s->s);
+ s->v[s->t - 1].y = mp_copy(n);
}
/* --- @share_get@ --- *
/* --- Various bits of initialization --- */
mp_build(&u, &uw, &uw + 1);
- if (d)
- mp_drop(d);
+ mp_drop(d);
/* --- Evaluate the polynomial at %$x = i + 1$% --- */
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);
}
a = mpbarrett_reduce(&mb, a, a);
- s->s = mp_copy(a);
- if (m)
- mp_drop(m);
+ mp_drop(m);
mpbarrett_destroy(&mb);
return (a);
}
}
share_create(&s, t);
- s.s = mp_copy(sec);
- share_mkshares(&s, r);
+ share_mkshares(&s, r, sec);
for (i = 0; i < t; i++)
v[i] = share_get(&s, MP_NEW, p[i]);
pp = mp_copy(s.p);
ss = share_combine(&s);
share_destroy(&s);
- if (MP_CMP(sec, !=, ss)) {
+ if (!MP_EQ(sec, ss)) {
ok = 0;
fprintf(stderr, "\nbad recombination of shares\n");
};
projects / u / mdw / catacomb / blobdiff