/* -*-c-*-
*
- * $Id: share.c,v 1.1 2000/06/17 12:09:38 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 1.1 2000/06/17 12:09:38 mdw
- * Shamir's secret sharing system.
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include <stdio.h>
#include "grand.h"
#include "mp.h"
#include "mpint.h"
-#include "mpmont.h"
+#include "mpbarrett.h"
#include "mprand.h"
#include "pgen.h"
#include "rabin.h"
/* --- @share_create@ --- *
*
* Arguments: @share *s@ = pointer to share context to initialize
- * @unsigned t, n@ = threshold parameters for the system
+ * @unsigned t@ = threshold for the system
*
* Returns: ---
*
* Use: Initializes a sharing context.
*/
-void share_create(share *s, unsigned t, unsigned n)
+void share_create(share *s, unsigned t)
{
s->t = t;
- s->n = n;
s->i = 0;
- s->s = 0;
s->p = 0;
s->v = 0;
}
void share_destroy(share *s)
{
- unsigned n;
unsigned i;
/* --- Dispose of the share vector --- */
if (s->v) {
- if (s->i)
- n = s->i;
- else if (s->n)
- n = s->n;
- else
- n = s->t;
- for (i = 0; i < n; 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: Generates @c->n@ secret shares, such that any @c->t@ of them
- * may be used to recover the secret.
- *
+ * Use: Initializes a sharing context to be able to create shares.
* The context structure is expected to be mostly filled in. In
- * particular, @t@, @n@ 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)
{
- mp **v;
unsigned i;
- mp *u;
- mpmont mm;
/* --- If there's no prime, construct one --- */
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);
rabin_iters(bits), pgen_test, &pr);
}
- /* --- Construct the coefficients --- */
+ /* --- Construct the polynomial --- */
- mpmont_create(&mm, s->p);
- v = xmalloc(s->t * sizeof(mp *));
+ if (!s->v)
+ s->v = xmalloc(s->t * sizeof(share_pt));
for (i = 0; i < s->t - 1; i++)
- v[i] = mprand_range(MP_NEW, s->p, r, 0);
- v[s->t - 1] = mpmont_mul(&mm, MP_NEW, s->s, mm.r2);
-
- /* --- Construct the shares --- */
+ s->v[i].y = mprand_range(MP_NEWSEC, s->p, r, 0);
+ s->v[s->t - 1].y = mp_copy(n);
+}
- if (!s->v)
- s->v = xmalloc(s->n * sizeof(share_pt));
+/* --- @share_get@ --- *
+ *
+ * Arguments: @share *s@ = pointer to share conext
+ * @mp *d@ = destination for the share
+ * @unsigned x@ = share index to fetch
+ *
+ * Returns: The share, as requested.
+ *
+ * Use: Extracts a share from the system. You may extract @MPW_MAX@
+ * shares, or @s->p@ shares from the system, whichever is
+ * smaller. Shares are indexed from 0.
+ */
- u = mp_copy(mm.r);
- for (i = 0; i < s->n; i++) {
- mp *m = MP_ZERO;
- unsigned j;
+mp *share_get(share *s, mp *d, unsigned x)
+{
+ mpbarrett mb;
+ mpw uw = x + 1;
+ mp u;
+ unsigned i;
- /* --- Evaluate the polynomial at %$x = i + 1$% --- */
+ /* --- Various bits of initialization --- */
- for (j = 0; j < s->t; j++) {
- m = mpmont_mul(&mm, m, m, u);
- m = mp_add(m, m, v[j]);
- if (MP_CMP(m, >=, s->p))
- m = mp_sub(m, m, s->p);
- }
+ mp_build(&u, &uw, &uw + 1);
+ mp_drop(d);
- /* --- Reduce the final result --- */
+ /* --- Evaluate the polynomial at %$x = i + 1$% --- */
- s->v[i].x = i;
- s->v[i].y = mpmont_reduce(&mm, m, m);
+ d = MP_ZERO;
+ mpbarrett_create(&mb, s->p);
+ for (i = 0; i < s->t; i++) {
+ d = mp_mul(d, d, &u);
+ d = mp_add(d, d, s->v[i].y);
+ d = mpbarrett_reduce(&mb, d, d);
+ }
+ mpbarrett_destroy(&mb);
- /* --- Compute the next point in Montgomery space --- */
+ return (d);
+}
- u = mp_add(u, u, mm.r);
- if (MP_CMP(u, >=, s->p))
- u = mp_sub(u, u, s->p);
- }
- mpmont_destroy(&mm);
+/* --- @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.
+ */
- /* --- Dispose of various bits of old rubbish --- */
+int share_addedp(share *s, unsigned x)
+{
+ unsigned i;
- for (i = 0; i < s->t; i++)
- mp_drop(v[i]);
- mp_drop(u);
- xfree(v);
+ for (i = 0; i < s->i; i++) {
+ if (s->v[i].x == x + 1)
+ return (1);
+ }
+ return (0);
}
/* --- @share_add@ --- *
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) {
+ unsigned i;
s->v = xmalloc(s->t * sizeof(share_pt));
s->i = 0;
+ for (i = 0; i < s->t; i++)
+ 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;
+ s->v[s->i].x = x + 1;
s->v[s->i].y = mp_copy(y);
s->i++;
mp *share_combine(share *s)
{
mp *a = MP_ZERO;
- mpmont mm;
+ mpbarrett mb;
unsigned i, j;
- mp *ii = MP_NEW, *jj = MP_NEW;
+ mp ii, jj;
+ mpw iiw, jjw;
mp *m = MP_NEW;
/* --- Sanity checking --- */
/* --- Initialization --- */
- mpmont_create(&mm, s->p);
+ mpbarrett_create(&mb, s->p);
+ mp_build(&ii, &iiw, &iiw + 1);
+ mp_build(&jj, &jjw, &jjw + 1);
/* --- Grind through the shares --- */
for (i = 0; i < s->t; i++) {
- mp *c = mp_copy(mm.r);
+ mp *c = MP_ONE;
- ii = mp_fromuint(ii, s->v[i].x + 1);
+ iiw = s->v[i].x;
for (j = 0; j < s->t; j++) {
if (i == j)
continue;
- jj = mp_fromuint(jj, s->v[j].x + 1);
+ jjw = s->v[j].x;
if (s->v[j].x >= s->v[i].x)
- m = mp_sub(m, jj, ii);
+ m = mp_sub(m, &jj, &ii);
else {
- m = mp_sub(m, ii, jj);
+ m = mp_sub(m, &ii, &jj);
m = mp_sub(m, s->p, m);
}
- jj = mpmont_mul(&mm, jj, jj, mm.r2);
- mp_gcd(0, 0, &m, s->p, m);
- m = mpmont_mul(&mm, m, m, mm.r2);
- m = mpmont_mul(&mm, m, m, jj);
- c = mpmont_mul(&mm, c, c, 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);
+ c = mpbarrett_reduce(&mb, c, c);
}
- m = mpmont_mul(&mm, m, s->v[i].y, mm.r2);
- c = mpmont_mul(&mm, c, c, m);
+ c = mp_mul(c, c, s->v[i].y);
+ c = mpbarrett_reduce(&mb, c, c);
a = mp_add(a, a, c);
mp_drop(c);
}
- a = mpmont_reduce(&mm, a, a);
- s->s = mp_copy(a);
- mp_drop(ii);
- if (jj)
- mp_drop(jj);
+ a = mpbarrett_reduce(&mb, a, a);
mp_drop(m);
- mpmont_destroy(&mm);
+ mpbarrett_destroy(&mb);
return (a);
}
unsigned t = r->ops->range(r, n - 1) + 1;
unsigned len = r->ops->range(r, 160);
- share_pt *v = xmalloc(t * sizeof(share_pt));
+ mp **v = xmalloc(t * sizeof(mp *));
unsigned *p = xmalloc(n * sizeof(unsigned));
mp *sec = mprand(MP_NEW, len, r, 0);
share s;
p[i + j] = x;
}
- share_create(&s, t, n);
- s.s = mp_copy(sec);
- share_mkshares(&s, r);
- for (i = 0; i < t; i++) {
- v[i].x = s.v[p[i]].x;
- v[i].y = mp_copy(s.v[p[i]].y);
- }
+ share_create(&s, t);
+ 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);
share_destroy(&s);
+ assert(mparena_count(MPARENA_GLOBAL) + mparena_count(MPARENA_SECURE) == t + 2);
- assert(mparena_count(MPARENA_GLOBAL) == t + 2);
-
- share_create(&s, t, n);
+ share_create(&s, t);
s.p = pp;
- for (i = 0; i < t; i++) {
- share_add(&s, v[i].x, v[i].y);
- }
+ for (i = 0; i < t; i++)
+ share_add(&s, p[i], v[i]);
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");
};
mp_drop(ss);
for (i = 0; i < t; i++)
- mp_drop(v[i].y);
+ mp_drop(v[i]);
xfree(v);
xfree(p);
- assert(mparena_count(MPARENA_GLOBAL) == 0);
+ assert(mparena_count(MPARENA_GLOBAL) + mparena_count(MPARENA_SECURE) == 0);
return (ok);
}
projects / u / mdw / catacomb / blobdiff