--- /dev/null
+/* -*-c-*-
+ *
+ * Shamir's secret sharing
+ *
+ * (c) 2000 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------*
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * 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.
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "grand.h"
+#include "mp.h"
+#include "mpint.h"
+#include "mpbarrett.h"
+#include "mprand.h"
+#include "pgen.h"
+#include "rabin.h"
+#include "share.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @share_create@ --- *
+ *
+ * Arguments: @share *s@ = pointer to share context to initialize
+ * @unsigned t@ = threshold for the system
+ *
+ * Returns: ---
+ *
+ * Use: Initializes a sharing context.
+ */
+
+void share_create(share *s, unsigned t)
+{
+ s->t = t;
+ s->i = 0;
+ s->p = 0;
+ s->v = 0;
+}
+
+/* --- @share_destroy@ --- *
+ *
+ * Arguments: @share *s@ = pointer to share context to destroy
+ *
+ * Returns: ---
+ *
+ * Use: Disposes of a sharing context. All memory is freed, all
+ * integers are dropped.
+ */
+
+void share_destroy(share *s)
+{
+ unsigned i;
+
+ /* --- Dispose of the share vector --- */
+
+ if (s->v) {
+ for (i = 0; i < s->t; i++)
+ mp_drop(s->v[i].y);
+ xfree(s->v);
+ }
+
+ /* --- Other stuff --- */
+
+ 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@ 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, mp *n)
+{
+ unsigned i;
+
+ /* --- If there's no prime, construct one --- */
+
+ if (!s->p) {
+ pgen_filterctx pf;
+ rabin pr;
+ mp *p;
+ unsigned bits = (mp_octets(n) + 1) * 8;
+
+ pf.step = 2;
+ p = mprand(MP_NEW, bits, r, 1);
+ s->p = pgen("p", p, p, 0, 0, 0, pgen_filter, &pf,
+ rabin_iters(bits), pgen_test, &pr);
+ }
+
+ /* --- Construct the polynomial --- */
+
+ if (!s->v)
+ 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(n);
+}
+
+/* --- @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.
+ */
+
+mp *share_get(share *s, mp *d, unsigned x)
+{
+ mpbarrett mb;
+ mpw uw = x + 1;
+ mp u;
+ unsigned i;
+
+ /* --- Various bits of initialization --- */
+
+ mp_build(&u, &uw, &uw + 1);
+ mp_drop(d);
+
+ /* --- Evaluate the polynomial at %$x = i + 1$% --- */
+
+ 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);
+
+ 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 x@ = which share number this is
+ * @mp *y@ = the share value
+ *
+ * Returns: Number of shares required before recovery may be performed.
+ *
+ * Use: Adds a share to the context. The context must have been
+ * initialized with the correct prime @p@ and threshold @t@.
+ */
+
+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;
+ }
+
+ /* --- Store the share in the vector --- */
+
+ s->v[s->i].x = x + 1;
+ s->v[s->i].y = mp_copy(y);
+ s->i++;
+
+ /* --- Done --- */
+
+ return (s->t - s->i);
+}
+
+/* --- @share_combine@ --- *
+ *
+ * Arguments: @share *s@ = pointer to share context
+ *
+ * Returns: The secret, as a multiprecision integer.
+ *
+ * Use: Reconstructs a secret, given enough shares.
+ */
+
+mp *share_combine(share *s)
+{
+ mp *a = MP_ZERO;
+ mpbarrett mb;
+ unsigned i, j;
+ mp ii, jj;
+ mpw iiw, jjw;
+ mp *m = MP_NEW;
+
+ /* --- Sanity checking --- */
+
+ assert(((void)"Not enough shares yet", s->i == s->t));
+
+ /* --- Initialization --- */
+
+ 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_ONE;
+
+ iiw = s->v[i].x;
+ for (j = 0; j < s->t; j++) {
+ if (i == j)
+ continue;
+ jjw = s->v[j].x;
+ if (s->v[j].x >= s->v[i].x)
+ m = mp_sub(m, &jj, &ii);
+ else {
+ m = mp_sub(m, &ii, &jj);
+ m = mp_sub(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);
+ c = mpbarrett_reduce(&mb, c, c);
+ }
+ 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 = mpbarrett_reduce(&mb, a, a);
+ mp_drop(m);
+ mpbarrett_destroy(&mb);
+ return (a);
+}
+
+/*----- Test rig ----------------------------------------------------------*/
+
+#ifdef TEST_RIG
+
+#include "fibrand.h"
+
+static int verify(grand *r)
+{
+ unsigned n = r->ops->range(r, 16) + 8;
+ unsigned t = r->ops->range(r, n - 1) + 1;
+ unsigned len = r->ops->range(r, 160);
+
+ mp **v = xmalloc(t * sizeof(mp *));
+ unsigned *p = xmalloc(n * sizeof(unsigned));
+ mp *sec = mprand(MP_NEW, len, r, 0);
+ share s;
+ mp *pp;
+ mp *ss;
+ unsigned i;
+
+ int ok = 1;
+
+ for (i = 0; i < n; i++)
+ p[i] = i;
+ for (i = 0; i < t; i++) {
+ unsigned long j = r->ops->range(r, n - i);
+ unsigned x = p[i];
+ p[i] = p[i + j];
+ p[i + j] = x;
+ }
+
+ 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);
+
+ share_create(&s, t);
+ s.p = pp;
+ for (i = 0; i < t; i++)
+ share_add(&s, p[i], v[i]);
+ ss = share_combine(&s);
+ share_destroy(&s);
+
+ if (!MP_EQ(sec, ss)) {
+ ok = 0;
+ fprintf(stderr, "\nbad recombination of shares\n");
+ };
+
+ mp_drop(sec);
+ mp_drop(ss);
+
+ for (i = 0; i < t; i++)
+ mp_drop(v[i]);
+
+ xfree(v);
+ xfree(p);
+
+ assert(mparena_count(MPARENA_GLOBAL) + mparena_count(MPARENA_SECURE) == 0);
+ return (ok);
+}
+
+int main(void)
+{
+ grand *r = fibrand_create(0);
+ unsigned i;
+ int ok = 1;
+
+ fputs("share: ", stdout);
+ for (i = 0; i < 40; i++) {
+ if (!verify(r))
+ ok = 0;
+ fputc('.', stdout);
+ fflush(stdout);
+ }
+
+ if (ok)
+ fputs(" ok\n", stdout);
+ else
+ fputs(" failed\n", stdout);
+ return (ok ? EXIT_SUCCESS : EXIT_FAILURE);
+}
+
+#endif
+
+/*----- That's all, folks -------------------------------------------------*/
projects / u / mdw / catacomb / blobdiff