--- /dev/null
+/* -*-c-*-
+ *
+ * $Id: gfshare-mktab.c,v 1.1 2000/06/17 10:56:30 mdw Exp $
+ *
+ * Generate tables for %$\gf(2^8)$% multiplication
+ *
+ * (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.
+ */
+
+/*----- Revision history --------------------------------------------------*
+ *
+ * $Log: gfshare-mktab.c,v $
+ * Revision 1.1 2000/06/17 10:56:30 mdw
+ * Fast but nonstandard secret sharing system.
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <mLib/bits.h>
+
+/*----- Magic numbers -----------------------------------------------------*/
+
+#define MOD 0x11d
+
+/*----- Main code ---------------------------------------------------------*/
+
+int main(int argc, char *argv[])
+{
+ octet log[256], alog[256];
+ unsigned x;
+ unsigned i;
+
+ x = 1;
+ for (i = 0; i < 255; i++) {
+ alog[i] = x;
+ log[x] = i;
+ x <<= 1;
+ if (x & 0x100)
+ x ^= MOD;
+ }
+ log[0] = 0;
+ alog[255] = 1;
+
+ fputs("\
+/* -*-c-*-\n\
+ *\n\
+ * Log tables for secret sharing in %$\\gf(2^8)$% [generated]\n\
+ */\n\
+\n\
+#ifndef GFSHARE_TAB_H\n\
+#define GFSHARE_TAB_H\n\
+\n\
+#define GFSHARE_LOG { \\\n\
+ ", stdout);
+
+ for (i = 0; i < 256; i++) {
+ printf("0x%02x", log[i]);
+ if (i == 255)
+ puts(" \\\n}\n");
+ else if (i % 8 == 7)
+ fputs(", \\\n ", stdout);
+ else
+ fputs(", ", stdout);
+ }
+
+ fputs("\
+#define GFSHARE_EXP { \\\n\
+ ", stdout);
+
+ for (i = 0; i < 510; i++) {
+ printf("0x%02x", alog[i % 255]);
+ if (i == 509)
+ puts(" \\\n}\n");
+ else if (i % 8 == 7)
+ fputs(", \\\n ", stdout);
+ else
+ fputs(", ", stdout);
+ }
+
+ /* --- Done --- */
+
+ fputs("#endif\n", stdout);
+
+ if (fclose(stdout)) {
+ fprintf(stderr, "error writing data\n");
+ exit(EXIT_FAILURE);
+ }
+
+ return (0);
+}
+
+/*----- That's all, folks -------------------------------------------------*/
--- /dev/null
+/* -*-c-*-
+ *
+ * $Id: gfshare.c,v 1.1 2000/06/17 10:56:30 mdw Exp $
+ *
+ * Secret sharing over %$gf(2^8)$%
+ *
+ * (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.
+ */
+
+/*----- Revision history --------------------------------------------------*
+ *
+ * $Log: gfshare.c,v $
+ * Revision 1.1 2000/06/17 10:56:30 mdw
+ * Fast but nonstandard secret sharing system.
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <assert.h>
+#include <stdarg.h>
+#include <stdio.h>
+
+#include <mLib/alloc.h>
+#include <mLib/bits.h>
+
+#include "arena.h"
+#include "gfshare.h"
+#include "gfshare-tab.h"
+#include "grand.h"
+
+/*----- Static variables --------------------------------------------------*/
+
+static octet gflog[] = GFSHARE_LOG, gfexp[] = GFSHARE_EXP;
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @gfshare_create@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context to initialize
+ * @unsigned t, n@ = threshold parameters for the system
+ * @size_t sz@ = size of the secret
+ *
+ * Returns: ---
+ *
+ * Use: Initializes a sharing context.
+ */
+
+void gfshare_create(gfshare *s, unsigned t, unsigned n, size_t sz)
+{
+ s->t = t;
+ s->n = n;
+ s->i = 0;
+ s->sz = sz;
+ s->s = 0;
+ s->v = 0;
+}
+
+/* --- @gfshare_destroy@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context to destroy
+ *
+ * Returns: ---
+ *
+ * Use: Disposes of a sharing context. The allocations for the
+ * individual shares and the vector @v@ are freed; the secret is
+ * left alone.
+ */
+
+void gfshare_destroy(gfshare *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)
+ XS_FREE(s->v[i].y);
+ }
+ xfree(s->v);
+ }
+}
+
+/* --- @gfshare_mkshares@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context to fill in
+ * @grand *r@ = pointer to random number source
+ *
+ * Returns: ---
+ *
+ * Use: Generates @c->n@ secret shares, such that any @c->t@ of them
+ * may be used to recover the secret.
+ *
+ * The context structure is expected to be mostly filled in. In
+ * particular, @t@, @n@, @ssz@ 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.
+ */
+
+void gfshare_mkshares(gfshare *s, grand *r)
+{
+ octet *v;
+ unsigned i;
+
+ /* --- Construct the coefficients --- */
+
+ v = XS_ALLOC(s->sz * s->t);
+ r->ops->fill(r, v, s->sz * (s->t - 1));
+ memcpy(v + s->sz * (s->t - 1), s->s, s->sz);
+
+
+ /* --- Construct the shares --- */
+
+ if (!s->v)
+ s->v = xmalloc(s->n * sizeof(gfshare_pt));
+
+ for (i = 0; i < s->n; i++) {
+ unsigned j;
+ const octet *p = v;
+ unsigned ilog = gflog[i + 1];
+
+ /* --- Evaluate the polynomial at %$x = i + 1$% --- */
+
+ s->v[i].y = XS_ALLOC(s->sz);
+ memcpy(s->v[i].y, p, s->sz);
+ p += s->sz;
+ for (j = 1; j < s->t; j++) {
+ octet *q = s->v[i].y;
+ unsigned k;
+ for (k = 0; k < s->sz; k++) {
+ unsigned qq = *q;
+ if (qq)
+ qq = gfexp[ilog + gflog[qq]];
+ *q++ = qq ^ *p++;
+ }
+ }
+ s->v[i].x = i;
+ }
+
+ /* --- Dispose of various bits of old rubbish --- */
+
+ XS_FREE(v);
+}
+
+/* --- @gfshare_add@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to sharing context
+ * @unsigned x@ = which share number this is
+ * @const octet *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 threshold @t@.
+ */
+
+unsigned gfshare_add(gfshare *s, unsigned x, const octet *y)
+{
+ /* --- If no vector has been allocated, create one --- */
+
+ if (!s->v) {
+ s->v = xmalloc(s->t * sizeof(gfshare_pt));
+ s->i = 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].y = XS_ALLOC(s->sz);
+ memcpy(s->v[s->i].y, y, s->sz);
+ s->i++;
+
+ /* --- Done --- */
+
+ return (s->t - s->i);
+}
+
+/* --- @gfshare_combine@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context
+ * @octet *buf@ = pointer to output buffer for the secret
+ *
+ * Returns: ---
+ *
+ * Use: Reconstructs a secret, given enough shares.
+ */
+
+void gfshare_combine(gfshare *s, octet *buf)
+{
+ unsigned i, j;
+ octet *v;
+
+ /* --- Sanity checking --- */
+
+ assert(((void)"Not enough shares yet", s->i == s->t));
+
+ /* --- Precomputation of coefficients --- */
+
+ v = XS_ALLOC(s->t);
+
+ for (i = 0; i < s->t; i++) {
+ unsigned c = 0, ci = 0;
+ for (j = 0; j < s->t; j++) {
+ if (i == j)
+ continue;
+ c += gflog[s->v[j].x + 1];
+ if (c >= 0xff)
+ c -= 0xff;
+ ci += gflog[(s->v[i].x + 1) ^ (s->v[j].x + 1)];
+ if (ci >= 0xff)
+ ci -= 0xff;
+ }
+ if (ci > c)
+ c += 0xff;
+ c -= ci;
+ v[i] = c;
+ }
+
+ /* --- Grind through the shares --- */
+
+ for (i = 0; i < s->sz; i++) {
+ unsigned x = 0;
+ for (j = 0; j < s->t; j++) {
+ if (s->v[j].y[i])
+ x ^= gfexp[v[j] + gflog[s->v[j].y[i]]];
+ }
+ buf[i] = x;
+ }
+
+ XS_FREE(v);
+}
+
+/*----- 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, 32) + 1;
+
+ gfshare_pt *v = xmalloc(t * sizeof(gfshare_pt));
+ unsigned *p = xmalloc(n * sizeof(unsigned));
+ octet *sec = xmalloc(len), *sbuf = xmalloc(len);
+ gfshare s;
+ 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;
+ }
+
+ r->ops->fill(r, sec, len);
+
+ gfshare_create(&s, t, n, len);
+ s.s = sec;
+
+ gfshare_mkshares(&s, r);
+ for (i = 0; i < t; i++) {
+ v[i].x = s.v[p[i]].x;
+ v[i].y = xmalloc(len);
+ memcpy(v[i].y, s.v[p[i]].y, len);
+ }
+ gfshare_destroy(&s);
+
+ gfshare_create(&s, t, n, len);
+ for (i = 0; i < t; i++) {
+ gfshare_add(&s, v[i].x, v[i].y);
+ }
+ gfshare_combine(&s, sbuf);
+ gfshare_destroy(&s);
+
+ if (memcmp(sec, sbuf, len) != 0) {
+ ok = 0;
+ fprintf(stderr, "\nbad recombination of shares\n");
+ };
+
+ xfree(sec);
+ xfree(sbuf);
+
+ for (i = 0; i < t; i++)
+ xfree(v[i].y);
+ xfree(v);
+ xfree(p);
+
+ return (ok);
+}
+
+int main(void)
+{
+ grand *r = fibrand_create(0);
+ unsigned i;
+ int ok = 1;
+
+ fputs("gfshare: ", 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 -------------------------------------------------*/
--- /dev/null
+/* -*-c-*-
+ *
+ * $Id: gfshare.h,v 1.1 2000/06/17 10:56:30 mdw Exp $
+ *
+ * Secret sharing over %$\gf(2^8)$%
+ *
+ * (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.
+ */
+
+/*----- Revision history --------------------------------------------------*
+ *
+ * $Log: gfshare.h,v $
+ * Revision 1.1 2000/06/17 10:56:30 mdw
+ * Fast but nonstandard secret sharing system.
+ *
+ */
+
+#ifndef CATACOMB_GFSHARE_H
+#define CATACOMB_GFSHARE_H
+
+#ifdef __cplusplus
+ extern "C" {
+#endif
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <mLib/bits.h>
+
+#ifndef CATACOMB_GRAND_H
+# include "grand.h"
+#endif
+
+/*----- Data structures ---------------------------------------------------*/
+
+/* --- A secret sharing context --- */
+
+typedef struct gfshare_pt {
+ octet x; /* %$x$%-coordinate of the share */
+ octet *y; /* Pointer to share payload */
+} gfshare_pt;
+
+typedef struct gfshare {
+ unsigned t; /* Threshold */
+ unsigned n; /* The number of shares to make */
+ unsigned i; /* Next free slot in vector */
+ size_t sz; /* Size of the secret and shares */
+ octet *s; /* The secret */
+ gfshare_pt *v; /* Vector of share information */
+} gfshare;
+
+#define GFSHARE_INIT(t, n, sz) { t, n, 0, sz, 0, 0 }
+
+/*----- Functions provided ------------------------------------------------*/
+
+/* --- @gfshare_create@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context to initialize
+ * @unsigned t, n@ = threshold parameters for the system
+ * @size_t sz@ = size of the secret
+ *
+ * Returns: ---
+ *
+ * Use: Initializes a sharing context.
+ */
+
+extern void gfshare_create(gfshare */*s*/, unsigned /*t*/, unsigned /*n*/,
+ size_t /*sz*/);
+
+/* --- @gfshare_destroy@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context to destroy
+ *
+ * Returns: ---
+ *
+ * Use: Disposes of a sharing context. The allocations for the
+ * individual shares and the vector @v@ are freed; the secret is
+ * left alone.
+ */
+
+extern void gfshare_destroy(gfshare */*s*/);
+
+/* --- @gfshare_mkshares@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context to fill in
+ * @grand *r@ = pointer to random number source
+ *
+ * Returns: ---
+ *
+ * Use: Generates @c->n@ secret shares, such that any @c->t@ of them
+ * may be used to recover the secret.
+ *
+ * The context structure is expected to be mostly filled in. In
+ * particular, @t@, @n@, @ssz@ 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.
+ */
+
+extern void gfshare_mkshares(gfshare */*s*/, grand */*r*/);
+
+/* --- @gfshare_add@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to sharing context
+ * @unsigned x@ = which share number this is
+ * @const octet *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 threshold @t@.
+ */
+
+extern unsigned gfshare_add(gfshare */*s*/,
+ unsigned /*x*/, const octet */*y*/);
+
+/* --- @gfshare_combine@ --- *
+ *
+ * Arguments: @gfshare *s@ = pointer to share context
+ * @octet *buf@ = pointer to output buffer for the secret
+ *
+ * Returns: ---
+ *
+ * Use: Reconstructs a secret, given enough shares.
+ */
+
+extern void gfshare_combine(gfshare */*s*/, octet */*buf*/);
+
+/*----- That's all, folks -------------------------------------------------*/
+
+#ifdef __cplusplus
+ }
+#endif
+
+#endif
projects / u / mdw / catacomb / commitdiff