+++ /dev/null
-/* -*-c-*-
- *
- * $Id$
- *
- * 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.
- */
-
-/*----- Notes on the system -----------------------------------------------*
- *
- * This uses a variant of Shamir's secret sharing system. Shamir's original
- * system used polynomials modulo a large prime. This implementation instead
- * uses the field %$\gf{2^8}$%, represented by
- *
- * %$\gf{2}[x]/(x^8 + x^4 + x^3 + x^2 + 1)$%
- *
- * and shares each byte of the secret independently. It is therefore limited
- * to 255 players, although this probably isn't a serious limitation in
- * practice.
- *
- * Share creation and reconstruction is extremely efficient. Contrast the
- * performance of the straightforward implementation based on multiprecision
- * arithmetic.
- */
-
-#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 {
- unsigned t; /* Threshold */
- unsigned i; /* Next free slot in vector */
- size_t sz; /* Size of the secret and shares */
- octet *v; /* Vector of share information */
-} gfshare;
-
-#define GFSHARE_INIT(t, sz) { t, 0, sz, 0 }
-
-#define GFSHARE_INDEX(s, i) ((s)->v[(i) * ((s)->sz + 1)])
-
-/*----- Functions provided ------------------------------------------------*/
-
-/* --- @gfshare_create@ --- *
- *
- * Arguments: @gfshare *s@ = pointer to share context to initialize
- * @unsigned t@ = threshold for the system
- * @size_t sz@ = size of the secret
- *
- * Returns: ---
- *
- * Use: Initializes a sharing context.
- */
-
-extern void gfshare_create(gfshare */*s*/, unsigned /*t*/, 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
- * @const void *buf@ = pointer to 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 @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*/,
- const void */*buf*/);
-
-/* --- @gfshare_get@ --- *
- *
- * Arguments: @gfshare *s@ = pointer to share conext
- * @unsigned x@ = share index to fetch
- * @void *buf@ = pointer to output buffer
- *
- * Returns: ---
- *
- * Use: Extracts a share from the system. You may extract up to 255
- * shares from the system. Shares are indexed from 0.
- */
-
-extern void gfshare_get(gfshare */*s*/, unsigned /*x*/, void */*buf*/);
-
-/* --- @gfshare_addedp@ --- *
- *
- * Arguments: @gfshare *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.
- */
-
-extern int gfshare_addedp(gfshare */*s*/, unsigned /*x*/);
-
-/* --- @gfshare_add@ --- *
- *
- * Arguments: @gfshare *s@ = pointer to sharing context
- * @unsigned x@ = which share number this is
- * @const void *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 void */*y*/);
-
-/* --- @gfshare_combine@ --- *
- *
- * Arguments: @gfshare *s@ = pointer to share context
- * @void *buf@ = pointer to output buffer for the secret
- *
- * Returns: ---
- *
- * Use: Reconstructs a secret, given enough shares.
- */
-
-extern void gfshare_combine(gfshare */*s*/, void */*buf*/);
-
-/*----- That's all, folks -------------------------------------------------*/
-
-#ifdef __cplusplus
- }
-#endif
-
-#endif
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