secret_sharing.cpp

Voici un exemple de programme permettant d'utiliser le partage de secret (génération des secrets et recomposition de ces derniers) Ce code est générique et permet d'utiliser tous les algorithmes présent dans la librairie. Les éléments fixés ne le sont qu'à titre d'exemple.

/* -----------------------------------------------------------------------
 *
 * Copyright (c) 2002-2005 Mr Ludovic FLAMENT <ludovic.flament@free.fr>, LIEVIN, FRANCE
 *
 * Termes :
 *
 * L'utilisation et/ou la redistribution de ce code (avec ou sans modification),
 * ainsi que de tous les composants du produit (librairies, documentation, exemples, ...)
 * est soumise aux termes de la licence qui vous est attribuée par son auteur.
 *
 * -----------------------------------------------------------------------
 */

#include <stdlib.h>
#include <stdio.h>

#include <include/ecctk-prototype.h>
#include <include/ecctk-ecc.h>

#define MAX_SECRET  5

s2byte secret_sharing()
{
    s2byte  ret     = -1,
            i,
            j;

    /* set output file name
     */
    s1byte  *share_file[MAX_SECRET] = {"share1_file", "share2_file", "share3_file", "share4_file", "share5_file"};

    /* set the secret to share
     */
    u1byte secret[] = "This is my Secret to share";

    /* to get the secret (validation)
     */
    u1byte *result_secret = NULL;

    /* to get the secret size (validation)
     */
    u2byte result_secret_size;

    /* set the number of secret generated and necessary to compute the secret in next time
     */
    u2byte  nb_generated_secret = MAX_SECRET,
            nb_necessary_secret = MAX_SECRET-2;

    /* sharing context
     */
    SHARING_CTX **ctx   = NULL;

    /* creation code
     * ---------------------------------------------------------------------------------------------
     */
    ctx = CreateSecretSharingCtx(secret, sizeof(secret), nb_necessary_secret, nb_generated_secret);
    if (ctx == NULL)
    {
        fprintf(stderr, "Create secret failed\n\n");
        return EXIT_FAILURE;
    }

    /* write all sharing secret value
     * on output file
     */
    for (i = 0; i < nb_generated_secret; i++)
    {
        ret = WriteFileSharingCtx(share_file[i], ctx[i]);
        if (ret != ECCTK_ECC_NO_ERROR)
        {
            fprintf(stderr, "Write sharing secret (Error : %d)\n", ret);
            goto create_end;
        }

        /* free context
         */
        SharingCtxFree(ctx[i]);
        ctx[i] = NULL;
    }

    /* free context
     */
    SharingPtFree(ctx);
    ctx = NULL;

    /* end of creation code
     * ---------------------------------------------------------------------------------------------
     */


    /* verification code
     * check that we can compute the initial secret with only 3 share
     * ---------------------------------------------------------------------------------------------
     */
    ctx = SharingPtInit(nb_necessary_secret);
    if (ctx == NULL)
    {
        fprintf(stderr, "Create pointer context failed\n");
        goto val_end;
    }

    /* read secret in file share1_file, share3_file, share5_file
     */
    for (i = 0, j = 0; i < nb_necessary_secret; i++, j+=2)
    {
        ctx[i] = ReadFileSharingCtx(share_file[j]);
        if (ctx[i] == NULL)
        {
            fprintf(stderr, "Read sharing secret on %s failed\n", share_file[j]);
            goto val_end;
        }
    }

    /* compute the secret value
     */
    result_secret = ResolveSecretSharingCtx(ctx, &result_secret_size);
    if (result_secret == NULL)
    {
        fprintf(stderr, "Error during compute the secret\n");
        goto val_end;
    }

    fprintf(stdout, "Secret (%d) : '%s'\n", result_secret_size, result_secret);

    /* free all context, and result secret
     */
    for (i = 0; i < nb_necessary_secret; i++)
        SharingCtxFree(ctx[i]);
    SharingPtFree(ctx);

    free(result_secret);

    return EXIT_SUCCESS;

    /* end of verification code
     * ---------------------------------------------------------------------------------------------
     */

create_end:

    if (ctx != NULL)
    {
        for (i = 0; i < nb_generated_secret; i++)
            SharingCtxFree(ctx[i]);
        SharingPtFree(ctx);
    }

    return EXIT_FAILURE;

val_end:
    
    if (ctx != NULL)
    {
        for (i = 0; i < nb_necessary_secret; i++)
            SharingCtxFree(ctx[i]);
        SharingPtFree(ctx);
    }

    if (result_secret != NULL)
        free(result_secret);

    return EXIT_FAILURE;
}

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