_ Git - shamirs/blob - main.c

   1 /*
   2  * Shamir's secret sharing CLI interface
   3  *
   4  * Copyright (C) 2013 Matt Corallo <git@bluematt.me>
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms and conditions of the GNU General Public License,
   8  * version 2, as published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  13  * more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along with
  16  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
  17  * Place - Suite 330, Boston, MA 02111-1307 USA.
  18  */
  19
  20 #define _GNU_SOURCE
  21
  22 #include <stdio.h>
  23 #include <stdbool.h>
  24 #include <assert.h>
  25 #include <string.h>
  26 #include <sys/mman.h>
  27 #include <unistd.h>
  28 #include <stdlib.h>
  29
  30 #include "shamirssecret.h"
  31
  32 #define MAX_LENGTH 1024
  33 #define ERROREXIT(str...) {fprintf(stderr, str); exit(1);}
  34
  35 #ifndef TEST
  36 static void derive_missing_part(uint8_t total_shares, uint8_t shares_required, bool parts_have[], uint8_t* split_version, uint8_t split_index, uint8_t split_size) {
  37         uint8_t (*D)[split_size] = (uint8_t (*)[split_size])split_version;
  38         uint8_t x[shares_required], q[shares_required];
  39
  40         // Fill in x/q with the selected shares
  41         uint16_t x_pos = 0;
  42         for (uint8_t i = 0; i < P-1; i++) {
  43                 if (parts_have[i]) {
  44                         x[x_pos] = i+1;
  45                         q[x_pos++] = D[i][split_index];
  46                 }
  47         }
  48         assert(x_pos == shares_required - 1);
  49
  50         // Now loop through ALL x we didn't already set (despite not having that many
  51         // shares, because more shares could be added arbitrarily, any x should not be
  52         // able to rule out any possible secrets) and try each possible q, making sure
  53         // that each q gives us a new possibility for the secret.
  54         bool impossible_secrets[P];
  55         memset(impossible_secrets, 0, sizeof(impossible_secrets));
  56         for (uint16_t final_x = 1; final_x < P; final_x++) {
  57                 bool x_already_used = false;
  58                 for (uint8_t j = 0; j < shares_required; j++) {
  59                         if (x[j] == final_x)
  60                                 x_already_used = true;
  61                 }
  62                 if (x_already_used)
  63                         continue;
  64
  65                 x[shares_required-1] = final_x;
  66                 bool possible_secrets[P];
  67                 memset(possible_secrets, 0, sizeof(possible_secrets));
  68                 for (uint16_t new_q = 0; new_q < P; new_q++) {
  69                         q[shares_required-1] = new_q;
  70                         possible_secrets[calculateSecret(x, q, shares_required)] = 1;
  71                 }
  72
  73                 for (uint16_t i = 0; i < P; i++)
  74                         assert(possible_secrets[i]);
  75         }
  76
  77         //TODO: Check that gcc isn't optimizing this one away
  78         memset(q, 0, sizeof(q));
  79 }
  80
  81 static void check_possible_missing_part_derivations_intern(uint8_t total_shares, uint8_t shares_required, bool parts_have[], uint8_t parts_included, uint16_t progress, uint8_t* split_version, uint8_t split_index, uint8_t split_size) {
  82         if (parts_included == shares_required-1)
  83                 return derive_missing_part(total_shares, shares_required, parts_have, split_version, split_index, split_size);
  84
  85         if (total_shares - progress < shares_required)
  86                 return;
  87
  88         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, parts_included, progress+1, split_version, split_index, split_size);
  89         parts_have[progress] = 1;
  90         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, parts_included+1, progress+1, split_version, split_index, split_size);
  91         parts_have[progress] = 0;
  92 }
  93
  94 static void check_possible_missing_part_derivations(uint8_t total_shares, uint8_t shares_required, uint8_t* split_version, uint8_t split_index, uint8_t split_size) {
  95         bool parts_have[P];
  96         memset(parts_have, 0, sizeof(parts_have));
  97         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, 0, 0, split_version, split_index, split_size);
  98 }
  99
 100
 101 int main(int argc, char* argv[]) {
 102         assert(mlockall(MCL_CURRENT | MCL_FUTURE) == 0);
 103
 104         char split = 0;
 105         uint8_t total_shares = 0, shares_required = 0;
 106         char* files[P]; uint8_t files_count = 0;
 107         char *in_file = (void*)0, *out_file_param = (void*)0;
 108
 109         int i;
 110         while((i = getopt(argc, argv, "scn:k:f:o:i:h?")) != -1)
 111                 switch(i) {
 112                 case 's':
 113                         if ((split & 0x2) && !(split & 0x1))
 114                                 ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n")
 115                         else
 116                                 split = (0x2 | 0x1);
 117                         break;
 118                 case 'c':
 119                         if ((split & 0x2) && (split & 0x1))
 120                                 ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n")
 121                         else
 122                                 split = 0x2;
 123                         break;
 124                 case 'n': {
 125                         int t = atoi(optarg);
 126                         if (t <= 0 || t >= P)
 127                                 ERROREXIT("n must be > 0 and < %u\n", P)
 128                         else
 129                                 total_shares = t;
 130                         break;
 131                 }
 132                 case 'k': {
 133                         int t = atoi(optarg);
 134                         if (t <= 0 || t >= P)
 135                                 ERROREXIT("n must be > 0 and < %u\n", P)
 136                         else
 137                                 shares_required = t;
 138                         break;
 139                 }
 140                 case 'i':
 141                         in_file = optarg;
 142                         break;
 143                 case 'o':
 144                         out_file_param = optarg;
 145                         break;
 146                 case 'f':
 147                         if (files_count >= P-1)
 148                                 ERROREXIT("May only specify up to %u files\n", P-1)
 149                         files[files_count++] = optarg;
 150                         break;
 151                 case 'h':
 152                 case '?':
 153                         printf("Split usage: -s -n <total shares> -k <shares required> -i <input file> -o <output file path base>\n");
 154                         printf("Combine usage: -c -k <shares provided == shares required> <-f <share>>*k -o <output file>\n");
 155                         exit(0);
 156                         break;
 157                 default:
 158                         ERROREXIT("getopt failed?\n")
 159                 }
 160         if (!(split & 0x2))
 161                 ERROREXIT("Must specify one of -c, -s or -?\n")
 162         split &= 0x1;
 163
 164         if (argc != optind)
 165                 ERROREXIT("Invalid argument\n")
 166
 167         if (split) {
 168                 if (!total_shares || !shares_required)
 169                         ERROREXIT("n and k must be set.\n")
 170
 171                 if (shares_required > total_shares)
 172                         ERROREXIT("k must be <= n\n")
 173
 174                 if (files_count != 0 || !in_file || !out_file_param)
 175                         ERROREXIT("Must specify -i <input file> and -o <output file path base> but not -f in split mode.\n")
 176
 177                 FILE* random = fopen("/dev/random", "r");
 178                 assert(random);
 179                 FILE* secret_file = fopen(in_file, "r");
 180                 if (!secret_file)
 181                         ERROREXIT("Could not open %s for reading.\n", in_file)
 182
 183                 uint8_t secret[MAX_LENGTH];
 184
 185                 size_t secret_length = fread(secret, 1, MAX_LENGTH*sizeof(uint8_t), secret_file);
 186                 if (secret_length == 0)
 187                         ERROREXIT("Error reading secret\n")
 188                 if (fread(secret, 1, 1, secret_file) > 0)
 189                         ERROREXIT("Secret may not be longer than %u\n", MAX_LENGTH)
 190                 fclose(secret_file);
 191                 printf("Using secret of length %lu\n", secret_length);
 192
 193                 uint8_t a[shares_required], D[total_shares][secret_length];
 194
 195                 for (uint32_t i = 0; i < secret_length; i++) {
 196                         a[0] = secret[i];
 197
 198                         for (uint8_t j = 1; j < shares_required; j++)
 199                                 assert(fread(&a[j], sizeof(uint8_t), 1, random) == 1);
 200                         for (uint8_t j = 0; j < total_shares; j++)
 201                                 D[j][i] = calculateQ(a, shares_required, j+1);
 202
 203                         // Now, for paranoia's sake, we ensure that no matter which piece we are missing, we can derive no information about the secret
 204                         check_possible_missing_part_derivations(total_shares, shares_required, &(D[0][0]), i, secret_length);
 205
 206                         if (i % 32 == 0 && i != 0)
 207                                 printf("Finished processing %u bytes.\n", i);
 208                 }
 209
 210                 char out_file_name_buf[strlen(out_file_param) + 4];
 211                 strcpy(out_file_name_buf, out_file_param);
 212                 for (uint8_t i = 0; i < total_shares; i++) {
 213                         /*printf("%u-", i);
 214                         for (uint8_t j = 0; j < secret_length; j++)
 215                                 printf("%02x", D[i][j]);
 216                         printf("\n");*/
 217
 218                         sprintf(((char*)out_file_name_buf) + strlen(out_file_param), "%u", i);
 219                         FILE* out_file = fopen(out_file_name_buf, "w+");
 220                         if (!out_file)
 221                                 ERROREXIT("Could not open output file %s\n", out_file_name_buf)
 222
 223                         uint8_t x = i+1;
 224                         if (fwrite(&x, sizeof(uint8_t), 1, out_file) != 1)
 225                                 ERROREXIT("Could not write 1 byte to %s\n", out_file_name_buf)
 226
 227                         if (fwrite(D[i], 1, secret_length, out_file) != secret_length)
 228                                 ERROREXIT("Could not write %lu bytes to %s\n", secret_length, out_file_name_buf)
 229
 230                         fclose(out_file);
 231                 }
 232                 /*printf("secret = ");
 233                 for (uint8_t i = 0; i < secret_length; i++)
 234                         printf("%02x", secret[i]);
 235                 printf("\n");*/
 236
 237                 // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out)
 238                 memset(secret, 0, sizeof(uint8_t)*secret_length);
 239                 memset(a, 0, sizeof(uint8_t)*shares_required);
 240                 memset(in_file, 0, strlen(in_file));
 241
 242                 fclose(random);
 243         } else {
 244                 if (!shares_required)
 245                         ERROREXIT("k must be set.\n")
 246
 247                 if (files_count != shares_required || in_file || !out_file_param)
 248                         ERROREXIT("Must not specify -i and must specify -o and exactly k -f <input file>s in combine mode.\n")
 249
 250                 uint8_t x[shares_required], q[shares_required];
 251                 FILE* files_fps[shares_required];
 252
 253                 for (uint8_t i = 0; i < shares_required; i++) {
 254                         files_fps[i] = fopen(files[i], "r");
 255                         if (!files_fps[i])
 256                                 ERROREXIT("Couldn't open file %s for reading.\n", files[i])
 257                         if (fread(&x[i], sizeof(uint8_t), 1, files_fps[i]) != 1)
 258                                 ERROREXIT("Couldn't read the x byte of %s\n", files[i])
 259                 }
 260
 261                 uint8_t secret[MAX_LENGTH];
 262
 263                 uint32_t i = 0;
 264                 while (fread(&q[0], sizeof(uint8_t), 1, files_fps[0]) == 1) {
 265                         for (uint8_t j = 1; j < shares_required; j++) {
 266                                 if (fread(&q[j], sizeof(uint8_t), 1, files_fps[j]) != 1)
 267                                         ERROREXIT("Couldn't read next byte from %s\n", files[j])
 268                         }
 269                         secret[i++] = calculateSecret(x, q, shares_required);
 270                 }
 271                 printf("Got secret of length %u\n", i);
 272
 273                 FILE* out_file = fopen(out_file_param, "w+");
 274                 fwrite(secret, sizeof(uint8_t), i, out_file);
 275                 fclose(out_file);
 276
 277                 for (uint8_t i = 0; i < shares_required; i++)
 278                         fclose(files_fps[i]);
 279
 280                 // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out)
 281                 memset(secret, 0, sizeof(uint8_t)*i);
 282                 memset(q, 0, sizeof(uint8_t)*shares_required);
 283                 memset(out_file_param, 0, strlen(out_file_param));
 284                 for (uint8_t i = 0; i < shares_required; i++)
 285                         memset(files[i], 0, strlen(files[i]));
 286                 memset(x, 0, sizeof(uint8_t)*shares_required);
 287         }
 288
 289         return 0;
 290 }
 291 #endif // !defined(TEST)