_ 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 file is part of ASSS (Audit-friendly Shamir's Secret Sharing)
   7  *
   8  * ASSS is free software: you can redistribute it and/or modify
   9  * it under the terms of the GNU Affero General Public License as
  10  * published by the Free Software Foundation, either version 3 of
  11  * the License, or (at your option) any later version.
  12  *
  13  * ASSS is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU Affero General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Affero General Public
  19  * License along with ASSS.  If not, see
  20  * <http://www.gnu.org/licenses/>.
  21  */
  22
  23 #define _GNU_SOURCE
  24
  25 #include <stdio.h>
  26 #include <stdbool.h>
  27 #include <assert.h>
  28 #include <string.h>
  29 #include <sys/mman.h>
  30 #include <unistd.h>
  31 #include <stdlib.h>
  32
  33 #include "shamirssecret.h"
  34
  35 #define MAX_LENGTH 1024
  36 #define ERROREXIT(str...) {fprintf(stderr, str); exit(1);}
  37
  38 #ifndef RAND_SOURCE
  39 #define RAND_SOURCE "/dev/random"
  40 #endif
  41
  42 #ifndef TEST
  43 static void derive_missing_part(uint8_t total_shares, uint8_t shares_required, bool parts_have[], const uint8_t* split_version, const uint8_t* split_x, uint8_t split_index, uint8_t split_size) {
  44         const uint8_t (*D)[split_size] = (const uint8_t (*)[split_size])split_version;
  45         uint8_t x[shares_required], q[shares_required];
  46
  47         // Fill in x/q with the selected shares
  48         uint16_t x_pos = 0;
  49         for (uint8_t i = 0; i < P-1; i++) {
  50                 if (parts_have[i]) {
  51                         x[x_pos] = split_x[i];
  52                         q[x_pos++] = D[i][split_index];
  53                 }
  54         }
  55         assert(x_pos == shares_required - 1);
  56
  57         // Now loop through ALL x we didn't already set (despite not having that many
  58         // shares, because more shares could be added arbitrarily, any x should not be
  59         // able to rule out any possible secrets) and try each possible q, making sure
  60         // that each q gives us a new possibility for the secret.
  61         for (uint16_t final_x = 1; final_x < P; final_x++) {
  62                 bool x_already_used = false;
  63                 for (uint8_t j = 0; j < shares_required; j++) {
  64                         if (x[j] == final_x)
  65                                 x_already_used = true;
  66                 }
  67                 if (x_already_used)
  68                         continue;
  69
  70                 x[shares_required-1] = final_x;
  71                 bool possible_secrets[P];
  72                 memset(possible_secrets, 0, sizeof(possible_secrets));
  73                 for (uint16_t new_q = 0; new_q < P; new_q++) {
  74                         q[shares_required-1] = new_q;
  75                         possible_secrets[calculateSecret(x, q, shares_required)] = 1;
  76                 }
  77
  78                 for (uint16_t i = 0; i < P; i++)
  79                         assert(possible_secrets[i]);
  80         }
  81
  82         //TODO: Check that gcc isn't optimizing this one away
  83         memset(q, 0, sizeof(q));
  84 }
  85
  86 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, const uint8_t* split_version, const uint8_t* x, uint8_t split_index, uint8_t split_size) {
  87         if (parts_included == shares_required-1)
  88                 return derive_missing_part(total_shares, shares_required, parts_have, split_version, x, split_index, split_size);
  89
  90         if (total_shares - progress < shares_required)
  91                 return;
  92
  93         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, parts_included, progress+1, split_version, x, split_index, split_size);
  94         parts_have[progress] = 1;
  95         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, parts_included+1, progress+1, split_version, x, split_index, split_size);
  96         parts_have[progress] = 0;
  97 }
  98
  99 static void check_possible_missing_part_derivations(uint8_t total_shares, uint8_t shares_required, const uint8_t* split_version, const uint8_t* x, uint8_t split_index, uint8_t split_size) {
 100         bool parts_have[P];
 101         memset(parts_have, 0, sizeof(parts_have));
 102         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, 0, 0, split_version, x, split_index, split_size);
 103 }
 104
 105
 106 int main(int argc, char* argv[]) {
 107         assert(mlockall(MCL_CURRENT | MCL_FUTURE) == 0);
 108
 109         char split = 0;
 110         uint8_t total_shares = 0, shares_required = 0;
 111         char* files[P]; uint8_t files_count = 0;
 112         char *in_file = (void*)0, *out_file_param = (void*)0;
 113
 114         int i;
 115         while((i = getopt(argc, argv, "scn:k:f:o:i:h?")) != -1)
 116                 switch(i) {
 117                 case 's':
 118                         if ((split & 0x2) && !(split & 0x1))
 119                                 ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n")
 120                         else
 121                                 split = (0x2 | 0x1);
 122                         break;
 123                 case 'c':
 124                         if ((split & 0x2) && (split & 0x1))
 125                                 ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n")
 126                         else
 127                                 split = 0x2;
 128                         break;
 129                 case 'n': {
 130                         int t = atoi(optarg);
 131                         if (t <= 0 || t >= P)
 132                                 ERROREXIT("n must be > 0 and < %u\n", P)
 133                         else
 134                                 total_shares = t;
 135                         break;
 136                 }
 137                 case 'k': {
 138                         int t = atoi(optarg);
 139                         if (t <= 0 || t >= P)
 140                                 ERROREXIT("n must be > 0 and < %u\n", P)
 141                         else
 142                                 shares_required = t;
 143                         break;
 144                 }
 145                 case 'i':
 146                         in_file = optarg;
 147                         break;
 148                 case 'o':
 149                         out_file_param = optarg;
 150                         break;
 151                 case 'f':
 152                         if (files_count >= P-1)
 153                                 ERROREXIT("May only specify up to %u files\n", P-1)
 154                         files[files_count++] = optarg;
 155                         break;
 156                 case 'h':
 157                 case '?':
 158                         printf("Split usage: -s -n <total shares> -k <shares required> -i <input file> -o <output file path base>\n");
 159                         printf("Combine usage: -c -k <shares provided == shares required> <-f <share>>*k -o <output file>\n");
 160                         exit(0);
 161                         break;
 162                 default:
 163                         ERROREXIT("getopt failed?\n")
 164                 }
 165         if (!(split & 0x2))
 166                 ERROREXIT("Must specify one of -c, -s or -?\n")
 167         split &= 0x1;
 168
 169         if (argc != optind)
 170                 ERROREXIT("Invalid argument\n")
 171
 172         if (split) {
 173                 if (!total_shares || !shares_required)
 174                         ERROREXIT("n and k must be set.\n")
 175
 176                 if (shares_required > total_shares)
 177                         ERROREXIT("k must be <= n\n")
 178
 179                 if (files_count != 0 || !in_file || !out_file_param)
 180                         ERROREXIT("Must specify -i <input file> and -o <output file path base> but not -f in split mode.\n")
 181
 182                 FILE* random = fopen(RAND_SOURCE, "r");
 183                 assert(random);
 184                 FILE* secret_file = fopen(in_file, "r");
 185                 if (!secret_file)
 186                         ERROREXIT("Could not open %s for reading.\n", in_file)
 187
 188                 uint8_t secret[MAX_LENGTH];
 189
 190                 size_t secret_length = fread(secret, 1, MAX_LENGTH*sizeof(uint8_t), secret_file);
 191                 if (secret_length == 0)
 192                         ERROREXIT("Error reading secret\n")
 193                 if (fread(secret, 1, 1, secret_file) > 0)
 194                         ERROREXIT("Secret may not be longer than %u\n", MAX_LENGTH)
 195                 fclose(secret_file);
 196                 printf("Using secret of length %lu\n", secret_length);
 197
 198                 uint8_t a[shares_required], x[total_shares], D[total_shares][secret_length];
 199
 200                 // TODO: The following loop may take a long time and eat lots of /dev/random if total_shares is high
 201                 for (uint32_t i = 0; i < total_shares; i++) {
 202                         int32_t j = -1;
 203                         do {
 204                                 assert(fread(&x[i], sizeof(uint8_t), 1, random) == 1);
 205                                 if (x[i] == 0)
 206                                         continue;
 207                                 for (j = 0; j < i; j++)
 208                                         if (x[j] == x[i])
 209                                                 break;
 210                         } while (j < (int32_t)i); // Inner loop will get to j = i when x[j] != x[i] for all j
 211                         if (i % 32 == 31)
 212                                 printf("Finished picking X coordinates for %u shares\n", i+1);
 213                 }
 214                 for (uint32_t i = 0; i < secret_length; i++) {
 215                         a[0] = secret[i];
 216
 217                         for (uint8_t j = 1; j < shares_required; j++)
 218                                 assert(fread(&a[j], sizeof(uint8_t), 1, random) == 1);
 219                         for (uint8_t j = 0; j < total_shares; j++)
 220                                 D[j][i] = calculateQ(a, shares_required, x[j]);
 221
 222                         // Now, for paranoia's sake, we ensure that no matter which piece we are missing, we can derive no information about the secret
 223                         check_possible_missing_part_derivations(total_shares, shares_required, &(D[0][0]), x, i, secret_length);
 224
 225                         if (i % 32 == 31)
 226                                 printf("Finished processing %u bytes.\n", i+1);
 227                 }
 228
 229                 char out_file_name_buf[strlen(out_file_param) + 4];
 230                 strcpy(out_file_name_buf, out_file_param);
 231                 for (uint8_t i = 0; i < total_shares; i++) {
 232                         sprintf(((char*)out_file_name_buf) + strlen(out_file_param), "%u", i);
 233                         FILE* out_file = fopen(out_file_name_buf, "w+");
 234                         if (!out_file)
 235                                 ERROREXIT("Could not open output file %s\n", out_file_name_buf)
 236
 237                         if (fwrite(&x[i], sizeof(uint8_t), 1, out_file) != 1)
 238                                 ERROREXIT("Could not write 1 byte to %s\n", out_file_name_buf)
 239
 240                         if (fwrite(D[i], 1, secret_length, out_file) != secret_length)
 241                                 ERROREXIT("Could not write %lu bytes to %s\n", secret_length, out_file_name_buf)
 242
 243                         fclose(out_file);
 244                 }
 245
 246                 // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out)
 247                 memset(secret, 0, sizeof(uint8_t)*secret_length);
 248                 memset(a, 0, sizeof(uint8_t)*shares_required);
 249                 memset(x, 0, sizeof(uint8_t)*total_shares);
 250                 memset(in_file, 0, strlen(in_file));
 251
 252                 fclose(random);
 253         } else {
 254                 if (!shares_required)
 255                         ERROREXIT("k must be set.\n")
 256
 257                 if (files_count != shares_required || in_file || !out_file_param)
 258                         ERROREXIT("Must not specify -i and must specify -o and exactly k -f <input file>s in combine mode.\n")
 259
 260                 uint8_t x[shares_required], q[shares_required];
 261                 FILE* files_fps[shares_required];
 262
 263                 for (uint8_t i = 0; i < shares_required; i++) {
 264                         files_fps[i] = fopen(files[i], "r");
 265                         if (!files_fps[i])
 266                                 ERROREXIT("Couldn't open file %s for reading.\n", files[i])
 267                         if (fread(&x[i], sizeof(uint8_t), 1, files_fps[i]) != 1)
 268                                 ERROREXIT("Couldn't read the x byte of %s\n", files[i])
 269                 }
 270
 271                 uint8_t secret[MAX_LENGTH];
 272
 273                 uint32_t i = 0;
 274                 while (fread(&q[0], sizeof(uint8_t), 1, files_fps[0]) == 1) {
 275                         for (uint8_t j = 1; j < shares_required; j++) {
 276                                 if (fread(&q[j], sizeof(uint8_t), 1, files_fps[j]) != 1)
 277                                         ERROREXIT("Couldn't read next byte from %s\n", files[j])
 278                         }
 279                         secret[i++] = calculateSecret(x, q, shares_required);
 280                 }
 281                 printf("Got secret of length %u\n", i);
 282
 283                 FILE* out_file = fopen(out_file_param, "w+");
 284                 fwrite(secret, sizeof(uint8_t), i, out_file);
 285                 fclose(out_file);
 286
 287                 for (uint8_t i = 0; i < shares_required; i++)
 288                         fclose(files_fps[i]);
 289
 290                 // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out)
 291                 memset(secret, 0, sizeof(uint8_t)*i);
 292                 memset(q, 0, sizeof(uint8_t)*shares_required);
 293                 memset(out_file_param, 0, strlen(out_file_param));
 294                 for (uint8_t i = 0; i < shares_required; i++)
 295                         memset(files[i], 0, strlen(files[i]));
 296                 memset(x, 0, sizeof(uint8_t)*shares_required);
 297         }
 298
 299         return 0;
 300 }
 301 #endif // !defined(TEST)