_ 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         bool impossible_secrets[P];
  62         memset(impossible_secrets, 0, sizeof(impossible_secrets));
  63         for (uint16_t final_x = 1; final_x < P; final_x++) {
  64                 bool x_already_used = false;
  65                 for (uint8_t j = 0; j < shares_required; j++) {
  66                         if (x[j] == final_x)
  67                                 x_already_used = true;
  68                 }
  69                 if (x_already_used)
  70                         continue;
  71
  72                 x[shares_required-1] = final_x;
  73                 bool possible_secrets[P];
  74                 memset(possible_secrets, 0, sizeof(possible_secrets));
  75                 for (uint16_t new_q = 0; new_q < P; new_q++) {
  76                         q[shares_required-1] = new_q;
  77                         possible_secrets[calculateSecret(x, q, shares_required)] = 1;
  78                 }
  79
  80                 for (uint16_t i = 0; i < P; i++)
  81                         assert(possible_secrets[i]);
  82         }
  83
  84         //TODO: Check that gcc isn't optimizing this one away
  85         memset(q, 0, sizeof(q));
  86 }
  87
  88 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) {
  89         if (parts_included == shares_required-1)
  90                 return derive_missing_part(total_shares, shares_required, parts_have, split_version, x, split_index, split_size);
  91
  92         if (total_shares - progress < shares_required)
  93                 return;
  94
  95         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, parts_included, progress+1, split_version, x, split_index, split_size);
  96         parts_have[progress] = 1;
  97         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, parts_included+1, progress+1, split_version, x, split_index, split_size);
  98         parts_have[progress] = 0;
  99 }
 100
 101 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) {
 102         bool parts_have[P];
 103         memset(parts_have, 0, sizeof(parts_have));
 104         check_possible_missing_part_derivations_intern(total_shares, shares_required, parts_have, 0, 0, split_version, x, split_index, split_size);
 105 }
 106
 107
 108 int main(int argc, char* argv[]) {
 109         assert(mlockall(MCL_CURRENT | MCL_FUTURE) == 0);
 110
 111         char split = 0;
 112         uint8_t total_shares = 0, shares_required = 0;
 113         char* files[P]; uint8_t files_count = 0;
 114         char *in_file = (void*)0, *out_file_param = (void*)0;
 115
 116         int i;
 117         while((i = getopt(argc, argv, "scn:k:f:o:i:h?")) != -1)
 118                 switch(i) {
 119                 case 's':
 120                         if ((split & 0x2) && !(split & 0x1))
 121                                 ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n")
 122                         else
 123                                 split = (0x2 | 0x1);
 124                         break;
 125                 case 'c':
 126                         if ((split & 0x2) && (split & 0x1))
 127                                 ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n")
 128                         else
 129                                 split = 0x2;
 130                         break;
 131                 case 'n': {
 132                         int t = atoi(optarg);
 133                         if (t <= 0 || t >= P)
 134                                 ERROREXIT("n must be > 0 and < %u\n", P)
 135                         else
 136                                 total_shares = t;
 137                         break;
 138                 }
 139                 case 'k': {
 140                         int t = atoi(optarg);
 141                         if (t <= 0 || t >= P)
 142                                 ERROREXIT("n must be > 0 and < %u\n", P)
 143                         else
 144                                 shares_required = t;
 145                         break;
 146                 }
 147                 case 'i':
 148                         in_file = optarg;
 149                         break;
 150                 case 'o':
 151                         out_file_param = optarg;
 152                         break;
 153                 case 'f':
 154                         if (files_count >= P-1)
 155                                 ERROREXIT("May only specify up to %u files\n", P-1)
 156                         files[files_count++] = optarg;
 157                         break;
 158                 case 'h':
 159                 case '?':
 160                         printf("Split usage: -s -n <total shares> -k <shares required> -i <input file> -o <output file path base>\n");
 161                         printf("Combine usage: -c -k <shares provided == shares required> <-f <share>>*k -o <output file>\n");
 162                         exit(0);
 163                         break;
 164                 default:
 165                         ERROREXIT("getopt failed?\n")
 166                 }
 167         if (!(split & 0x2))
 168                 ERROREXIT("Must specify one of -c, -s or -?\n")
 169         split &= 0x1;
 170
 171         if (argc != optind)
 172                 ERROREXIT("Invalid argument\n")
 173
 174         if (split) {
 175                 if (!total_shares || !shares_required)
 176                         ERROREXIT("n and k must be set.\n")
 177
 178                 if (shares_required > total_shares)
 179                         ERROREXIT("k must be <= n\n")
 180
 181                 if (files_count != 0 || !in_file || !out_file_param)
 182                         ERROREXIT("Must specify -i <input file> and -o <output file path base> but not -f in split mode.\n")
 183
 184                 FILE* random = fopen(RAND_SOURCE, "r");
 185                 assert(random);
 186                 FILE* secret_file = fopen(in_file, "r");
 187                 if (!secret_file)
 188                         ERROREXIT("Could not open %s for reading.\n", in_file)
 189
 190                 uint8_t secret[MAX_LENGTH];
 191
 192                 size_t secret_length = fread(secret, 1, MAX_LENGTH*sizeof(uint8_t), secret_file);
 193                 if (secret_length == 0)
 194                         ERROREXIT("Error reading secret\n")
 195                 if (fread(secret, 1, 1, secret_file) > 0)
 196                         ERROREXIT("Secret may not be longer than %u\n", MAX_LENGTH)
 197                 fclose(secret_file);
 198                 printf("Using secret of length %lu\n", secret_length);
 199
 200                 uint8_t a[shares_required], x[total_shares], D[total_shares][secret_length];
 201
 202                 // TODO: The following loop may take a long time and eat lots of /dev/random if total_shares is high
 203                 for (uint32_t i = 0; i < total_shares; i++) {
 204                         int32_t j = 0;
 205                         do {
 206                                 assert(fread(&x[i], sizeof(uint8_t), 1, random) == 1);
 207                                 if (x[i] == 0)
 208                                         continue;
 209                                 for (j = 0; j < i; j++)
 210                                         if (x[j] == x[i])
 211                                                 break;
 212                         } while (j < i); // Inner loop will get to j = i when x[j] != x[i] for all j
 213                         if (i % 32 == 31)
 214                                 printf("Finished picking X coordinates for %u shares\n", i+1);
 215                 }
 216                 for (uint32_t i = 0; i < secret_length; i++) {
 217                         a[0] = secret[i];
 218
 219                         for (uint8_t j = 1; j < shares_required; j++)
 220                                 assert(fread(&a[j], sizeof(uint8_t), 1, random) == 1);
 221                         for (uint8_t j = 0; j < total_shares; j++)
 222                                 D[j][i] = calculateQ(a, shares_required, x[j]);
 223
 224                         // Now, for paranoia's sake, we ensure that no matter which piece we are missing, we can derive no information about the secret
 225                         check_possible_missing_part_derivations(total_shares, shares_required, &(D[0][0]), x, i, secret_length);
 226
 227                         if (i % 32 == 31)
 228                                 printf("Finished processing %u bytes.\n", i+1);
 229                 }
 230
 231                 char out_file_name_buf[strlen(out_file_param) + 4];
 232                 strcpy(out_file_name_buf, out_file_param);
 233                 for (uint8_t i = 0; i < total_shares; i++) {
 234                         sprintf(((char*)out_file_name_buf) + strlen(out_file_param), "%u", i);
 235                         FILE* out_file = fopen(out_file_name_buf, "w+");
 236                         if (!out_file)
 237                                 ERROREXIT("Could not open output file %s\n", out_file_name_buf)
 238
 239                         if (fwrite(&x[i], sizeof(uint8_t), 1, out_file) != 1)
 240                                 ERROREXIT("Could not write 1 byte to %s\n", out_file_name_buf)
 241
 242                         if (fwrite(D[i], 1, secret_length, out_file) != secret_length)
 243                                 ERROREXIT("Could not write %lu bytes to %s\n", secret_length, out_file_name_buf)
 244
 245                         fclose(out_file);
 246                 }
 247
 248                 // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out)
 249                 memset(secret, 0, sizeof(uint8_t)*secret_length);
 250                 memset(a, 0, sizeof(uint8_t)*shares_required);
 251                 memset(x, 0, sizeof(uint8_t)*total_shares);
 252                 memset(in_file, 0, strlen(in_file));
 253
 254                 fclose(random);
 255         } else {
 256                 if (!shares_required)
 257                         ERROREXIT("k must be set.\n")
 258
 259                 if (files_count != shares_required || in_file || !out_file_param)
 260                         ERROREXIT("Must not specify -i and must specify -o and exactly k -f <input file>s in combine mode.\n")
 261
 262                 uint8_t x[shares_required], q[shares_required];
 263                 FILE* files_fps[shares_required];
 264
 265                 for (uint8_t i = 0; i < shares_required; i++) {
 266                         files_fps[i] = fopen(files[i], "r");
 267                         if (!files_fps[i])
 268                                 ERROREXIT("Couldn't open file %s for reading.\n", files[i])
 269                         if (fread(&x[i], sizeof(uint8_t), 1, files_fps[i]) != 1)
 270                                 ERROREXIT("Couldn't read the x byte of %s\n", files[i])
 271                 }
 272
 273                 uint8_t secret[MAX_LENGTH];
 274
 275                 uint32_t i = 0;
 276                 while (fread(&q[0], sizeof(uint8_t), 1, files_fps[0]) == 1) {
 277                         for (uint8_t j = 1; j < shares_required; j++) {
 278                                 if (fread(&q[j], sizeof(uint8_t), 1, files_fps[j]) != 1)
 279                                         ERROREXIT("Couldn't read next byte from %s\n", files[j])
 280                         }
 281                         secret[i++] = calculateSecret(x, q, shares_required);
 282                 }
 283                 printf("Got secret of length %u\n", i);
 284
 285                 FILE* out_file = fopen(out_file_param, "w+");
 286                 fwrite(secret, sizeof(uint8_t), i, out_file);
 287                 fclose(out_file);
 288
 289                 for (uint8_t i = 0; i < shares_required; i++)
 290                         fclose(files_fps[i]);
 291
 292                 // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out)
 293                 memset(secret, 0, sizeof(uint8_t)*i);
 294                 memset(q, 0, sizeof(uint8_t)*shares_required);
 295                 memset(out_file_param, 0, strlen(out_file_param));
 296                 for (uint8_t i = 0; i < shares_required; i++)
 297                         memset(files[i], 0, strlen(files[i]));
 298                 memset(x, 0, sizeof(uint8_t)*shares_required);
 299         }
 300
 301         return 0;
 302 }
 303 #endif // !defined(TEST)