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