X-Git-Url: http://git.bitcoin.ninja/index.cgi?p=shamirs;a=blobdiff_plain;f=shamirssecret.c;h=2d6e7aac0c9a77bc41d9fc12465fd400bf82a2e6;hp=80f835c46318bb2ab825a40135af853d51b96821;hb=f76ba5528394212f4b95427c3aaac9a91a8acb1e;hpb=1be5bb401e6c909e5856d3a7340963cf132b06ed diff --git a/shamirssecret.c b/shamirssecret.c index 80f835c..2d6e7aa 100644 --- a/shamirssecret.c +++ b/shamirssecret.c @@ -1,21 +1,39 @@ -#define _GNU_SOURCE +/* + * Shamir's secret sharing sharing implementation + * + * Copyright (C) 2013 Matt Corallo + * + * This program is free software; you can redistribute it and/or modify it + * under the terms and conditions of the GNU General Public License, + * version 2, as published by the Free Software Foundation. + * + * This program is distributed in the hope it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for + * more details. + * + * You should have received a copy of the GNU General Public License along with + * this program; if not, write to the Free Software Foundation, Inc., 59 Temple + * Place - Suite 330, Boston, MA 02111-1307 USA. + */ #include -#include + +#ifndef IN_KERNEL #include -#include -#include -#include -#include +#define CHECKSTATE(x) assert(x) +#else +#include +#define CHECKSTATE(x) BUG_ON(x) +#endif -#define MAX_LENGTH 1024 -#define ERROREXIT(str...) {fprintf(stderr, str); exit(1);} +#include "shamirssecret.h" /* * Calculations across the finite field GF(2^8) */ -#define P 256 +#ifndef TEST static uint8_t field_add(uint8_t a, uint8_t b) { return a ^ b; } @@ -27,7 +45,11 @@ static uint8_t field_sub(uint8_t a, uint8_t b) { static uint8_t field_neg(uint8_t a) { return field_sub(0, a); } +#endif +//TODO: Using static tables will very likely create side-channel attacks when measuring cache hits +// Because these are fairly small tables, we can probably get them loaded mostly/fully into +// cache before use to break such attacks. static const uint8_t exp[P] = { 0x01, 0x03, 0x05, 0x0f, 0x11, 0x33, 0x55, 0xff, 0x1a, 0x2e, 0x72, 0x96, 0xa1, 0xf8, 0x13, 0x35, 0x5f, 0xe1, 0x38, 0x48, 0xd8, 0x73, 0x95, 0xa4, 0xf7, 0x02, 0x06, 0x0a, 0x1e, 0x22, 0x66, 0xaa, @@ -83,7 +105,7 @@ static uint8_t field_mul(uint8_t a, uint8_t b) { } static uint8_t field_invert(uint8_t a) { - assert(a != 0); + CHECKSTATE(a != 0); return exp[0xff - log[a]]; // log[1] == 0xff } @@ -105,7 +127,7 @@ static uint8_t field_pow(uint8_t a, uint8_t e) { #ifndef TEST // Although this function works for a==0, its not trivially obvious why, // and since we never call with a==0, we just assert a != 0 (except when testing) - assert(a != 0); + CHECKSTATE(a != 0); #endif return field_pow_ret(exp[(log[a] * e) % 255], a, e); } @@ -136,18 +158,18 @@ static uint8_t field_pow_calc(uint8_t a, uint8_t e) { int main() { // Test inversion with the logarithm tables for (uint16_t i = 1; i < P; i++) - assert(field_mul_calc(i, field_invert(i)) == 1); + CHECKSTATE(field_mul_calc(i, field_invert(i)) == 1); // Test multiplication with the logarithm tables for (uint16_t i = 0; i < P; i++) { for (uint16_t j = 0; j < P; j++) - assert(field_mul(i, j) == field_mul_calc(i, j)); + CHECKSTATE(field_mul(i, j) == field_mul_calc(i, j)); } // Test exponentiation with the logarithm tables for (uint16_t i = 0; i < P; i++) { for (uint16_t j = 0; j < P; j++) - assert(field_pow(i, j) == field_pow_calc(i, j)); + CHECKSTATE(field_pow(i, j) == field_pow_calc(i, j)); } } #endif // defined(TEST) @@ -158,22 +180,29 @@ int main() { * Calculations across the polynomial q */ #ifndef TEST -static uint8_t calculateQ(uint8_t a[], uint8_t k, uint8_t x) { - assert(x != 0); // q(0) == secret, though so does a[0] - uint8_t ret = a[0]; - for (uint8_t i = 1; i < k; i++) { - ret = field_add(ret, field_mul(a[i], field_pow(x, i))); +/** + * Calculates the Y coordinate that the point with the given X + * coefficients[0] == secret, the rest are random values + */ +uint8_t calculateQ(uint8_t coefficients[], uint8_t shares_required, uint8_t x) { + CHECKSTATE(x != 0); // q(0) == secret, though so does a[0] + uint8_t ret = coefficients[0]; + for (uint8_t i = 1; i < shares_required; i++) { + ret = field_add(ret, field_mul(coefficients[i], field_pow(x, i))); } return ret; } -uint8_t calculateSecret(uint8_t x[], uint8_t q[], uint8_t k) { +/** + * Derives the secret given a set of shares_required points (x and q coordinates) + */ +uint8_t calculateSecret(uint8_t x[], uint8_t q[], uint8_t shares_required) { // Calculate the x^0 term using a derivation of the forumula at // http://en.wikipedia.org/wiki/Lagrange_polynomial#Example_2 uint8_t ret = 0; - for (uint8_t i = 0; i < k; i++) { + for (uint8_t i = 0; i < shares_required; i++) { uint8_t temp = q[i]; - for (uint8_t j = 0; j < k; j++) { + for (uint8_t j = 0; j < shares_required; j++) { if (i == j) continue; temp = field_mul(temp, field_neg(x[j])); @@ -183,194 +212,4 @@ uint8_t calculateSecret(uint8_t x[], uint8_t q[], uint8_t k) { } return ret; } - - - -int main(int argc, char* argv[]) { - assert(mlockall(MCL_CURRENT | MCL_FUTURE) == 0); - - char split = 0; - uint8_t total_shares = 0, shares_required = 0; - char* files[P]; uint8_t files_count = 0; - char *in_file = (void*)0, *out_file_param = (void*)0; - - int i; - while((i = getopt(argc, argv, "scn:k:f:o:i:h?")) != -1) - switch(i) { - case 's': - if ((split & 0x2) && !(split & 0x1)) - ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n") - else - split = (0x2 | 0x1); - break; - case 'c': - if ((split & 0x2) && (split & 0x1)) - ERROREXIT("-s (split) and -c (combine) are mutually exclusive\n") - else - split = 0x2; - break; - case 'n': { - int t = atoi(optarg); - if (t <= 0 || t >= P) - ERROREXIT("n must be > 0 and < %u\n", P) - else - total_shares = t; - break; - } - case 'k': { - int t = atoi(optarg); - if (t <= 0 || t >= P) - ERROREXIT("n must be > 0 and < %u\n", P) - else - shares_required = t; - break; - } - case 'i': - in_file = optarg; - break; - case 'o': - out_file_param = optarg; - break; - case 'f': - if (files_count >= P-1) - ERROREXIT("May only specify up to %u files\n", P-1) - files[files_count++] = optarg; - break; - case 'h': - case '?': - printf("Split usage: -s -n -k -i -o \n"); - printf("Combine usage: -c -k <-f >*k -o \n"); - exit(0); - break; - default: - ERROREXIT("getopt failed?\n") - } - if (!(split & 0x2)) - ERROREXIT("Must specify one of -c, -s or -?\n") - split &= 0x1; - - if (argc != optind) - ERROREXIT("Invalid argument\n") - - if (split) { - if (!total_shares || !shares_required) - ERROREXIT("n and k must be set.\n") - - if (shares_required > total_shares) - ERROREXIT("k must be <= n\n") - - if (files_count != 0 || !in_file || !out_file_param) - ERROREXIT("Must specify -i and -o but not -f in split mode.\n") - - FILE* random = fopen("/dev/random", "r"); - assert(random); - FILE* secret_file = fopen(in_file, "r"); - if (!secret_file) - ERROREXIT("Could not open %s for reading.\n", in_file) - - uint8_t secret[MAX_LENGTH]; - - size_t secret_length = fread(secret, 1, MAX_LENGTH*sizeof(uint8_t), secret_file); - if (secret_length == 0) - ERROREXIT("Error reading secret\n") - if (fread(secret, 1, 1, secret_file) > 0) - ERROREXIT("Secret may not be longer than %u\n", MAX_LENGTH) - fclose(secret_file); - printf("Using secret of length %lu\n", secret_length); - - uint8_t a[shares_required], D[total_shares][secret_length]; - - for (uint32_t i = 0; i < secret_length; i++) { - a[0] = secret[i]; - - for (uint8_t j = 1; j < shares_required; j++) - assert(fread(&a[j], sizeof(uint8_t), 1, random) == 1); - for (uint8_t j = 0; j < total_shares; j++) - D[j][i] = calculateQ(a, shares_required, j+1); - - if (i % 32 == 0 && i != 0) - printf("Finished processing %u bytes.\n", i); - } - - char out_file_name_buf[strlen(out_file_param) + 4]; - strcpy(out_file_name_buf, out_file_param); - for (uint8_t i = 0; i < total_shares; i++) { - /*printf("%u-", i); - for (uint8_t j = 0; j < secret_length; j++) - printf("%02x", D[i][j]); - printf("\n");*/ - - sprintf(((char*)out_file_name_buf) + strlen(out_file_param), "%u", i); - FILE* out_file = fopen(out_file_name_buf, "w+"); - if (!out_file) - ERROREXIT("Could not open output file %s\n", out_file_name_buf) - - uint8_t x = i+1; - if (fwrite(&x, sizeof(uint8_t), 1, out_file) != 1) - ERROREXIT("Could not write 1 byte to %s\n", out_file_name_buf) - - if (fwrite(D[i], 1, secret_length, out_file) != secret_length) - ERROREXIT("Could not write %lu bytes to %s\n", secret_length, out_file_name_buf) - - fclose(out_file); - } - /*printf("secret = "); - for (uint8_t i = 0; i < secret_length; i++) - printf("%02x", secret[i]); - printf("\n");*/ - - // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out) - memset(secret, 0, sizeof(uint8_t)*secret_length); - memset(a, 0, sizeof(uint8_t)*shares_required); - memset(in_file, 0, strlen(in_file)); - - fclose(random); - } else { - if (!shares_required) - ERROREXIT("k must be set.\n") - - if (files_count != shares_required || in_file || !out_file_param) - ERROREXIT("Must not specify -i and must specify -o and exactly k -f s in combine mode.\n") - - uint8_t x[shares_required], q[shares_required]; - FILE* files_fps[shares_required]; - - for (uint8_t i = 0; i < shares_required; i++) { - files_fps[i] = fopen(files[i], "r"); - if (!files_fps[i]) - ERROREXIT("Couldn't open file %s for reading.\n", files[i]) - if (fread(&x[i], sizeof(uint8_t), 1, files_fps[i]) != 1) - ERROREXIT("Couldn't read the x byte of %s\n", files[i]) - } - - uint8_t secret[MAX_LENGTH]; - - uint32_t i = 0; - while (fread(&q[0], sizeof(uint8_t), 1, files_fps[0]) == 1) { - for (uint8_t j = 1; j < shares_required; j++) { - if (fread(&q[j], sizeof(uint8_t), 1, files_fps[j]) != 1) - ERROREXIT("Couldn't read next byte from %s\n", files[j]) - } - secret[i++] = calculateSecret(x, q, shares_required); - } - printf("Got secret of length %u\n", i); - - FILE* out_file = fopen(out_file_param, "w+"); - fwrite(secret, sizeof(uint8_t), i, out_file); - fclose(out_file); - - for (uint8_t i = 0; i < shares_required; i++) - fclose(files_fps[i]); - - // Clear sensitive data (No, GCC 4.7.2 is currently not optimizing this out) - memset(secret, 0, sizeof(uint8_t)*i); - memset(q, 0, sizeof(uint8_t)*shares_required); - memset(out_file_param, 0, strlen(out_file_param)); - for (uint8_t i = 0; i < shares_required; i++) - memset(files[i], 0, strlen(files[i])); - memset(x, 0, sizeof(uint8_t)*shares_required); - } - - return 0; -} #endif // !defined(TEST)