-#include <stdint.h>
+/*
+ * Shamir's secret sharing implementation
+ *
+ * Copyright (C) 2013 Matt Corallo <git@bluematt.me>
+ *
+ * This file is part of ASSS (Audit-friendly Shamir's Secret Sharing)
+ *
+ * ASSS is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version.
+ *
+ * ASSS is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with ASSS. If not, see
+ * <http://www.gnu.org/licenses/>.
+ */
#ifndef IN_KERNEL
#include <assert.h>
#define CHECKSTATE(x) assert(x)
#else
#include <linux/bug.h>
-#define CHECKSTATE(x) BUG_ON(x)
+#define CHECKSTATE(x) BUG_ON(!(x))
#endif
#include "shamirssecret.h"
+#ifndef noinline
+#define noinline __attribute__((noinline))
+#endif
+
/*
* Calculations across the finite field GF(2^8)
*/
0x4a, 0xed, 0xde, 0xc5, 0x31, 0xfe, 0x18, 0x0d, 0x63, 0x8c, 0x80, 0xc0, 0xf7, 0x70, 0x07};
// We disable lots of optimizations that result in non-constant runtime (+/- branch delays)
-static uint8_t field_mul_ret(uint8_t calc, uint8_t a, uint8_t b) __attribute__((optimize("-O0"))) __attribute__((noinline));
+static uint8_t field_mul_ret(uint8_t calc, uint8_t a, uint8_t b) __attribute__((optimize("-O0"))) noinline;
static uint8_t field_mul_ret(uint8_t calc, uint8_t a, uint8_t b) {
uint8_t ret, ret2;
if (a == 0)
}
// We disable lots of optimizations that result in non-constant runtime (+/- branch delays)
-static uint8_t field_pow_ret(uint8_t calc, uint8_t a, uint8_t e) __attribute__((optimize("-O0"))) __attribute__((noinline));
+static uint8_t field_pow_ret(uint8_t calc, uint8_t a, uint8_t e) __attribute__((optimize("-O0"))) noinline;
static uint8_t field_pow_ret(uint8_t calc, uint8_t a, uint8_t e) {
uint8_t ret, ret2;
if (a == 0)
* coefficients[0] == secret, the rest are random values
*/
uint8_t calculateQ(uint8_t coefficients[], uint8_t shares_required, uint8_t x) {
+ uint8_t ret = coefficients[0], i;
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++) {
+ for (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 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 < shares_required; i++) {
+ uint8_t ret = 0, i, j;
+ for (i = 0; i < shares_required; i++) {
uint8_t temp = q[i];
- for (uint8_t j = 0; j < shares_required; j++) {
+ for (j = 0; j < shares_required; j++) {
if (i == j)
continue;
temp = field_mul(temp, field_neg(x[j]));