Fix share id == 0 check for share at index 0

[shamirs] / shamirssecret.c

diff --git a/shamirssecret.c b/shamirssecret.c
index 2d6e7aac0c9a77bc41d9fc12465fd400bf82a2e6..f5ca5c5f135f6bd7eaad98d95e7c8905f0e2ea3f 100644 (file)
--- a/shamirssecret.c
+++ b/shamirssecret.c
@@ -1,34 +1,39 @@
 /*
- * Shamir's secret sharing sharing implementation
+ * Shamir's secret sharing implementation
  *
  * Copyright (C) 2013 Matt Corallo <git@bluematt.me>
  *
- * 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 file is part of ASSS (Audit-friendly Shamir's Secret Sharing)
  *
- * 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.
+ * 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.
  *
- * 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.
+ * 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/>.
  */
 
-#include <stdint.h>
-
 #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)
  */
@@ -87,7 +92,7 @@ static const uint8_t log[P] = {
        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)
@@ -110,7 +115,7 @@ static uint8_t field_invert(uint8_t a) {
 }
 
 // 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)
@@ -185,9 +190,9 @@ int main() {
  * 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;
@@ -199,10 +204,10 @@ uint8_t calculateQ(uint8_t coefficients[], uint8_t shares_required, uint8_t x) {
 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]));