From 7a6c59f40b44c243cecc3389db388c50e4979e07 Mon Sep 17 00:00:00 2001 From: Matt Corallo Date: Sat, 7 Sep 2013 17:44:31 -0400 Subject: [PATCH] Prepare to run in kernel mode --- shamirssecret.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/shamirssecret.c b/shamirssecret.c index 77bc0bf..9293f79 100644 --- a/shamirssecret.c +++ b/shamirssecret.c @@ -1,5 +1,12 @@ #include + +#ifndef IN_KERNEL #include +#define CHECKSTATE(x) assert(x) +#else +#include +#define CHECKSTATE(x) BUG_ON(x) +#endif #include "shamirssecret.h" @@ -21,6 +28,9 @@ static uint8_t field_neg(uint8_t 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, @@ -76,7 +86,7 @@ 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 } @@ -98,7 +108,7 @@ 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); } @@ -129,18 +139,18 @@ 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) @@ -156,7 +166,7 @@ int main() { * coefficients[0] == secret, the rest are random values */ uint8_t calculateQ(uint8_t coefficients[], uint8_t shares_required, uint8_t x) { - assert(x != 0); // q(0) == secret, though so does a[0] + 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))); -- 2.30.2