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Random initial Z when calculating the public key

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This commit is contained in:
Ken MacKay
2020-10-12 16:49:35 -07:00
parent 1e6e86fa43
commit d1ab664e02
1 changed files with 36 additions and 27 deletions
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uECC.c
+36 -27
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@@ -917,19 +917,54 @@ static uECC_word_t regularize_k(const uECC_word_t * const k,
return carry;
}
/* Generates a random integer in the range 0 < random < top.
Both random and top have num_words words. */
uECC_VLI_API int uECC_generate_random_int(uECC_word_t *random,
const uECC_word_t *top,
wordcount_t num_words) {
uECC_word_t mask = (uECC_word_t)-1;
uECC_word_t tries;
bitcount_t num_bits = uECC_vli_numBits(top, num_words);
if (!g_rng_function) {
return 0;
}
for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) {
if (!g_rng_function((uint8_t *)random, num_words * uECC_WORD_SIZE)) {
return 0;
}
random[num_words - 1] &= mask >> ((bitcount_t)(num_words * uECC_WORD_SIZE * 8 - num_bits));
if (!uECC_vli_isZero(random, num_words) &&
uECC_vli_cmp(top, random, num_words) == 1) {
return 1;
}
}
return 0;
}
static uECC_word_t EccPoint_compute_public_key(uECC_word_t *result,
uECC_word_t *private_key,
uECC_Curve curve) {
uECC_word_t tmp1[uECC_MAX_WORDS];
uECC_word_t tmp2[uECC_MAX_WORDS];
uECC_word_t *p2[2] = {tmp1, tmp2};
uECC_word_t *initial_Z = 0;
uECC_word_t carry;
/* Regularize the bitcount for the private key so that attackers cannot use a side channel
attack to learn the number of leading zeros. */
carry = regularize_k(private_key, tmp1, tmp2, curve);
EccPoint_mult(result, curve->G, p2[!carry], 0, curve->num_n_bits + 1, curve);
/* If an RNG function was specified, try to get a random initial Z value to improve
protection against side-channel attacks. */
if (g_rng_function) {
if (!uECC_generate_random_int(p2[carry], curve->p, curve->num_words)) {
return 0;
}
initial_Z = p2[carry];
}
EccPoint_mult(result, curve->G, p2[!carry], initial_Z, curve->num_n_bits + 1, curve);
if (EccPoint_isZero(result, curve)) {
return 0;
@@ -980,32 +1015,6 @@ uECC_VLI_API void uECC_vli_bytesToNative(uECC_word_t *native,
#endif /* uECC_WORD_SIZE */
/* Generates a random integer in the range 0 < random < top.
Both random and top have num_words words. */
uECC_VLI_API int uECC_generate_random_int(uECC_word_t *random,
const uECC_word_t *top,
wordcount_t num_words) {
uECC_word_t mask = (uECC_word_t)-1;
uECC_word_t tries;
bitcount_t num_bits = uECC_vli_numBits(top, num_words);
if (!g_rng_function) {
return 0;
}
for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) {
if (!g_rng_function((uint8_t *)random, num_words * uECC_WORD_SIZE)) {
return 0;
}
random[num_words - 1] &= mask >> ((bitcount_t)(num_words * uECC_WORD_SIZE * 8 - num_bits));
if (!uECC_vli_isZero(random, num_words) &&
uECC_vli_cmp(top, random, num_words) == 1) {
return 1;
}
}
return 0;
}
int uECC_make_key(uint8_t *public_key,
uint8_t *private_key,
uECC_Curve curve) {