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Addressed review comments to PR #58. Main change:

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Removed clamping via subtraction update in the uECC_generate_random_int function.
This commit is contained in:
Evgeni Margolis
2015-10-12 21:29:57 -07:00
committed by Ken MacKay
parent 7b115fdf93
commit 12651728ea
2 changed files with 12 additions and 18 deletions
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uECC.c
+11 -17
View File
@@ -4,7 +4,7 @@
#include "uECC_vli.h" #include "uECC_vli.h"
#ifndef uECC_RNG_MAX_TRIES #ifndef uECC_RNG_MAX_TRIES
#define uECC_RNG_MAX_TRIES 4 #define uECC_RNG_MAX_TRIES 64
#endif #endif
#if uECC_SUPPORTS_secp160r1 #if uECC_SUPPORTS_secp160r1
@@ -845,14 +845,10 @@ uECC_VLI_API void uECC_vli_bytesToNative(uECC_word_t *native,
#endif /* uECC_WORD_SIZE */ #endif /* uECC_WORD_SIZE */
/* Generates a random integer in the range 0 < random < top. /* Generates a random integer in the range 0 < random < top.
Both, random and top, have num_words words. */ Both random and top have num_words words. */
uECC_VLI_API int uECC_generate_random_int(uECC_word_t *random, uECC_VLI_API int uECC_generate_random_int(uECC_word_t *random,
const uECC_word_t *top, const uECC_word_t *top,
wordcount_t num_words) { wordcount_t num_words) {
uECC_word_t random1[uECC_MAX_WORDS];
uECC_word_t random2[uECC_MAX_WORDS];
uECC_word_t *p2[2] = {random1, random2};
uECC_word_t borrow;
uECC_word_t mask = (uECC_word_t)-1; uECC_word_t mask = (uECC_word_t)-1;
uECC_word_t tries; uECC_word_t tries;
bitcount_t num_bits = uECC_vli_numBits(top, num_words); bitcount_t num_bits = uECC_vli_numBits(top, num_words);
@@ -862,14 +858,14 @@ uECC_VLI_API int uECC_generate_random_int(uECC_word_t *random,
} }
for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) { for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) {
if (g_rng_function((uint8_t *)random1, num_words * uECC_WORD_SIZE)) { if (!g_rng_function((uint8_t *)random, num_words * uECC_WORD_SIZE)) {
return 0;
}
else {
random[num_words - 1] &= mask >> ((bitcount_t)(num_words * uECC_WORD_SIZE * 8 - num_bits));
random1[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) {
borrow = uECC_vli_sub(random2, random1, top, num_words);
if (!uECC_vli_isZero(p2[!borrow], num_words)) {
uECC_vli_set(random, p2[!borrow], num_words);
return 1; return 1;
} }
} }
@@ -1081,10 +1077,8 @@ static int uECC_sign_with_k(const uint8_t *private_key,
if (!g_rng_function) { if (!g_rng_function) {
uECC_vli_clear(tmp, num_n_words); uECC_vli_clear(tmp, num_n_words);
tmp[0] = 1; tmp[0] = 1;
} else { } else if (!uECC_generate_random_int(tmp, curve->n, num_n_words)) {
if (!uECC_generate_random_int(tmp, curve->n, num_n_words)) { return 0;
return 0;
}
} }
/* Prevent side channel analysis of uECC_vli_modInv() to determine /* Prevent side channel analysis of uECC_vli_modInv() to determine
uECC_vli.h
+1 -1
View File
@@ -156,7 +156,7 @@ void uECC_point_mult(uECC_word_t *result,
uECC_Curve curve); uECC_Curve curve);
/* Generates a random integer in the range 0 < random < top. /* Generates a random integer in the range 0 < random < top.
Both, random and top, have num_words words. */ Both random and top have num_words words. */
int uECC_generate_random_int(uECC_word_t *random, int uECC_generate_random_int(uECC_word_t *random,
const uECC_word_t *top, const uECC_word_t *top,
wordcount_t num_words); wordcount_t num_words);