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Use constant-time vli_isZero() and vli_equal() functions.

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This commit is contained in:
Ken MacKay
2015-08-23 13:00:15 -07:00
parent a6a4bdd5e0
commit c250083ccd
1 changed files with 23 additions and 8 deletions
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uECC.c
+23 -8
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@@ -83,13 +83,12 @@ static void vli_clear(uECC_word_t *vli, wordcount_t num_words) {
/* Returns 1 if vli == 0, 0 otherwise. */
static uECC_word_t vli_isZero(const uECC_word_t *vli, wordcount_t num_words) {
uECC_word_t bits = 0;
wordcount_t i;
for (i = 0; i < num_words; ++i) {
if (vli[i]) {
return 0;
}
bits |= vli[i];
}
return 1;
return (bits == 0);
}
/* Returns nonzero if bit 'bit' of vli is set. */
@@ -149,6 +148,17 @@ static cmpresult_t vli_cmp(const uECC_word_t *left,
return 0;
}
static uECC_word_t vli_equal(const uECC_word_t *left,
const uECC_word_t *right,
wordcount_t num_words) {
uECC_word_t diff = 0;
swordcount_t i;
for (i = num_words - 1; i >= 0; --i) {
diff |= (left[i] ^ right[i]);
}
return (diff == 0);
}
/* Computes vli = vli >> 1. */
static void vli_rshift1(uECC_word_t *vli, wordcount_t num_words) {
uECC_word_t *end = vli;
@@ -570,8 +580,7 @@ static void vli_modInv(uECC_word_t *result,
/* Returns 1 if 'point' is the point at infinity, 0 otherwise. */
static cmpresult_t EccPoint_isZero(const uECC_word_t *point, uECC_Curve curve) {
return vli_isZero(point, curve->num_words) &&
vli_isZero(point + curve->num_words, curve->num_words);
return vli_isZero(point, curve->num_words * 2);
}
/* Point multiplication algorithm using Montgomery's ladder with co-Z coordinates.
@@ -958,7 +967,7 @@ int uECC_valid_public_key(const uint8_t *public_key, uECC_Curve curve) {
curve->x_side(tmp2, public, curve); /* tmp2 = x^3 + ax + b */
/* Make sure that y^2 == x^3 + ax + b */
return (vli_cmp(tmp1, tmp2, curve->num_words) == 0);
return (vli_equal(tmp1, tmp2, curve->num_words));
}
int uECC_compute_public_key(const uint8_t *private_key, uint8_t *public_key, uECC_Curve curve) {
@@ -1283,7 +1292,7 @@ int uECC_verify(const uint8_t *public_key,
}
/* Accept only if v == r. */
return (vli_cmp(rx, r, curve->num_words) == 0);
return (vli_equal(rx, r, curve->num_words));
}
@@ -1357,6 +1366,12 @@ int uECC_vli_cmp(const uECC_word_t *left,
return vli_cmp(left, right, num_words);
}
int uECC_vli_equal(const uECC_word_t *left,
const uECC_word_t *right,
unsigned num_words) {
return vli_equal(left, right, num_words);
}
void uECC_vli_rshift1(uECC_word_t *vli, unsigned num_words) {
vli_rshift1(vli, num_words);
}