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Use constant-time comparison when checking signature validity.

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This commit is contained in:
Ken MacKay
2015-02-15 11:26:20 -08:00
parent 50621417ba
commit 98e1f208cf
1 changed files with 15 additions and 1 deletions
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uECC.c
+15 -1
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@@ -308,6 +308,7 @@ static uECC_word_t vli_testBit(const uECC_word_t *p_vli, bitcount_t p_bit);
static bitcount_t vli_numBits(const uECC_word_t *p_vli, wordcount_t p_maxWords); static bitcount_t vli_numBits(const uECC_word_t *p_vli, wordcount_t p_maxWords);
static void vli_set(uECC_word_t *p_dest, const uECC_word_t *p_src); static void vli_set(uECC_word_t *p_dest, const uECC_word_t *p_src);
static cmpresult_t vli_cmp(uECC_word_t *p_left, uECC_word_t *p_right); static cmpresult_t vli_cmp(uECC_word_t *p_left, uECC_word_t *p_right);
static cmpresult_t vli_equal(uECC_word_t *p_left, uECC_word_t *p_right);
static void vli_rshift1(uECC_word_t *p_vli); static void vli_rshift1(uECC_word_t *p_vli);
static uECC_word_t vli_add(uECC_word_t *p_result, uECC_word_t *p_left, uECC_word_t *p_right); static uECC_word_t vli_add(uECC_word_t *p_result, uECC_word_t *p_left, uECC_word_t *p_right);
static uECC_word_t vli_sub(uECC_word_t *p_result, uECC_word_t *p_left, uECC_word_t *p_right); static uECC_word_t vli_sub(uECC_word_t *p_result, uECC_word_t *p_left, uECC_word_t *p_right);
@@ -514,6 +515,19 @@ static cmpresult_t vli_cmp(uECC_word_t *p_left, uECC_word_t *p_right)
} }
#endif #endif
static cmpresult_t vli_equal(uECC_word_t *p_left, uECC_word_t *p_right)
{
uECC_word_t l_result = 0;
swordcount_t i;
for(i = uECC_WORDS-1; i >= 0; --i)
{
l_result |= (p_left[i] ^ p_right[i]);
}
return (l_result == 0);
}
/* Computes p_vli = p_vli >> 1. */ /* Computes p_vli = p_vli >> 1. */
#if !asm_rshift1 #if !asm_rshift1
static void vli_rshift1(uECC_word_t *p_vli) static void vli_rshift1(uECC_word_t *p_vli)
@@ -2331,7 +2345,7 @@ int uECC_verify(const uint8_t p_publicKey[uECC_BYTES*2], const uint8_t p_hash[uE
#endif #endif
/* Accept only if v == r. */ /* Accept only if v == r. */
return (vli_cmp(rx, r) == 0); return vli_equal(rx, r);
} }
int uECC_bytes() int uECC_bytes()