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Fix for constant time (step 5)

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NIIBE Yutaka
2014-01-21 14:40:58 +09:00
parent af66c5fa08
commit f21a89588c
2 changed files with 11 additions and 6 deletions
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15
src/ec_p256.c
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@@ -406,8 +406,8 @@ point_is_on_the_curve (const ac *P)
modp256_sqr (t, P->y);
if (bn256_cmp (s, t) == 0)
return 0;
return -1;
else
return -1;
}
/**
@@ -531,7 +531,7 @@ ecdsa (bn256 *r, bn256 *s, const bn256 *z, const bn256 *d)
bn512 tmp[1];
bn256 k_inv[1];
uint32_t carry;
#define borrow carry
#define tmp_k k_inv
do
@@ -545,10 +545,11 @@ ecdsa (bn256 *r, bn256 *s, const bn256 *z, const bn256 *d)
continue;
bn256_add_uint (k, k, 1);
compute_kG (KG, k);
if (bn256_is_ge (KG->x, N))
bn256_sub (r, KG->x, N);
else
borrow = bn256_sub (r, KG->x, N);
if (borrow)
memcpy (r, KG->x, sizeof (bn256));
else
memcpy (KG->x, r, sizeof (bn256));
}
while (bn256_is_zero (r));
@@ -558,6 +559,8 @@ ecdsa (bn256 *r, bn256 *s, const bn256 *z, const bn256 *d)
carry = bn256_add (s, s, z);
if (carry)
bn256_sub (s, s, N);
else
bn256_sub (tmp, s, N);
bn256_mul (tmp, s, k_inv);
mod_reduce (s, tmp, N, MU_lower);
}