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Make secp256k1_fe_sqrt constant time

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This commit is contained in:
Pieter Wuille
2016-07-09 14:23:44 +02:00
parent e2a8e92125
commit 926836ad36
6 changed files with 24 additions and 14 deletions
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13
src/field_impl.h
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@@ -21,6 +21,13 @@
#error "Please select field implementation"
#endif
SECP256K1_INLINE static int secp256k1_fe_equal(const secp256k1_fe *a, const secp256k1_fe *b) {
secp256k1_fe na;
secp256k1_fe_negate(&na, a, 1);
secp256k1_fe_add(&na, b);
return secp256k1_fe_normalizes_to_zero(&na);
}
SECP256K1_INLINE static int secp256k1_fe_equal_var(const secp256k1_fe *a, const secp256k1_fe *b) {
secp256k1_fe na;
secp256k1_fe_negate(&na, a, 1);
@@ -28,7 +35,7 @@ SECP256K1_INLINE static int secp256k1_fe_equal_var(const secp256k1_fe *a, const
return secp256k1_fe_normalizes_to_zero_var(&na);
}
static int secp256k1_fe_sqrt_var(secp256k1_fe *r, const secp256k1_fe *a) {
static int secp256k1_fe_sqrt(secp256k1_fe *r, const secp256k1_fe *a) {
/** Given that p is congruent to 3 mod 4, we can compute the square root of
* a mod p as the (p+1)/4'th power of a.
*
@@ -123,7 +130,7 @@ static int secp256k1_fe_sqrt_var(secp256k1_fe *r, const secp256k1_fe *a) {
/* Check that a square root was actually calculated */
secp256k1_fe_sqr(&t1, r);
return secp256k1_fe_equal_var(&t1, a);
return secp256k1_fe_equal(&t1, a);
}
static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *a) {
@@ -301,7 +308,7 @@ static int secp256k1_fe_is_quad_var(const secp256k1_fe *a) {
return secp256k1_num_jacobi(&n, &m) >= 0;
#else
secp256k1_fe r;
return secp256k1_fe_sqrt_var(&r, a) == 1;
return secp256k1_fe_sqrt(&r, a);
#endif
}