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group: remove unneeded normalize_weak in secp256k1_gej_eq_x_var

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By requiring that the input group element's X coordinate (`a->x`) has a
magnitude of <= 31, the normalize_weak call and also the field element
variable `r2` are not needed anymore and hence can be dropped.
This commit is contained in:
Sebastian Falbesoner 2023-06-14 17:15:46 +02:00
parent efa76c4bf7
commit 07c0e8b82e
2 changed files with 9 additions and 4 deletions
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3
src/group.h
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@ -100,7 +100,8 @@ static void secp256k1_gej_set_ge(secp256k1_gej *r, const secp256k1_ge *a);
/** Check two group elements (jacobian) for equality in variable time. */ /** Check two group elements (jacobian) for equality in variable time. */
static int secp256k1_gej_eq_var(const secp256k1_gej *a, const secp256k1_gej *b); static int secp256k1_gej_eq_var(const secp256k1_gej *a, const secp256k1_gej *b);
/** Compare the X coordinate of a group element (jacobian). */ /** Compare the X coordinate of a group element (jacobian).
* The magnitude of the group element's X coordinate must not exceed 31. */
static int secp256k1_gej_eq_x_var(const secp256k1_fe *x, const secp256k1_gej *a); static int secp256k1_gej_eq_x_var(const secp256k1_fe *x, const secp256k1_gej *a);
/** Set r equal to the inverse of a (i.e., mirrored around the X axis) */ /** Set r equal to the inverse of a (i.e., mirrored around the X axis) */

10
src/group_impl.h
View File

@ -314,13 +314,17 @@ static int secp256k1_gej_eq_var(const secp256k1_gej *a, const secp256k1_gej *b)
} }
static int secp256k1_gej_eq_x_var(const secp256k1_fe *x, const secp256k1_gej *a) { static int secp256k1_gej_eq_x_var(const secp256k1_fe *x, const secp256k1_gej *a) {
secp256k1_fe r, r2; secp256k1_fe r;
#ifdef VERIFY
secp256k1_fe_verify(x); secp256k1_fe_verify(x);
VERIFY_CHECK(a->x.magnitude <= 31);
secp256k1_gej_verify(a); secp256k1_gej_verify(a);
VERIFY_CHECK(!a->infinity); VERIFY_CHECK(!a->infinity);
#endif
secp256k1_fe_sqr(&r, &a->z); secp256k1_fe_mul(&r, &r, x); secp256k1_fe_sqr(&r, &a->z); secp256k1_fe_mul(&r, &r, x);
r2 = a->x; secp256k1_fe_normalize_weak(&r2); return secp256k1_fe_equal_var(&r, &a->x);
return secp256k1_fe_equal_var(&r, &r2);
} }
static void secp256k1_gej_neg(secp256k1_gej *r, const secp256k1_gej *a) { static void secp256k1_gej_neg(secp256k1_gej *r, const secp256k1_gej *a) {