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Copy the 's' parameter of _gej_rescale to avoid aliasing issues #1785

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Copy the 's' parameter of _gej_rescale to avoid aliasing issues #1785

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4 changes: 2 additions & 2 deletions src/group.h
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Original file line number Diff line number Diff line change
Expand Up @@ -175,8 +175,8 @@ static void secp256k1_gej_cmov(secp256k1_gej *r, const secp256k1_gej *a, int fla
/** If flag is true, set *r equal to *a; otherwise leave it. Constant-time. Both *r and *a must be initialized.*/
static void secp256k1_ge_storage_cmov(secp256k1_ge_storage *r, const secp256k1_ge_storage *a, int flag);

/** Rescale a jacobian point by b which must be non-zero. Constant-time. */
static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *b);
/** Rescale a jacobian point by s which must be non-zero. Constant-time. */
static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *s);

/** Convert a group element that is not infinity to a 64-byte array. The output
* array is platform-dependent. */
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9 changes: 5 additions & 4 deletions src/group_impl.h
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Expand Up @@ -860,16 +860,17 @@ static void secp256k1_gej_add_ge(secp256k1_gej *r, const secp256k1_gej *a, const

static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *s) {
/* Operations: 4 mul, 1 sqr */
secp256k1_fe zz;
secp256k1_fe z, zz;
SECP256K1_GEJ_VERIFY(r);
SECP256K1_FE_VERIFY(s);
VERIFY_CHECK(!secp256k1_fe_normalizes_to_zero_var(s));

secp256k1_fe_sqr(&zz, s);
z = *s;
secp256k1_fe_sqr(&zz, &z);
secp256k1_fe_mul(&r->x, &r->x, &zz); /* r->x *= s^2 */
secp256k1_fe_mul(&r->y, &r->y, &zz);
secp256k1_fe_mul(&r->y, &r->y, s); /* r->y *= s^3 */
secp256k1_fe_mul(&r->z, &r->z, s); /* r->z *= s */
secp256k1_fe_mul(&r->y, &r->y, &z); /* r->y *= s^3 */
secp256k1_fe_mul(&r->z, &r->z, &z); /* r->z *= s */

SECP256K1_GEJ_VERIFY(r);
}
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