Add invariant checking to group elements

This commit is contained in:
Pieter Wuille 2020-09-01 17:59:51 -07:00
parent a18821d5b1
commit f20266722a
2 changed files with 191 additions and 5 deletions

View File

@ -164,4 +164,12 @@ static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *b);
*/
static int secp256k1_ge_is_in_correct_subgroup(const secp256k1_ge* ge);
#ifdef VERIFY
/** Check invariants on an affine group element. */
static void secp256k1_ge_verify(const secp256k1_ge *a);
/** Check invariants on a Jacobian group element. */
static void secp256k1_gej_verify(const secp256k1_gej *a);
#endif
#endif /* SECP256K1_GROUP_H */

View File

@ -73,35 +73,78 @@ static const secp256k1_ge secp256k1_ge_const_g = SECP256K1_G;
#endif
/* End of section generated by sage/gen_exhaustive_groups.sage. */
#ifdef VERIFY
static void secp256k1_ge_verify(const secp256k1_ge *a) {
secp256k1_fe_verify(&a->x);
secp256k1_fe_verify(&a->y);
VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
}
static void secp256k1_gej_verify(const secp256k1_gej *a) {
secp256k1_fe_verify(&a->x);
secp256k1_fe_verify(&a->y);
secp256k1_fe_verify(&a->z);
VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
}
#endif
static void secp256k1_ge_set_gej_zinv(secp256k1_ge *r, const secp256k1_gej *a, const secp256k1_fe *zi) {
secp256k1_fe zi2;
secp256k1_fe zi3;
#ifdef VERIFY
/* Do not call secp256k1_ge_verify, as we do not require a->z to be initialized. */
secp256k1_fe_verify(&a->x);
secp256k1_fe_verify(&a->y);
secp256k1_fe_verify(zi);
#endif
VERIFY_CHECK(!a->infinity);
secp256k1_fe_sqr(&zi2, zi);
secp256k1_fe_mul(&zi3, &zi2, zi);
secp256k1_fe_mul(&r->x, &a->x, &zi2);
secp256k1_fe_mul(&r->y, &a->y, &zi3);
r->infinity = a->infinity;
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static void secp256k1_ge_set_xy(secp256k1_ge *r, const secp256k1_fe *x, const secp256k1_fe *y) {
#ifdef VERIFY
secp256k1_fe_verify(x);
secp256k1_fe_verify(y);
#endif
r->infinity = 0;
r->x = *x;
r->y = *y;
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static int secp256k1_ge_is_infinity(const secp256k1_ge *a) {
#ifdef VERIFY
secp256k1_ge_verify(a);
#endif
return a->infinity;
}
static void secp256k1_ge_neg(secp256k1_ge *r, const secp256k1_ge *a) {
#ifdef VERIFY
secp256k1_ge_verify(a);
#endif
*r = *a;
secp256k1_fe_normalize_weak(&r->y);
secp256k1_fe_negate(&r->y, &r->y, 1);
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static void secp256k1_ge_set_gej(secp256k1_ge *r, secp256k1_gej *a) {
secp256k1_fe z2, z3;
#ifdef VERIFY
secp256k1_gej_verify(a);
#endif
r->infinity = a->infinity;
secp256k1_fe_inv(&a->z, &a->z);
secp256k1_fe_sqr(&z2, &a->z);
@ -111,10 +154,16 @@ static void secp256k1_ge_set_gej(secp256k1_ge *r, secp256k1_gej *a) {
secp256k1_fe_set_int(&a->z, 1);
r->x = a->x;
r->y = a->y;
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static void secp256k1_ge_set_gej_var(secp256k1_ge *r, secp256k1_gej *a) {
secp256k1_fe z2, z3;
#ifdef VERIFY
secp256k1_gej_verify(a);
#endif
if (secp256k1_gej_is_infinity(a)) {
secp256k1_ge_set_infinity(r);
return;
@ -127,6 +176,9 @@ static void secp256k1_ge_set_gej_var(secp256k1_ge *r, secp256k1_gej *a) {
secp256k1_fe_mul(&a->y, &a->y, &z3);
secp256k1_fe_set_int(&a->z, 1);
secp256k1_ge_set_xy(r, &a->x, &a->y);
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a, size_t len) {
@ -135,6 +187,9 @@ static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a
size_t last_i = SIZE_MAX;
for (i = 0; i < len; i++) {
#ifdef VERIFY
secp256k1_gej_verify(&a[i]);
#endif
if (a[i].infinity) {
secp256k1_ge_set_infinity(&r[i]);
} else {
@ -168,6 +223,9 @@ static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a
if (!a[i].infinity) {
secp256k1_ge_set_gej_zinv(&r[i], &a[i], &r[i].x);
}
#ifdef VERIFY
secp256k1_ge_verify(&r[i]);
#endif
}
}
@ -176,6 +234,11 @@ static void secp256k1_ge_table_set_globalz(size_t len, secp256k1_ge *a, const se
secp256k1_fe zs;
if (len > 0) {
#ifdef VERIFY
/* Verify inputs a[len-1] and zr[len-1]. */
secp256k1_ge_verify(&a[i]);
secp256k1_fe_verify(&zr[i]);
#endif
/* Ensure all y values are in weak normal form for fast negation of points */
secp256k1_fe_normalize_weak(&a[i].y);
zs = zr[i];
@ -183,6 +246,11 @@ static void secp256k1_ge_table_set_globalz(size_t len, secp256k1_ge *a, const se
/* Work our way backwards, using the z-ratios to scale the x/y values. */
while (i > 0) {
secp256k1_gej tmpa;
#ifdef VERIFY
/* Verify all inputs a[i] and zr[i]. */
secp256k1_fe_verify(&zr[i]);
secp256k1_ge_verify(&a[i]);
#endif
if (i != len - 1) {
secp256k1_fe_mul(&zs, &zs, &zr[i]);
}
@ -191,6 +259,10 @@ static void secp256k1_ge_table_set_globalz(size_t len, secp256k1_ge *a, const se
tmpa.y = a[i].y;
tmpa.infinity = 0;
secp256k1_ge_set_gej_zinv(&a[i], &tmpa, &zs);
#ifdef VERIFY
/* Verify the output a[i]. */
secp256k1_ge_verify(&a[i]);
#endif
}
}
}
@ -200,12 +272,18 @@ static void secp256k1_gej_set_infinity(secp256k1_gej *r) {
secp256k1_fe_clear(&r->x);
secp256k1_fe_clear(&r->y);
secp256k1_fe_clear(&r->z);
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static void secp256k1_ge_set_infinity(secp256k1_ge *r) {
r->infinity = 1;
secp256k1_fe_clear(&r->x);
secp256k1_fe_clear(&r->y);
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static void secp256k1_gej_clear(secp256k1_gej *r) {
@ -223,31 +301,45 @@ static void secp256k1_ge_clear(secp256k1_ge *r) {
static int secp256k1_ge_set_xo_var(secp256k1_ge *r, const secp256k1_fe *x, int odd) {
secp256k1_fe x2, x3;
int ret;
#ifdef VERIFY
secp256k1_fe_verify(x);
#endif
r->x = *x;
secp256k1_fe_sqr(&x2, x);
secp256k1_fe_mul(&x3, x, &x2);
r->infinity = 0;
secp256k1_fe_add_int(&x3, SECP256K1_B);
if (!secp256k1_fe_sqrt(&r->y, &x3)) {
return 0;
}
ret = secp256k1_fe_sqrt(&r->y, &x3);
secp256k1_fe_normalize_var(&r->y);
if (secp256k1_fe_is_odd(&r->y) != odd) {
secp256k1_fe_negate(&r->y, &r->y, 1);
}
return 1;
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
return ret;
}
static void secp256k1_gej_set_ge(secp256k1_gej *r, const secp256k1_ge *a) {
#ifdef VERIFY
secp256k1_ge_verify(a);
#endif
r->infinity = a->infinity;
r->x = a->x;
r->y = a->y;
secp256k1_fe_set_int(&r->z, 1);
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static int secp256k1_gej_eq_var(const secp256k1_gej *a, const secp256k1_gej *b) {
secp256k1_gej tmp;
#ifdef VERIFY
secp256k1_gej_verify(b);
secp256k1_gej_verify(a);
#endif
secp256k1_gej_neg(&tmp, a);
secp256k1_gej_add_var(&tmp, &tmp, b, NULL);
return secp256k1_gej_is_infinity(&tmp);
@ -255,6 +347,10 @@ 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) {
secp256k1_fe r, r2;
#ifdef VERIFY
secp256k1_fe_verify(x);
secp256k1_gej_verify(a);
#endif
VERIFY_CHECK(!a->infinity);
secp256k1_fe_sqr(&r, &a->z); secp256k1_fe_mul(&r, &r, x);
r2 = a->x; secp256k1_fe_normalize_weak(&r2);
@ -262,20 +358,32 @@ static int secp256k1_gej_eq_x_var(const secp256k1_fe *x, const secp256k1_gej *a)
}
static void secp256k1_gej_neg(secp256k1_gej *r, const secp256k1_gej *a) {
#ifdef VERIFY
secp256k1_gej_verify(a);
#endif
r->infinity = a->infinity;
r->x = a->x;
r->y = a->y;
r->z = a->z;
secp256k1_fe_normalize_weak(&r->y);
secp256k1_fe_negate(&r->y, &r->y, 1);
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static int secp256k1_gej_is_infinity(const secp256k1_gej *a) {
#ifdef VERIFY
secp256k1_gej_verify(a);
#endif
return a->infinity;
}
static int secp256k1_ge_is_valid_var(const secp256k1_ge *a) {
secp256k1_fe y2, x3;
#ifdef VERIFY
secp256k1_ge_verify(a);
#endif
if (a->infinity) {
return 0;
}
@ -291,6 +399,9 @@ static SECP256K1_INLINE void secp256k1_gej_double(secp256k1_gej *r, const secp25
/* Operations: 3 mul, 4 sqr, 8 add/half/mul_int/negate */
secp256k1_fe l, s, t;
#ifdef VERIFY
secp256k1_gej_verify(a);
#endif
r->infinity = a->infinity;
/* Formula used:
@ -317,6 +428,9 @@ static SECP256K1_INLINE void secp256k1_gej_double(secp256k1_gej *r, const secp25
secp256k1_fe_mul(&r->y, &t, &l); /* Y3 = L*(X3 + T) (1) */
secp256k1_fe_add(&r->y, &s); /* Y3 = L*(X3 + T) + S^2 (2) */
secp256k1_fe_negate(&r->y, &r->y, 2); /* Y3 = -(L*(X3 + T) + S^2) (3) */
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static void secp256k1_gej_double_var(secp256k1_gej *r, const secp256k1_gej *a, secp256k1_fe *rzr) {
@ -330,6 +444,9 @@ static void secp256k1_gej_double_var(secp256k1_gej *r, const secp256k1_gej *a, s
* the infinity flag even though the point doubles to infinity, and the result
* point will be gibberish (z = 0 but infinity = 0).
*/
#ifdef VERIFY
secp256k1_gej_verify(a);
#endif
if (a->infinity) {
secp256k1_gej_set_infinity(r);
if (rzr != NULL) {
@ -344,12 +461,19 @@ static void secp256k1_gej_double_var(secp256k1_gej *r, const secp256k1_gej *a, s
}
secp256k1_gej_double(r, a);
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static void secp256k1_gej_add_var(secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_gej *b, secp256k1_fe *rzr) {
/* 12 mul, 4 sqr, 11 add/negate/normalizes_to_zero (ignoring special cases) */
secp256k1_fe z22, z12, u1, u2, s1, s2, h, i, h2, h3, t;
#ifdef VERIFY
secp256k1_gej_verify(a);
secp256k1_gej_verify(b);
#endif
if (a->infinity) {
VERIFY_CHECK(rzr == NULL);
*r = *b;
@ -404,11 +528,18 @@ static void secp256k1_gej_add_var(secp256k1_gej *r, const secp256k1_gej *a, cons
secp256k1_fe_mul(&r->y, &t, &i);
secp256k1_fe_mul(&h3, &h3, &s1);
secp256k1_fe_add(&r->y, &h3);
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static void secp256k1_gej_add_ge_var(secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_ge *b, secp256k1_fe *rzr) {
/* 8 mul, 3 sqr, 13 add/negate/normalize_weak/normalizes_to_zero (ignoring special cases) */
secp256k1_fe z12, u1, u2, s1, s2, h, i, h2, h3, t;
#ifdef VERIFY
secp256k1_gej_verify(a);
secp256k1_ge_verify(b);
#endif
if (a->infinity) {
VERIFY_CHECK(rzr == NULL);
secp256k1_gej_set_ge(r, b);
@ -461,12 +592,20 @@ static void secp256k1_gej_add_ge_var(secp256k1_gej *r, const secp256k1_gej *a, c
secp256k1_fe_mul(&r->y, &t, &i);
secp256k1_fe_mul(&h3, &h3, &s1);
secp256k1_fe_add(&r->y, &h3);
#ifdef VERIFY
secp256k1_gej_verify(r);
if (rzr != NULL) secp256k1_fe_verify(rzr);
#endif
}
static void secp256k1_gej_add_zinv_var(secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_ge *b, const secp256k1_fe *bzinv) {
/* 9 mul, 3 sqr, 13 add/negate/normalize_weak/normalizes_to_zero (ignoring special cases) */
secp256k1_fe az, z12, u1, u2, s1, s2, h, i, h2, h3, t;
#ifdef VERIFY
secp256k1_ge_verify(b);
secp256k1_fe_verify(bzinv);
#endif
if (a->infinity) {
secp256k1_fe bzinv2, bzinv3;
r->infinity = b->infinity;
@ -525,6 +664,9 @@ static void secp256k1_gej_add_zinv_var(secp256k1_gej *r, const secp256k1_gej *a,
secp256k1_fe_mul(&r->y, &t, &i);
secp256k1_fe_mul(&h3, &h3, &s1);
secp256k1_fe_add(&r->y, &h3);
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
@ -533,6 +675,10 @@ static void secp256k1_gej_add_ge(secp256k1_gej *r, const secp256k1_gej *a, const
secp256k1_fe zz, u1, u2, s1, s2, t, tt, m, n, q, rr;
secp256k1_fe m_alt, rr_alt;
int degenerate;
#ifdef VERIFY
secp256k1_gej_verify(a);
secp256k1_ge_verify(b);
#endif
VERIFY_CHECK(!b->infinity);
VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
@ -658,21 +804,34 @@ static void secp256k1_gej_add_ge(secp256k1_gej *r, const secp256k1_gej *a, const
* We have degenerate = false, r->z = (y1 + y2) * Z.
* Then r->infinity = ((y1 + y2)Z == 0) = (y1 == -y2) = false. */
r->infinity = secp256k1_fe_normalizes_to_zero(&r->z);
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *s) {
/* Operations: 4 mul, 1 sqr */
secp256k1_fe zz;
#ifdef VERIFY
secp256k1_gej_verify(r);
secp256k1_fe_verify(s);
#endif
VERIFY_CHECK(!secp256k1_fe_is_zero(s));
secp256k1_fe_sqr(&zz, s);
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 */
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static void secp256k1_ge_to_storage(secp256k1_ge_storage *r, const secp256k1_ge *a) {
secp256k1_fe x, y;
#ifdef VERIFY
secp256k1_ge_verify(a);
#endif
VERIFY_CHECK(!a->infinity);
x = a->x;
secp256k1_fe_normalize(&x);
@ -686,14 +845,24 @@ static void secp256k1_ge_from_storage(secp256k1_ge *r, const secp256k1_ge_storag
secp256k1_fe_from_storage(&r->x, &a->x);
secp256k1_fe_from_storage(&r->y, &a->y);
r->infinity = 0;
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static SECP256K1_INLINE void secp256k1_gej_cmov(secp256k1_gej *r, const secp256k1_gej *a, int flag) {
#ifdef VERIFY
secp256k1_gej_verify(r);
secp256k1_gej_verify(a);
#endif
secp256k1_fe_cmov(&r->x, &a->x, flag);
secp256k1_fe_cmov(&r->y, &a->y, flag);
secp256k1_fe_cmov(&r->z, &a->z, flag);
r->infinity ^= (r->infinity ^ a->infinity) & flag;
#ifdef VERIFY
secp256k1_gej_verify(r);
#endif
}
static SECP256K1_INLINE void secp256k1_ge_storage_cmov(secp256k1_ge_storage *r, const secp256k1_ge_storage *a, int flag) {
@ -703,7 +872,13 @@ static SECP256K1_INLINE void secp256k1_ge_storage_cmov(secp256k1_ge_storage *r,
static void secp256k1_ge_mul_lambda(secp256k1_ge *r, const secp256k1_ge *a) {
*r = *a;
#ifdef VERIFY
secp256k1_ge_verify(a);
#endif
secp256k1_fe_mul(&r->x, &r->x, &secp256k1_const_beta);
#ifdef VERIFY
secp256k1_ge_verify(r);
#endif
}
static int secp256k1_ge_is_in_correct_subgroup(const secp256k1_ge* ge) {
@ -711,6 +886,9 @@ static int secp256k1_ge_is_in_correct_subgroup(const secp256k1_ge* ge) {
secp256k1_gej out;
int i;
#ifdef VERIFY
secp256k1_ge_verify(ge);
#endif
/* A very simple EC multiplication ladder that avoids a dependency on ecmult. */
secp256k1_gej_set_infinity(&out);
for (i = 0; i < 32; ++i) {