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Add invariant checking to group elements
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@sipa @gmaxwell
sipa authored and gmaxwell committed Sep 2, 2020
1 parent 5d0d350 commit 95d8d92
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6 changes: 6 additions & 0 deletions src/group.h
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Original file line number Diff line number Diff line change
Expand Up @@ -138,4 +138,10 @@ static void secp256k1_ge_storage_cmov(secp256k1_ge_storage *r, const secp256k1_g
/** 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);

/** Check invariants on an affine group element (no-op unless VERIFY is enabled). */
static void secp256k1_ge_verify(const secp256k1_ge *a);

/** Check invariants on a Jacobian group element (no-op unless VERIFY is enabled). */
static void secp256k1_gej_verify(const secp256k1_gej *a);

#endif /* SECP256K1_GROUP_H */
82 changes: 81 additions & 1 deletion src/group_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -71,34 +71,63 @@ static const secp256k1_ge secp256k1_ge_const_g = SECP256K1_GE_CONST(
static const int CURVE_B = 7;
#endif

static void secp256k1_ge_verify(const secp256k1_ge *a) {
#ifdef VERIFY
secp256k1_fe_verify(&a->x);
secp256k1_fe_verify(&a->y);
VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
#endif
(void)a;
}

static void secp256k1_gej_verify(const secp256k1_gej *a) {
#ifdef VERIFY
secp256k1_fe_verify(&a->x);
secp256k1_fe_verify(&a->y);
secp256k1_fe_verify(&a->z);
VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
#endif
(void)a;
}

static void secp256k1_ge_set_gej_zinv(secp256k1_ge *r, const secp256k1_gej *a, const secp256k1_fe *zi) {
secp256k1_fe zi2;
secp256k1_fe zi3;
secp256k1_gej_verify(a);
secp256k1_fe_verify(zi);
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;
secp256k1_ge_verify(r);
}

static void secp256k1_ge_set_xy(secp256k1_ge *r, const secp256k1_fe *x, const secp256k1_fe *y) {
secp256k1_fe_verify(x);
secp256k1_fe_verify(y);
r->infinity = 0;
r->x = *x;
r->y = *y;
secp256k1_ge_verify(r);
}

static int secp256k1_ge_is_infinity(const secp256k1_ge *a) {
secp256k1_ge_verify(a);
return a->infinity;
}

static void secp256k1_ge_neg(secp256k1_ge *r, const secp256k1_ge *a) {
secp256k1_ge_verify(a);
*r = *a;
secp256k1_fe_normalize_weak(&r->y);
secp256k1_fe_negate(&r->y, &r->y, 1);
secp256k1_ge_verify(r);
}

static void secp256k1_ge_set_gej(secp256k1_ge *r, secp256k1_gej *a) {
secp256k1_fe z2, z3;
secp256k1_gej_verify(a);
r->infinity = a->infinity;
secp256k1_fe_inv(&a->z, &a->z);
secp256k1_fe_sqr(&z2, &a->z);
Expand All @@ -108,10 +137,12 @@ 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;
secp256k1_ge_verify(r);
}

static void secp256k1_ge_set_gej_var(secp256k1_ge *r, secp256k1_gej *a) {
secp256k1_fe z2, z3;
secp256k1_gej_verify(a);
if (secp256k1_gej_is_infinity(a)) {
secp256k1_ge_set_infinity(r);
return;
Expand All @@ -125,6 +156,7 @@ static void secp256k1_ge_set_gej_var(secp256k1_ge *r, secp256k1_gej *a) {
secp256k1_fe_set_int(&a->z, 1);
r->x = a->x;
r->y = a->y;
secp256k1_ge_verify(r);
}

static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a, size_t len) {
Expand All @@ -133,6 +165,7 @@ 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++) {
secp256k1_gej_verify(&a[i]);
if (!a[i].infinity) {
/* Use destination's x coordinates as scratch space */
if (last_i == SIZE_MAX) {
Expand Down Expand Up @@ -166,6 +199,7 @@ static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a
} else {
secp256k1_ge_set_infinity(&r[i]);
}
secp256k1_ge_verify(&r[i]);
}
}

Expand All @@ -174,13 +208,16 @@ static void secp256k1_ge_globalz_set_table_gej(size_t len, secp256k1_ge *r, secp
secp256k1_fe zs;

if (len > 0) {
secp256k1_gej_verify(&a[i]);
secp256k1_fe_verify(&zr[i]);
/* The z of the final point gives us the "global Z" for the table. */
r[i].x = a[i].x;
r[i].y = a[i].y;
/* Ensure all y values are in weak normal form for fast negation of points */
secp256k1_fe_normalize_weak(&r[i].y);
*globalz = a[i].z;
r[i].infinity = 0;
secp256k1_ge_verify(&r[i]);
zs = zr[i];

/* Work our way backwards, using the z-ratios to scale the x/y values. */
Expand All @@ -199,80 +236,98 @@ static void secp256k1_gej_set_infinity(secp256k1_gej *r) {
secp256k1_fe_clear(&r->x);
secp256k1_fe_clear(&r->y);
secp256k1_fe_clear(&r->z);
secp256k1_gej_verify(r);
}

static void secp256k1_ge_set_infinity(secp256k1_ge *r) {
r->infinity = 1;
secp256k1_fe_clear(&r->x);
secp256k1_fe_clear(&r->y);
secp256k1_ge_verify(r);
}

static void secp256k1_gej_clear(secp256k1_gej *r) {
r->infinity = 0;
secp256k1_fe_clear(&r->x);
secp256k1_fe_clear(&r->y);
secp256k1_fe_clear(&r->z);
secp256k1_gej_verify(r);
}

static void secp256k1_ge_clear(secp256k1_ge *r) {
r->infinity = 0;
secp256k1_fe_clear(&r->x);
secp256k1_fe_clear(&r->y);
secp256k1_ge_verify(r);
}

static int secp256k1_ge_set_xquad(secp256k1_ge *r, const secp256k1_fe *x) {
secp256k1_fe x2, x3, c;
int ret;
secp256k1_fe_verify(x);
r->x = *x;
secp256k1_fe_sqr(&x2, x);
secp256k1_fe_mul(&x3, x, &x2);
r->infinity = 0;
secp256k1_fe_set_int(&c, CURVE_B);
secp256k1_fe_add(&c, &x3);
return secp256k1_fe_sqrt(&r->y, &c);
ret = secp256k1_fe_sqrt(&r->y, &c);
secp256k1_ge_verify(r);
return ret;
}

static int secp256k1_ge_set_xo_var(secp256k1_ge *r, const secp256k1_fe *x, int odd) {
secp256k1_fe_verify(x);
if (!secp256k1_ge_set_xquad(r, x)) {
return 0;
}
secp256k1_fe_normalize_var(&r->y);
if (secp256k1_fe_is_odd(&r->y) != odd) {
secp256k1_fe_negate(&r->y, &r->y, 1);
}
secp256k1_ge_verify(r);
return 1;

}

static void secp256k1_gej_set_ge(secp256k1_gej *r, const secp256k1_ge *a) {
secp256k1_ge_verify(a);
r->infinity = a->infinity;
r->x = a->x;
r->y = a->y;
secp256k1_fe_set_int(&r->z, 1);
secp256k1_gej_verify(r);
}

static int secp256k1_gej_eq_x_var(const secp256k1_fe *x, const secp256k1_gej *a) {
secp256k1_fe r, r2;
secp256k1_fe_verify(x);
secp256k1_gej_verify(a);
VERIFY_CHECK(!a->infinity);
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, &r2);
}

static void secp256k1_gej_neg(secp256k1_gej *r, const secp256k1_gej *a) {
secp256k1_gej_verify(a);
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);
secp256k1_gej_verify(r);
}

static int secp256k1_gej_is_infinity(const secp256k1_gej *a) {
secp256k1_gej_verify(a);
return a->infinity;
}

static int secp256k1_gej_is_valid_var(const secp256k1_gej *a) {
secp256k1_fe y2, x3, z2, z6;
secp256k1_gej_verify(a);
if (a->infinity) {
return 0;
}
Expand All @@ -293,6 +348,7 @@ static int secp256k1_gej_is_valid_var(const secp256k1_gej *a) {

static int secp256k1_ge_is_valid_var(const secp256k1_ge *a) {
secp256k1_fe y2, x3, c;
secp256k1_ge_verify(a);
if (a->infinity) {
return 0;
}
Expand All @@ -314,6 +370,7 @@ static SECP256K1_INLINE void secp256k1_gej_double(secp256k1_gej *r, const secp25
* mainly because it requires more normalizations.
*/
secp256k1_fe t1,t2,t3,t4;
secp256k1_gej_verify(a);

r->infinity = a->infinity;

Expand All @@ -337,6 +394,7 @@ static SECP256K1_INLINE void secp256k1_gej_double(secp256k1_gej *r, const secp25
secp256k1_fe_mul(&r->y, &t1, &t3); /* Y' = 36*X^3*Y^2 - 27*X^6 (1) */
secp256k1_fe_negate(&t2, &t4, 2); /* T2 = -8*Y^4 (3) */
secp256k1_fe_add(&r->y, &t2); /* Y' = 36*X^3*Y^2 - 27*X^6 - 8*Y^4 (4) */
secp256k1_gej_verify(r);
}

static void secp256k1_gej_double_var(secp256k1_gej *r, const secp256k1_gej *a, secp256k1_fe *rzr) {
Expand All @@ -350,6 +408,7 @@ 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).
*/
secp256k1_gej_verify(a);
if (a->infinity) {
secp256k1_gej_set_infinity(r);
if (rzr != NULL) {
Expand All @@ -371,6 +430,8 @@ static void secp256k1_gej_add_var(secp256k1_gej *r, const secp256k1_gej *a, cons
/* Operations: 12 mul, 4 sqr, 2 normalize, 12 mul_int/add/negate */
secp256k1_fe z22, z12, u1, u2, s1, s2, h, i, i2, h2, h3, t;

secp256k1_gej_verify(a);
secp256k1_gej_verify(b);
if (a->infinity) {
VERIFY_CHECK(rzr == NULL);
*r = *b;
Expand Down Expand Up @@ -418,11 +479,14 @@ static void secp256k1_gej_add_var(secp256k1_gej *r, const secp256k1_gej *a, cons
secp256k1_fe_negate(&r->y, &r->x, 5); secp256k1_fe_add(&r->y, &t); secp256k1_fe_mul(&r->y, &r->y, &i);
secp256k1_fe_mul(&h3, &h3, &s1); secp256k1_fe_negate(&h3, &h3, 1);
secp256k1_fe_add(&r->y, &h3);
secp256k1_gej_verify(r);
}

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, 4 normalize, 12 mul_int/add/negate */
secp256k1_fe z12, u1, u2, s1, s2, h, i, i2, h2, h3, t;
secp256k1_gej_verify(a);
secp256k1_ge_verify(b);
if (a->infinity) {
VERIFY_CHECK(rzr == NULL);
secp256k1_gej_set_ge(r, b);
Expand Down Expand Up @@ -467,16 +531,20 @@ static void secp256k1_gej_add_ge_var(secp256k1_gej *r, const secp256k1_gej *a, c
secp256k1_fe_negate(&r->y, &r->x, 5); secp256k1_fe_add(&r->y, &t); secp256k1_fe_mul(&r->y, &r->y, &i);
secp256k1_fe_mul(&h3, &h3, &s1); secp256k1_fe_negate(&h3, &h3, 1);
secp256k1_fe_add(&r->y, &h3);
secp256k1_gej_verify(r);
}

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, 4 normalize, 12 mul_int/add/negate */
secp256k1_fe az, z12, u1, u2, s1, s2, h, i, i2, h2, h3, t;

secp256k1_gej_verify(a);
secp256k1_ge_verify(b);
if (b->infinity) {
*r = *a;
return;
}
secp256k1_fe_verify(bzinv);
if (a->infinity) {
secp256k1_fe bzinv2, bzinv3;
r->infinity = b->infinity;
Expand Down Expand Up @@ -523,6 +591,7 @@ static void secp256k1_gej_add_zinv_var(secp256k1_gej *r, const secp256k1_gej *a,
secp256k1_fe_negate(&r->y, &r->x, 5); secp256k1_fe_add(&r->y, &t); secp256k1_fe_mul(&r->y, &r->y, &i);
secp256k1_fe_mul(&h3, &h3, &s1); secp256k1_fe_negate(&h3, &h3, 1);
secp256k1_fe_add(&r->y, &h3);
secp256k1_gej_verify(r);
}


Expand All @@ -534,6 +603,8 @@ static void secp256k1_gej_add_ge(secp256k1_gej *r, const secp256k1_gej *a, const
int infinity, degenerate;
VERIFY_CHECK(!b->infinity);
VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
secp256k1_gej_verify(a);
secp256k1_ge_verify(b);

/** In:
* Eric Brier and Marc Joye, Weierstrass Elliptic Curves and Side-Channel Attacks.
Expand Down Expand Up @@ -646,21 +717,26 @@ static void secp256k1_gej_add_ge(secp256k1_gej *r, const secp256k1_gej *a, const
secp256k1_fe_cmov(&r->y, &b->y, a->infinity);
secp256k1_fe_cmov(&r->z, &fe_1, a->infinity);
r->infinity = infinity;
secp256k1_gej_verify(r);
}

static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *s) {
/* Operations: 4 mul, 1 sqr */
secp256k1_fe zz;
secp256k1_gej_verify(r);
secp256k1_fe_verify(s);
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 */
secp256k1_gej_verify(r);
}

static void secp256k1_ge_to_storage(secp256k1_ge_storage *r, const secp256k1_ge *a) {
secp256k1_fe x, y;
secp256k1_ge_verify(a);
VERIFY_CHECK(!a->infinity);
x = a->x;
secp256k1_fe_normalize(&x);
Expand All @@ -674,6 +750,7 @@ 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;
secp256k1_ge_verify(r);
}

static SECP256K1_INLINE void secp256k1_ge_storage_cmov(secp256k1_ge_storage *r, const secp256k1_ge_storage *a, int flag) {
Expand All @@ -687,14 +764,17 @@ static void secp256k1_ge_mul_lambda(secp256k1_ge *r, const secp256k1_ge *a) {
0x7ae96a2bul, 0x657c0710ul, 0x6e64479eul, 0xac3434e9ul,
0x9cf04975ul, 0x12f58995ul, 0xc1396c28ul, 0x719501eeul
);
secp256k1_ge_verify(a);
*r = *a;
secp256k1_fe_mul(&r->x, &r->x, &beta);
secp256k1_ge_verify(r);
}
#endif

static int secp256k1_gej_has_quad_y_var(const secp256k1_gej *a) {
secp256k1_fe yz;

secp256k1_gej_verify(a);
if (a->infinity) {
return 0;
}
Expand Down

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