Merge bitcoin-core/secp256k1#1299: Infinity handling: ecmult_const(infinity) works, and group verification

bbc834467c5d14e3e53744211e7c4fa9d8fabe41 Avoid secp256k1_ge_set_gej_zinv with uninitialized z (Pieter Wuille)
0a2e0b2ae456c7ae60e92ddc354071f21fb6aa62 Make secp256k1_{fe,ge,gej}_verify work as no-op if non-VERIFY (Pieter Wuille)
f20266722ac93ca66d1beb0d2f2d2469b95aafea Add invariant checking to group elements (Pieter Wuille)
a18821d5b1d44db0e7c8335f338cc9876bec98cb Always initialize output coordinates in secp256k1_ge_set_gej (Pieter Wuille)
3086cb90acd9d61c5b38e862877fdeacaff74a50 Expose secp256k1_fe_verify to other modules (Pieter Wuille)
a0e696fd4da3788758bb3fdae66c7ae262dbf224 Make secp256k1_ecmult_const handle infinity (Gregory Maxwell)

Pull request description:

  Rebase of #791.

  * Clean up infinity handling, make x/y/z always initialized for infinity.
  * Make secp256k1_ecmult_const handle infinity.
    * Infinity isn't currently needed here, but correctly handling it is a little more safe against future changes.
    * Update docs for it to make it clear that it is not constant time in Q. It never was constant time in Q (and would be a little complicated to make constant time in Q: needs a constant time addition function that tracks RZR). It isn't typical for ECDH to be constant time in terms of the pubkey. If it was later made constant time in Q infinity support would be easy to preserve, e.g. by running it on a dummy value and cmoving infinity into the output.
  * Add group verification (`secp256k1_ge_verify` and `secp256k1_gej_verify`, mimicking `secp256k1_fe_verify`).
  * Make the `secp256k1_{fe,ge,gej}_verify` functions also defined (as no-ops) in non-VERIFY mode.

ACKs for top commit:
  jonasnick:
    ACK bbc834467c5d14e3e53744211e7c4fa9d8fabe41
  real-or-random:
    ACK bbc834467c5d14e3e53744211e7c4fa9d8fabe41

Tree-SHA512: 82cb51faa2c207603aa10359a311ea618fcb5a81ba175bf15515bf84043223db6428434875854cdfce9ae95f9cfd68c74e4e415f26bd574f1791b5dec1615d19

src/ecmult_const.h

@@ -11,8 +11,7 @@
 #include "group.h"
 
 /**
- * Multiply: R = q*A (in constant-time)
+ * Multiply: R = q*A (in constant-time for q)
- * A must not be infinity.
  */
 static void secp256k1_ecmult_const(secp256k1_gej *r, const secp256k1_ge *a, const secp256k1_scalar *q);
 

src/ecmult_const_impl.h

@@ -144,6 +144,11 @@ static void secp256k1_ecmult_const(secp256k1_gej *r, const secp256k1_ge *a, cons
 
     int i;
 
+    if (secp256k1_ge_is_infinity(a)) {
+        secp256k1_gej_set_infinity(r);
+        return;
+    }
+
     /* build wnaf representation for q. */
     /* split q into q_1 and q_lam (where q = q_1 + q_lam*lambda, and q_1 and q_lam are ~128 bit) */
     secp256k1_scalar_split_lambda(&q_1, &q_lam, scalar);

src/field.h

@@ -143,4 +143,7 @@ static void secp256k1_fe_get_bounds(secp256k1_fe *r, int m);
 /** Determine whether a is a square (modulo p). */
 static int secp256k1_fe_is_square_var(const secp256k1_fe *a);
 
+/** Check invariants on a field element (no-op unless VERIFY is enabled). */
+static void secp256k1_fe_verify(const secp256k1_fe *a);
+
 #endif /* SECP256K1_FIELD_H */

src/field_10x26_impl.h

@@ -21,8 +21,8 @@
  *  - 2*M*(2^26-1) is the max (inclusive) of the remaining limbs
  */
 
-#ifdef VERIFY
 static void secp256k1_fe_verify(const secp256k1_fe *a) {
+#ifdef VERIFY
     const uint32_t *d = a->n;
     int m = a->normalized ? 1 : 2 * a->magnitude, r = 1;
     r &= (d[0] <= 0x3FFFFFFUL * m);
@@ -47,8 +47,9 @@ static void secp256k1_fe_verify(const secp256k1_fe *a) {
         }
     }
     VERIFY_CHECK(r == 1);
-}
 #endif
+    (void)a;
+}
 
 static void secp256k1_fe_get_bounds(secp256k1_fe *r, int m) {
     VERIFY_CHECK(m >= 0);
@@ -458,9 +459,7 @@ SECP256K1_INLINE static void secp256k1_fe_mul_int(secp256k1_fe *r, int a) {
 }
 
 SECP256K1_INLINE static void secp256k1_fe_add(secp256k1_fe *r, const secp256k1_fe *a) {
-#ifdef VERIFY
     secp256k1_fe_verify(a);
-#endif
     r->n[0] += a->n[0];
     r->n[1] += a->n[1];
     r->n[2] += a->n[2];
@@ -479,11 +478,9 @@ SECP256K1_INLINE static void secp256k1_fe_add(secp256k1_fe *r, const secp256k1_f
 }
 
 SECP256K1_INLINE static void secp256k1_fe_add_int(secp256k1_fe *r, int a) {
-#ifdef VERIFY
     secp256k1_fe_verify(r);
     VERIFY_CHECK(a >= 0);
     VERIFY_CHECK(a <= 0x7FFF);
-#endif
     r->n[0] += a;
 #ifdef VERIFY
     r->magnitude += 1;

src/field_5x52_impl.h

@@ -33,8 +33,8 @@
  *  0 or 1, and its value is already reduced modulo the order of the field.
  */
 
-#ifdef VERIFY
 static void secp256k1_fe_verify(const secp256k1_fe *a) {
+#ifdef VERIFY
     const uint64_t *d = a->n;
     int m = a->normalized ? 1 : 2 * a->magnitude, r = 1;
    /* secp256k1 'p' value defined in "Standards for Efficient Cryptography" (SEC2) 2.7.1. */
@@ -52,8 +52,9 @@ static void secp256k1_fe_verify(const secp256k1_fe *a) {
         }
     }
     VERIFY_CHECK(r == 1);
-}
 #endif
+    (void)a;
+}
 
 static void secp256k1_fe_get_bounds(secp256k1_fe *r, int m) {
     VERIFY_CHECK(m >= 0);
@@ -422,11 +423,9 @@ SECP256K1_INLINE static void secp256k1_fe_mul_int(secp256k1_fe *r, int a) {
 }
 
 SECP256K1_INLINE static void secp256k1_fe_add_int(secp256k1_fe *r, int a) {
-#ifdef VERIFY
     secp256k1_fe_verify(r);
     VERIFY_CHECK(a >= 0);
     VERIFY_CHECK(a <= 0x7FFF);
-#endif
     r->n[0] += a;
 #ifdef VERIFY
     r->magnitude += 1;
@@ -436,9 +435,7 @@ SECP256K1_INLINE static void secp256k1_fe_add_int(secp256k1_fe *r, int a) {
 }
 
 SECP256K1_INLINE static void secp256k1_fe_add(secp256k1_fe *r, const secp256k1_fe *a) {
-#ifdef VERIFY
     secp256k1_fe_verify(a);
-#endif
     r->n[0] += a->n[0];
     r->n[1] += a->n[1];
     r->n[2] += a->n[2];

src/group.h

@@ -164,4 +164,10 @@ static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *b);
  */
 static int secp256k1_ge_is_in_correct_subgroup(const secp256k1_ge* ge);
 
+/** 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 */

src/group_impl.h

@@ -73,35 +73,80 @@ static const secp256k1_ge secp256k1_ge_const_g = SECP256K1_G;
 #endif
 /* End of section generated by sage/gen_exhaustive_groups.sage. */
 
+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;
+}
+
+/* Set r to the affine coordinates of Jacobian point (a.x, a.y, 1/zi). */
 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);
     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;
+    secp256k1_ge_verify(r);
+}
+
+/* Set r to the affine coordinates of Jacobian point (a.x, a.y, 1/zi). */
+static void secp256k1_ge_set_ge_zinv(secp256k1_ge *r, const secp256k1_ge *a, const secp256k1_fe *zi) {
+    secp256k1_fe zi2;
+    secp256k1_fe zi3;
+    secp256k1_ge_verify(a);
+    secp256k1_fe_verify(zi);
+    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;
+    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);
@@ -111,14 +156,17 @@ 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;
-    if (a->infinity) {
+    secp256k1_gej_verify(a);
+    if (secp256k1_gej_is_infinity(a)) {
         secp256k1_ge_set_infinity(r);
         return;
     }
+    r->infinity = 0;
     secp256k1_fe_inv_var(&a->z, &a->z);
     secp256k1_fe_sqr(&z2, &a->z);
     secp256k1_fe_mul(&z3, &a->z, &z2);
@@ -126,6 +174,7 @@ 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);
+    secp256k1_ge_verify(r);
 }
 
 static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a, size_t len) {
@@ -134,6 +183,7 @@ 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) {
             secp256k1_ge_set_infinity(&r[i]);
         } else {
@@ -167,6 +217,7 @@ 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);
         }
+        secp256k1_ge_verify(&r[i]);
     }
 }
 
@@ -175,21 +226,25 @@ static void secp256k1_ge_table_set_globalz(size_t len, secp256k1_ge *a, const se
     secp256k1_fe zs;
 
     if (len > 0) {
+        /* Verify inputs a[len-1] and zr[len-1]. */
+        secp256k1_ge_verify(&a[i]);
+        secp256k1_fe_verify(&zr[i]);
         /* Ensure all y values are in weak normal form for fast negation of points */
         secp256k1_fe_normalize_weak(&a[i].y);
         zs = zr[i];
 
         /* Work our way backwards, using the z-ratios to scale the x/y values. */
         while (i > 0) {
-            secp256k1_gej tmpa;
+            /* Verify all inputs a[i] and zr[i]. */
+            secp256k1_fe_verify(&zr[i]);
+            secp256k1_ge_verify(&a[i]);
             if (i != len - 1) {
                 secp256k1_fe_mul(&zs, &zs, &zr[i]);
             }
             i--;
-            tmpa.x = a[i].x;
+            secp256k1_ge_set_ge_zinv(&a[i], &a[i], &zs);
-            tmpa.y = a[i].y;
+            /* Verify the output a[i]. */
-            tmpa.infinity = 0;
+            secp256k1_ge_verify(&a[i]);
-            secp256k1_ge_set_gej_zinv(&a[i], &tmpa, &zs);
         }
     }
 }
@@ -199,12 +254,14 @@ 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) {
@@ -222,31 +279,35 @@ 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;
+    secp256k1_fe_verify(x);
     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)) {
+    ret = secp256k1_fe_sqrt(&r->y, &x3);
-        return 0;
-    }
     secp256k1_fe_normalize_var(&r->y);
     if (secp256k1_fe_is_odd(&r->y) != odd) {
         secp256k1_fe_negate(&r->y, &r->y, 1);
     }
-    return 1;
+    secp256k1_ge_verify(r);
-
+    return ret;
 }
 
 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_var(const secp256k1_gej *a, const secp256k1_gej *b) {
     secp256k1_gej tmp;
+    secp256k1_gej_verify(b);
+    secp256k1_gej_verify(a);
     secp256k1_gej_neg(&tmp, a);
     secp256k1_gej_add_var(&tmp, &tmp, b, NULL);
     return secp256k1_gej_is_infinity(&tmp);
@@ -254,6 +315,8 @@ 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;
+    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);
@@ -261,20 +324,24 @@ 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) {
+    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_ge_is_valid_var(const secp256k1_ge *a) {
     secp256k1_fe y2, x3;
+    secp256k1_ge_verify(a);
     if (a->infinity) {
         return 0;
     }
@@ -290,6 +357,7 @@ 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;
 
+    secp256k1_gej_verify(a);
     r->infinity = a->infinity;
 
     /* Formula used:
@@ -316,6 +384,7 @@ 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) */
+    secp256k1_gej_verify(r);
 }
 
 static void secp256k1_gej_double_var(secp256k1_gej *r, const secp256k1_gej *a, secp256k1_fe *rzr) {
@@ -329,6 +398,7 @@ 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) {
@@ -343,12 +413,15 @@ static void secp256k1_gej_double_var(secp256k1_gej *r, const secp256k1_gej *a, s
     }
 
     secp256k1_gej_double(r, a);
+    secp256k1_gej_verify(r);
 }
 
 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;
 
+    secp256k1_gej_verify(a);
+    secp256k1_gej_verify(b);
     if (a->infinity) {
         VERIFY_CHECK(rzr == NULL);
         *r = *b;
@@ -403,11 +476,14 @@ 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);
+    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, 13 add/negate/normalize_weak/normalizes_to_zero (ignoring special cases) */
     secp256k1_fe z12, u1, u2, s1, s2, h, i, h2, h3, t;
+    secp256k1_gej_verify(a);
+    secp256k1_ge_verify(b);
     if (a->infinity) {
         VERIFY_CHECK(rzr == NULL);
         secp256k1_gej_set_ge(r, b);
@@ -460,12 +536,16 @@ 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);
+    secp256k1_gej_verify(r);
+    if (rzr != NULL) secp256k1_fe_verify(rzr);
 }
 
 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;
 
+    secp256k1_ge_verify(b);
+    secp256k1_fe_verify(bzinv);
     if (a->infinity) {
         secp256k1_fe bzinv2, bzinv3;
         r->infinity = b->infinity;
@@ -524,6 +604,7 @@ 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);
+    secp256k1_gej_verify(r);
 }
 
 
@@ -532,6 +613,8 @@ 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;
+    secp256k1_gej_verify(a);
+    secp256k1_ge_verify(b);
     VERIFY_CHECK(!b->infinity);
     VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
 
@@ -657,21 +740,26 @@ 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);
+    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);
@@ -685,14 +773,18 @@ 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_gej_cmov(secp256k1_gej *r, const secp256k1_gej *a, int flag) {
+    secp256k1_gej_verify(r);
+    secp256k1_gej_verify(a);
     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;
+    secp256k1_gej_verify(r);
 }
 
 static SECP256K1_INLINE void secp256k1_ge_storage_cmov(secp256k1_ge_storage *r, const secp256k1_ge_storage *a, int flag) {
@@ -702,7 +794,9 @@ 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;
+    secp256k1_ge_verify(a);
     secp256k1_fe_mul(&r->x, &r->x, &secp256k1_const_beta);
+    secp256k1_ge_verify(r);
 }
 
 static int secp256k1_ge_is_in_correct_subgroup(const secp256k1_ge* ge) {
@@ -710,6 +804,7 @@ static int secp256k1_ge_is_in_correct_subgroup(const secp256k1_ge* ge) {
     secp256k1_gej out;
     int i;
 
+    secp256k1_ge_verify(ge);
     /* A very simple EC multiplication ladder that avoids a dependency on ecmult. */
     secp256k1_gej_set_infinity(&out);
     for (i = 0; i < 32; ++i) {

src/tests_exhaustive.c

@@ -193,7 +193,7 @@ static void test_exhaustive_ecmult(const secp256k1_ge *group, const secp256k1_ge
     }
 
     for (j = 0; j < EXHAUSTIVE_TEST_ORDER; j++) {
-        for (i = 1; i < EXHAUSTIVE_TEST_ORDER; i++) {
+        for (i = 0; i < EXHAUSTIVE_TEST_ORDER; i++) {
             int ret;
             secp256k1_gej tmp;
             secp256k1_fe xn, xd, tmpf;
@@ -207,7 +207,7 @@ static void test_exhaustive_ecmult(const secp256k1_ge *group, const secp256k1_ge
             secp256k1_ecmult_const(&tmp, &group[i], &ng);
             ge_equals_gej(&group[(i * j) % EXHAUSTIVE_TEST_ORDER], &tmp);
 
-            if (j != 0) {
+            if (i != 0 && j != 0) {
                 /* Test secp256k1_ecmult_const_xonly with all curve X coordinates, and xd=NULL. */
                 ret = secp256k1_ecmult_const_xonly(&tmpf, &group[i].x, NULL, &ng, 0);
                 CHECK(ret);