normalize y^2 in pubkey validation

fix last commit

ecdsa.c

@@ -459,7 +459,7 @@ int ecdsa_read_pubkey(const uint8_t *pub_key, curve_point *pub)
 	if (pub_key[0] == 0x04) {
 		bn_read_be(pub_key + 1, &(pub->x));
 		bn_read_be(pub_key + 33, &(pub->y));
-#ifdef USE_PUBKEY_VALIDATE
+#if USE_PUBKEY_VALIDATE
 		return ecdsa_validate_pubkey(pub);
 #else
 		return 1;
@@ -468,7 +468,7 @@ int ecdsa_read_pubkey(const uint8_t *pub_key, curve_point *pub)
 	if (pub_key[0] == 0x02 || pub_key[0] == 0x03) { // compute missing y coords
 		bn_read_be(pub_key + 1, &(pub->x));
 		uncompress_coords(pub_key[0], &(pub->x), &(pub->y));
-#ifdef USE_PUBKEY_VALIDATE
+#if USE_PUBKEY_VALIDATE
 		return ecdsa_validate_pubkey(pub);
 #else
 		return 1;
@@ -502,6 +502,8 @@ int ecdsa_validate_pubkey(const curve_point *pub)
 
 	// y^2
 	bn_multiply(&(pub->y), &y_2, &prime256k1);
+	bn_mod(&y_2, &prime256k1);
+
 	// x^3 + b
 	bn_multiply(&(pub->x), &x_3_b, &prime256k1);
 	bn_multiply(&(pub->x), &x_3_b, &prime256k1);
@@ -542,7 +544,6 @@ int ecdsa_verify_double(const uint8_t *pub_key, const uint8_t *sig, const uint8_
 }
 
 // returns 0 if verification succeeded
-// it is assumed that public key is valid otherwise calling this does not make much sense
 int ecdsa_verify_digest(const uint8_t *pub_key, const uint8_t *sig, const uint8_t *digest)
 {
 	int i, j;

tests.c

@@ -887,7 +887,7 @@ START_TEST(test_pubkey_validity)
 	res = ecdsa_read_pubkey(pub_key, &pub);
 	ck_assert_int_eq(res, 1);
 
-#ifdef USE_PUBKEY_VALIDATE
+#if USE_PUBKEY_VALIDATE
 	memcpy(pub_key, fromhex("04f80490839af36d13701ec3f9eebdac901b51c362119d74553a3c537faff31b17e2a59ebddbdac9e87b816307a7ed5b826b8f40b92719086238e1bebf00000000"), 65);
 	res = ecdsa_read_pubkey(pub_key, &pub);
 	ck_assert_int_eq(res, 0);