Auto merge of #3390 - arcalinea:3319_discard_sk_if_invalid_ivk, r=str4d

Discard sk if ivk == 0

Addresses #3319

src/zcash/Address.cpp

@@ -67,8 +67,19 @@ SaplingIncomingViewingKey SaplingFullViewingKey::in_viewing_key() const {
     return SaplingIncomingViewingKey(ivk);
 }
 
+bool SaplingFullViewingKey::is_valid() const {
+    uint256 ivk;
+    librustzcash_crh_ivk(ak.begin(), nk.begin(), ivk.begin());
+    return !ivk.IsNull();
+}
+
 SaplingSpendingKey SaplingSpendingKey::random() {
-    return SaplingSpendingKey(random_uint256());
+    while (true) {
+        auto sk = SaplingSpendingKey(random_uint256());
+        if (sk.full_viewing_key().is_valid()) {
+            return sk;
+        }
+    }
 }
 
 boost::optional<SaplingPaymentAddress> SaplingIncomingViewingKey::address(diversifier_t d) const {
@@ -90,7 +101,6 @@ SaplingPaymentAddress SaplingSpendingKey::default_address() const {
 
 }
 
-
 bool IsValidPaymentAddress(const libzcash::PaymentAddress& zaddr) {
     return zaddr.which() != 0;
 }

src/zcash/Address.hpp

@@ -153,6 +153,7 @@ public:
     }
 
     SaplingIncomingViewingKey in_viewing_key() const;
+    bool is_valid() const;
 
     friend inline bool operator==(const SaplingFullViewingKey& a, const SaplingFullViewingKey& b) {
         return a.ak == b.ak && a.nk == b.nk && a.ovk == b.ovk;