Add sanity check after key generation

Add a sanity check to prevent cosmic rays from flipping a bit in the
generated public key, or bugs in the elliptic curve code. This is
simply done by signing a (randomized) message, and verifying the
result.

src/rpcdump.cpp

@@ -112,6 +112,7 @@ Value importprivkey(const Array& params, bool fHelp)
     if (!key.IsValid()) throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Private key outside allowed range");
 
     CPubKey pubkey = key.GetPubKey();
+    assert(key.VerifyPubKey(pubkey));
     CKeyID vchAddress = pubkey.GetID();
     {
         pwalletMain->MarkDirty();
@@ -253,6 +254,7 @@ Value importwallet(const Array& params, bool fHelp)
             continue;
         CKey key = vchSecret.GetKey();
         CPubKey pubkey = key.GetPubKey();
+        assert(key.VerifyPubKey(pubkey));
         CKeyID keyid = pubkey.GetID();
         if (pwalletMain->HaveKey(keyid)) {
             LogPrintf("Skipping import of %s (key already present)\n", CBitcoinAddress(keyid).ToString());