Allow dumpblinding key to accept non-CT address

This facilitates the following workflow:
1) Obtain an updated psbt with in_witness_utxo and in_utxo_rangeproof
2) Get the blinding key from the input utxo address obtained from input
script pubkey without revealing master blinding key
3) Rewind the proof to obtain blinding factors and implement stateless
blinding

src/wallet/rpcdump.cpp

@@ -2113,6 +2113,7 @@ RPCHelpMan dumpblindingkey()
 {
     return RPCHelpMan{"dumpblindingkey",
                 "\nDumps the private blinding key for a CT address in hex.",
+                "\nNote: If the address is not a CT address, looks for blinding key corresponding to this non-CT address.",
                 {
                     {"address", RPCArg::Type::STR, RPCArg::Optional::NO, "The CT address"},
                 },
@@ -2142,9 +2143,10 @@ RPCHelpMan dumpblindingkey()
     key = pwallet->GetBlindingKey(&script);
     if (key.IsValid()) {
         CPubKey pubkey(key.GetPubKey());
-        if (pubkey == GetDestinationBlindingKey(dest)) {
-            return HexStr(Span<const unsigned char>(key.begin(), key.size()));
+        if (IsBlindDestination(dest) && pubkey != GetDestinationBlindingKey(dest)) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "CT address blinding key does not match the blinding key in wallet");
         }
+        return HexStr(Span<const unsigned char>(key.begin(), key.size()));
     }
 
     throw JSONRPCError(RPC_WALLET_ERROR, "Blinding key for address is unknown");

test/functional/feature_confidential_transactions.py

@@ -272,6 +272,11 @@ def run_test(self):
 
         # Import the blinding key
         blindingkey = self.nodes[2].dumpblindingkey(address2)
+
+        # Check that importing keys from non-CT address works as intended
+        blindingkey2 = self.nodes[2].dumpblindingkey(unconfidential_address2)
+        assert_equal(blindingkey, blindingkey2)
+
         self.nodes[1].importblindingkey(address2, blindingkey)
         # Check the auditor's gettransaction and listreceivedbyaddress
         # Needs rescan to update wallet txns