Merge #674: [rpc]blindrawtransaction accepts more commitments

d584b65 [test]decrese num of inputs on partial blind test (Akio Nakamura)
254b166 [rpc]blindrawtransaction accepts more commitments (Akio Nakamura)

Pull request description:

  In #510 / #550 a requirement that the blinding commitments were equal in amount to the inputs was introduced. This requirement is correct for the final case, but not for partial transactions (e.g. where party 1 blinds their inputs before even handing the transaction over to party 2 to add theirs). In order to hide party 1's input amounts from party 2, blindrawtransaction must allow >= the inputs, since the commitments are shared beforehand (if not, the blinding fails; this may need further investigating).

  This PR restores the functionality to allow blinding commitments more than or equal to the amount of inputs, which makes the confidential assets demo https://github.com/ElementsProject/confidential-assets-demo functional again.

Tree-SHA512: 11c7e1c648aea26be2f4cb47606cd8e9b40d9e0d736a7eeb1989d6fad10f8f06528fd90766cb95e304c9b2c371278b20d7ef61099cb8b6e18b281a260e5de92d

src/wallet/rpcwallet.cpp

@@ -5759,8 +5759,8 @@ UniValue blindrawtransaction(const JSONRPCRequest& request)
     std::vector<std::vector<unsigned char> > auxiliary_generators;
     if (request.params.size() > 2) {
         UniValue assetCommitments = request.params[2].get_array();
-        if (assetCommitments.size() != 0 && assetCommitments.size() != tx.vin.size()) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Asset commitment array must have exactly as many entries as transaction inputs.");
+        if (assetCommitments.size() != 0 && assetCommitments.size() < tx.vin.size()) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Asset commitment array must have at least as many entries as transaction inputs.");
         }
         for (size_t nIn = 0; nIn < assetCommitments.size(); nIn++) {
             if (assetCommitments[nIn].isStr()) {

test/functional/feature_confidential_transactions.py

@@ -496,11 +496,11 @@ def run_test(self):
 
         # Create one part of the transaction to partially blind
         rawtx = self.nodes[0].createrawtransaction(
-            inputs, {dst_addr2: Decimal("0.01")})
+            inputs[:1], {dst_addr2: Decimal("0.01")})
 
         # Create another part of the transaction to partially blind
         rawtx2 = self.nodes[0].createrawtransaction(
-            inputs,
+            inputs[1:],
             {dst_addr: Decimal("0.1"), dst_addr3: Decimal("1.0")},
             0,
             False,
@@ -523,13 +523,13 @@ def run_test(self):
         # Combine the transactions
 
         # Blinded, but incomplete transaction.
-        # 3 inputs and 1 output, but no fee output, and
+        # 1 inputs and 1 output, but no fee output, and
         # it was blinded with 3 asset commitments, that means
         # the final transaction should have 3 inputs.
         btx = CTransaction()
         btx.deserialize(io.BytesIO(hex_str_to_bytes(blindtx)))
 
-        # Unblinded transaction, with 3 inputs and 2 outputs.
+        # Unblinded transaction, with 2 inputs and 2 outputs.
         # We will add them to the other transaction to make it complete.
         ubtx = CTransaction()
         ubtx.deserialize(io.BytesIO(hex_str_to_bytes(rawtx2)))
@@ -538,9 +538,11 @@ def run_test(self):
         # on top of inputs and outputs of the blinded, but incomplete transaction.
         # We also append empty witness instances to make witness arrays match
         # vin/vout arrays
+        btx.vin.append(ubtx.vin[0])
         btx.wit.vtxinwit.append(CTxInWitness())
         btx.vout.append(ubtx.vout[0])
         btx.wit.vtxoutwit.append(CTxOutWitness())
+        btx.vin.append(ubtx.vin[1])
         btx.wit.vtxinwit.append(CTxInWitness())
         btx.vout.append(ubtx.vout[1])
         btx.wit.vtxoutwit.append(CTxOutWitness())