Merge #16512: rpc: Shuffle inputs and outputs after joining psbts

c0b5d9710322a614a50ab5da081558cf6a38ad2a Test that joinpsbts randomly shuffles the inputs (Andrew Chow)
6f405a1d3b38395e35571b68aae55cae50e0762a Shuffle inputs and outputs after joining psbts (Andrew Chow)

Pull request description:

  `joinpsbts` currently just adds the inputs and outputs in the order of that the PSBTs were provided. This makes it extremely easy to identify which outputs belong to which inputs. This PR changes that so that all of the inputs and outputs are shuffled in the joined transaction.

ACKs for top commit:
  instagibbs:
    utACK https://github.com/bitcoin/bitcoin/pull/16512/commits/c0b5d9710322a614a50ab5da081558cf6a38ad2a
  jonatack:
    ACK c0b5d9710322a614a50ab5da081558cf6a38ad2a modulo suggestions for later.

Tree-SHA512: 14a0b7aae07d92e6d2c76a3a3b228b481e1964cb7d34f97515bdda18e2ea05a9f97c5a22affc143b86ae8b95c3cb239849fb54219d65512bc2112264dca915c8

1 files changed, 24 insertions, 1 deletions

diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index fb8ea8c227..4003299662 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -17,6 +17,7 @@
 #include <policy/rbf.h>
 #include <primitives/transaction.h>
 #include <psbt.h>
+#include <random.h>
 #include <rpc/rawtransaction_util.h>
 #include <rpc/server.h>
 #include <rpc/util.h>
@@ -1615,8 +1616,30 @@ UniValue joinpsbts(const JSONRPCRequest& request)
         merged_psbt.unknown.insert(psbt.unknown.begin(), psbt.unknown.end());
     }
 
+    // Generate list of shuffled indices for shuffling inputs and outputs of the merged PSBT
+    std::vector<int> input_indices(merged_psbt.inputs.size());
+    std::iota(input_indices.begin(), input_indices.end(), 0);
+    std::vector<int> output_indices(merged_psbt.outputs.size());
+    std::iota(output_indices.begin(), output_indices.end(), 0);
+
+    // Shuffle input and output indicies lists
+    Shuffle(input_indices.begin(), input_indices.end(), FastRandomContext());
+    Shuffle(output_indices.begin(), output_indices.end(), FastRandomContext());
+
+    PartiallySignedTransaction shuffled_psbt;
+    shuffled_psbt.tx = CMutableTransaction();
+    shuffled_psbt.tx->nVersion = merged_psbt.tx->nVersion;
+    shuffled_psbt.tx->nLockTime = merged_psbt.tx->nLockTime;
+    for (int i : input_indices) {
+        shuffled_psbt.AddInput(merged_psbt.tx->vin[i], merged_psbt.inputs[i]);
+    }
+    for (int i : output_indices) {
+        shuffled_psbt.AddOutput(merged_psbt.tx->vout[i], merged_psbt.outputs[i]);
+    }
+    shuffled_psbt.unknown.insert(merged_psbt.unknown.begin(), merged_psbt.unknown.end());
+
     CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
-    ssTx << merged_psbt;
+    ssTx << shuffled_psbt;
     return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
 }