RPC changes

The RPC `joinpsbts` will shuffle the order of the inputs and outputs of the resulting joined psbt.

Previously inputs and outputs were added in the order that the PSBTs were provided which makes correlating inputs to outputs extremely easy.

#include <random.h>

// 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());

ssTx << shuffled_psbt;