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[wallet] randomly generate change targets

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If the wallet always chooses 1 million sats as its change target, it is
easier to fingerprint transactions created by the Core wallet.
This commit is contained in:
glozow
2022-03-07 13:46:49 +00:00
parent 1e52e6bd0a
commit a44236addd
4 changed files with 47 additions and 4 deletions
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11
src/wallet/spend.cpp
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@@ -19,6 +19,8 @@
#include <wallet/transaction.h>
#include <wallet/wallet.h>
#include <cmath>
using interfaces::FoundBlock;
namespace wallet {
@@ -395,9 +397,11 @@ std::optional<SelectionResult> AttemptSelection(const CWallet& wallet, const CAm
results.push_back(*knapsack_result);
}
// We include the minimum final change for SRD as we do want to avoid making really small change.
// KnapsackSolver does not need this because it includes MIN_CHANGE internally.
const CAmount srd_target = nTargetValue + coin_selection_params.m_change_fee + MIN_FINAL_CHANGE;
// Include change for SRD as we want to avoid making really small change if the selection just
// barely meets the target. Just use the lower bound change target instead of the randomly
// generated one, since SRD will result in a random change amount anyway; avoid making the
// target needlessly large.
const CAmount srd_target = nTargetValue + coin_selection_params.m_change_fee + CHANGE_LOWER;
if (auto srd_result{SelectCoinsSRD(positive_groups, srd_target, coin_selection_params.rng_fast)}) {
srd_result->ComputeAndSetWaste(coin_selection_params.m_cost_of_change);
results.push_back(*srd_result);
@@ -681,6 +685,7 @@ static bool CreateTransactionInternal(
coin_selection_params.m_subtract_fee_outputs = true;
}
}
coin_selection_params.m_change_target = GenerateChangeTarget(std::floor(recipients_sum / vecSend.size()), rng_fast);
// Create change script that will be used if we need change
CScript scriptChange;