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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/coinselection.cpp
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@ -398,6 +398,17 @@ CAmount GetSelectionWaste(const std::set<COutput>& inputs, CAmount change_cost,
return waste;
}
CAmount GenerateChangeTarget(CAmount payment_value, FastRandomContext& rng)
{
if (payment_value <= CHANGE_LOWER / 2) {
return CHANGE_LOWER;
} else {
// random value between 50ksat and min (payment_value * 2, 1milsat)
const auto upper_bound = std::min(payment_value * 2, CHANGE_UPPER);
return rng.randrange(upper_bound - CHANGE_LOWER) + CHANGE_LOWER;
}
}
void SelectionResult::ComputeAndSetWaste(CAmount change_cost)
{
m_waste = GetSelectionWaste(m_selected_inputs, change_cost, m_target, m_use_effective);