What can you choose with Coin Control in a Bitcoin wallet?
Correct answer
Answer C: Which UTXOs you use for the payment.
Quick explanation
Your balance consists of different amounts of bitcoin you received earlier. Coin Control lets you choose which of them to spend. These parts are called UTXOs.
Detailed explanation
A wallet often controls several UTXOs from different payments. An algorithm normally selects suitable inputs. Coin control lets users specifically select, exclude or keep UTXOs separate. Selection affects virtual transaction size, fees and the amount of any change output.
Using several UTXOs together as inputs can suggest to observers that the same wallet or person controls them. Coin control can avoid unnecessarily linking UTXOs from different contexts. Wallets often use a new internal change address, but amounts and transaction patterns may still identify a suspected change output.
Privacy can also be lost later. If a previously separated change UTXO is combined with others, new visible links appear. Hasty consolidation of many small UTXOs can also connect different contexts. Conversely, very small UTXOs can be economically difficult to spend when fees are high.
Manually setting a change address is particularly risky: it must demonstrably be controlled by one's own wallet. A new address prevents reuse but does not remove all analysis heuristics. Coin control is therefore a planning tool, not an automatic fee or privacy guarantee.
Example or everyday application
A wallet controls one UTXO from a public donation address and another from a private payment context. Coin control prevents both appearing together as inputs. The resulting change UTXO must also be handled separately later; careless merging could undo the intended separation.
Key takeaway
Coin control affects inputs and change, not automatically complete privacy.
Sources used
Bitcoin Core - CCoinControl Class Reference
This source is mainly intended for developers. The relevant information may therefore be harder to find.
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