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What order does Bitcoin core place the inputs it spends in? Is it random? Is it sorted by anything? What, if anything, can you tell about the originator of a transaction by the input ordering?
What order does Bitcoin Core place the inputs it spends in?
Answers
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The inputs are chosen by the function SelectCoins() in CreateTransaction() and then added one by one (without shuffling) to the transaction.
The order is defined by the coin selection (CWallet::SelectCoinsMinConf) which does a random shuffle of the potential useful inputs and a stochastic approximation.
Mind also that Bitcoin-Core's coin selection could be improved and there are several issues and improve proposals ([1], [2], [3])
related: What is the coin selection algorithm?
– Murch – 2015-08-13T10:26:56.460