My understanding is that a transaction is a transfer of value between Bitcoin wallets that gets later included in the block chain. So a Bitcoin transaction is used only once in my understanding.

  • Can you explain what you mean by the word "used", and what has led you to the idea that a transaction could be "used" multiple times? – Nate Eldredge Feb 16 '17 at 20:25
  • I am currently writing a bachelor thesis and my supervisor told me that "A transaction might be used for a criminal purpose once during its lifetime but for "clean" uses later on. " – Aqqqq Feb 16 '17 at 20:28
  • @Aqqqq: Find (or ask your supervisor for) a better word than "transaction". A transaction is something that happens once. Consider buying an apple at the grocery store. When you hand over your €1 and get change, that's a transaction. It happened once, that same transaction never happens again. If your €1 coin gets given to somebody else as change for a €9 box of chocolates, that's an entirely different transaction. If your €1 coin is then stolen and used to buy beer, that's a different transaction again. – Greg Hewgill Feb 16 '17 at 22:25
  • possible duplicate of What is an “unspent output”? – Murch Feb 26 '17 at 7:49

What is spent it's not the transaction itself, but the outputs the transaction has created. A transaction can have multiple outputs with different bitcoin amount hold on each one.

Therefore, a transaction can be "used", in the sense you expressed it, as many times as outputs it has.

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  • I think I understood your answer. Am I correct that an example would be: Person A pays Person B and C 100 Bitcoin with a single transaction, then the transaction is used twice? – Aqqqq Feb 16 '17 at 20:41
  • Also what about input? – Aqqqq Feb 16 '17 at 20:42
  • Yes, sort of, but you should change your point of view. What is "used" is the output, not the transaction. You can see a transaction like a collection of multiple inputs and outputs. Every input is a reference to a previous transaction and a specific output that will be spent, and every output encodes its own redeem conditions. Normally, in the most common Bitcoin transactions (P2PKH), the conditions imply that the redeemer need to prove the ownership of the destination Bitcoin address, that is done by creating a digital signature. – sr-gi Feb 16 '17 at 21:29

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