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Are all UTXOs locked by an address spent in a transaction?

UTXO all sent to change address?Signing transactions with un/compressed keyStatic receive address instead of dynamic?Processing multiple transactions very fastWhere to find UTXO Metadata APIHow can you consolidate your personal UTXO set? (different wallet answers welcomed)what happens to UTXOs when a transaction output script is satisfied?How many change outputs are there in a Bitcoin transactionI seem to have too many unspent outputs for my given balance. What am I missing?Use UTXOs before transaction is signed/broadcasted

3

Imagine I have 2 UTXOs locked by my address, each of which allows me to spend 5 bitcoins.

If I subsequently want to send just 2 bitcoins to someone else, will both UTXOs be used as inputs in the transaction, where I now receive 8 BTC change as a single UTXO locked to my address, or as the value I want to spend can be covered by a single UTXO, is only one of the 5 BTC UTXOs spent by the transaction and I receive change in a new UTXO worth 3 BTC locked by my address. So now my address locks two UTXOs, one for 5 BTC which was not needed in this transaction, plus the change I just received for 3 BTC. Or something else?

utxo transaction-input address-reuse coin-selection

share|improve this question

edited 1 hour ago

Murch♦

35.3k27115330

asked 1 hour ago

Simon O'HanlonSimon O'Hanlon

1184

New contributor

Simon O'Hanlon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  As an aside, this question helps exemplify why address reuse is very bad for privacy: the person you pay 2 BTC to will be able to see that you control an address that holds many UTXOs, rather than just seeing the single UTXO that you spent to pay them. So with address reuse, you grant anyone you transact with the ability to see a much larger portion of your financial history.
  
  – chytrik
  18 mins ago
  
  
  

  
  
  
  

add a comment | 

3

Imagine I have 2 UTXOs locked by my address, each of which allows me to spend 5 bitcoins.

If I subsequently want to send just 2 bitcoins to someone else, will both UTXOs be used as inputs in the transaction, where I now receive 8 BTC change as a single UTXO locked to my address, or as the value I want to spend can be covered by a single UTXO, is only one of the 5 BTC UTXOs spent by the transaction and I receive change in a new UTXO worth 3 BTC locked by my address. So now my address locks two UTXOs, one for 5 BTC which was not needed in this transaction, plus the change I just received for 3 BTC. Or something else?

utxo transaction-input address-reuse coin-selection

share|improve this question

edited 1 hour ago

Murch♦

35.3k27115330

asked 1 hour ago

Simon O'HanlonSimon O'Hanlon

1184

New contributor

Simon O'Hanlon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  As an aside, this question helps exemplify why address reuse is very bad for privacy: the person you pay 2 BTC to will be able to see that you control an address that holds many UTXOs, rather than just seeing the single UTXO that you spent to pay them. So with address reuse, you grant anyone you transact with the ability to see a much larger portion of your financial history.
  
  – chytrik
  18 mins ago
  
  
  

  
  
  
  

add a comment | 

Imagine I have 2 UTXOs locked by my address, each of which allows me to spend 5 bitcoins.

If I subsequently want to send just 2 bitcoins to someone else, will both UTXOs be used as inputs in the transaction, where I now receive 8 BTC change as a single UTXO locked to my address, or as the value I want to spend can be covered by a single UTXO, is only one of the 5 BTC UTXOs spent by the transaction and I receive change in a new UTXO worth 3 BTC locked by my address. So now my address locks two UTXOs, one for 5 BTC which was not needed in this transaction, plus the change I just received for 3 BTC. Or something else?

utxo transaction-input address-reuse coin-selection

share|improve this question

edited 1 hour ago

Murch♦

35.3k27115330

asked 1 hour ago

Simon O'HanlonSimon O'Hanlon

1184

New contributor

Simon O'Hanlon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 1 hour ago

Murch♦

35.3k27115330

asked 1 hour ago

Simon O'HanlonSimon O'Hanlon

1184

New contributor

Simon O'Hanlon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 1 hour ago

Murch♦

35.3k27115330

asked 1 hour ago

Simon O'HanlonSimon O'Hanlon

1184

New contributor

Simon O'Hanlon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 1 hour ago

Murch♦

35.3k27115330

edited 1 hour ago

Murch♦

35.3k27115330

asked 1 hour ago

Simon O'HanlonSimon O'Hanlon

1184

New contributor

Simon O'Hanlon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 1 hour ago

Simon O'HanlonSimon O'Hanlon

1184

1 Answer
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3

Transactions explicitly refer to which UTXOs they are spending.

You can construct a transaction which only spends one of the two 5-BTC UTXOs, and sends 2 BTC to the destination and 3 BTC to a (possibly new) address of yourself.

You can also construct a transaction which spends both, and sends 8 BTC back to yourself. Or it could have multiple outputs that send funds back to yourself, summing up to 8 BTC.

In short: there is nothing special about the two UTXOs that share an address, apart from the fact that the same key can sign for both - but it doesn't have to.

share|improve this answer

answered 1 hour ago

Pieter WuillePieter Wuille

47.2k399158

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you for this clear explanation of the wonderful flexibility of the UTXO model.
  
  – Simon O'Hanlon
  1 hour ago
  

  
  
  
  

add a comment | 

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3

Transactions explicitly refer to which UTXOs they are spending.

You can construct a transaction which only spends one of the two 5-BTC UTXOs, and sends 2 BTC to the destination and 3 BTC to a (possibly new) address of yourself.

You can also construct a transaction which spends both, and sends 8 BTC back to yourself. Or it could have multiple outputs that send funds back to yourself, summing up to 8 BTC.

In short: there is nothing special about the two UTXOs that share an address, apart from the fact that the same key can sign for both - but it doesn't have to.

share|improve this answer

answered 1 hour ago

Pieter WuillePieter Wuille

47.2k399158

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you for this clear explanation of the wonderful flexibility of the UTXO model.
  
  – Simon O'Hanlon
  1 hour ago
  

  
  
  
  

add a comment | 

3

Transactions explicitly refer to which UTXOs they are spending.

You can construct a transaction which only spends one of the two 5-BTC UTXOs, and sends 2 BTC to the destination and 3 BTC to a (possibly new) address of yourself.

You can also construct a transaction which spends both, and sends 8 BTC back to yourself. Or it could have multiple outputs that send funds back to yourself, summing up to 8 BTC.

In short: there is nothing special about the two UTXOs that share an address, apart from the fact that the same key can sign for both - but it doesn't have to.

share|improve this answer

answered 1 hour ago

Pieter WuillePieter Wuille

47.2k399158

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you for this clear explanation of the wonderful flexibility of the UTXO model.
  
  – Simon O'Hanlon
  1 hour ago
  

  
  
  
  

add a comment | 

Transactions explicitly refer to which UTXOs they are spending.

You can construct a transaction which only spends one of the two 5-BTC UTXOs, and sends 2 BTC to the destination and 3 BTC to a (possibly new) address of yourself.

You can also construct a transaction which spends both, and sends 8 BTC back to yourself. Or it could have multiple outputs that send funds back to yourself, summing up to 8 BTC.

In short: there is nothing special about the two UTXOs that share an address, apart from the fact that the same key can sign for both - but it doesn't have to.

share|improve this answer

answered 1 hour ago

Pieter WuillePieter Wuille

47.2k399158

share|improve this answer

answered 1 hour ago

Pieter WuillePieter Wuille

47.2k399158

answered 1 hour ago

Pieter WuillePieter Wuille

47.2k399158

answered 1 hour ago

Pieter WuillePieter Wuille

47.2k399158