Difference between revisions of "NLockTime"

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(Updated the page to reflect the actual consensus meaning of the `nLockTime` field.)
(Add more details about the lock time interpretation.)
 
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'''nLockTime''' is a parameter of a transaction, that, if any input indicates so (by having nSequence not equal to UINT_MAX), mandates a minimal time (specified in either unix time or block height), before which the transaction cannot be accepted into a block.  If all inputs in a transaction have nSequence equal to UINT_MAX, then nLockTime is ignored.
 
'''nLockTime''' is a parameter of a transaction, that, if any input indicates so (by having nSequence not equal to UINT_MAX), mandates a minimal time (specified in either unix time or block height), before which the transaction cannot be accepted into a block.  If all inputs in a transaction have nSequence equal to UINT_MAX, then nLockTime is ignored.
  
 
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Since [https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki BIP68], the lock time can either be absolute or relative. Given a transaction,
Since [https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki BIP68], a new meaning has been given to the '''nLockTime''' and '''nSequence''' fields. Given a transaction,
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* If the most significant bit (<code>1<<31</code>) of the '''nLockTime''' field is set (if the lock time is absolute)
* If the most significant bit (1<<31) is set
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** If <code>nLockTime < 500000000</code>
** If the 23rd bit (1<<22) is set
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*** Specifies the block number at which this transaction can be spent
*** Specifies a time in units of 512 seconds. The transaction can only be included in a block if <code>block_time > nLockTime * 512</code>.
 
 
** Otherwise
 
** Otherwise
*** Specifies a block height before which the transaction can not be included in a block.
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*** Specifies the UNIX timestamp at which this transaction can be spent
* Otherwise
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* Otherwise (if the lock time is relative)
** the transaction can be included in any block
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** If the 23rd bit (<code>1<<22</code>) is not set
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*** The last 16 bits of the '''nLockTime''' field specify a relative time in units of 512 seconds. The transaction can only be included in a block if <code>spending_tx_block_time > spent_tx_block_time + nLockTime * 512</code>.
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** Otherwise
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*** The last 16 bits of the '''nLockTime''' field specify a relative block height before which the transaction can not be included in a block. In other words it can be included if <code>spending_tx_block_height > spent_tx_block_height + nLockTime</code>
  
 
==See Also==
 
==See Also==

Latest revision as of 13:00, 23 September 2019

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nLockTime is a parameter of a transaction, that, if any input indicates so (by having nSequence not equal to UINT_MAX), mandates a minimal time (specified in either unix time or block height), before which the transaction cannot be accepted into a block. If all inputs in a transaction have nSequence equal to UINT_MAX, then nLockTime is ignored.

Since BIP68, the lock time can either be absolute or relative. Given a transaction,

  • If the most significant bit (1<<31) of the nLockTime field is set (if the lock time is absolute)
    • If nLockTime < 500000000
      • Specifies the block number at which this transaction can be spent
    • Otherwise
      • Specifies the UNIX timestamp at which this transaction can be spent
  • Otherwise (if the lock time is relative)
    • If the 23rd bit (1<<22) is not set
      • The last 16 bits of the nLockTime field specify a relative time in units of 512 seconds. The transaction can only be included in a block if spending_tx_block_time > spent_tx_block_time + nLockTime * 512.
    • Otherwise
      • The last 16 bits of the nLockTime field specify a relative block height before which the transaction can not be included in a block. In other words it can be included if spending_tx_block_height > spent_tx_block_height + nLockTime

See Also