Difference between revisions of "NLockTime"

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(Correct the BIP68 additions)
(Clarify that nLockTime cannot equal to the height of the block in which it is mined, and that the MTP is based on prior blocks only.)
 
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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.
  
 +
* If <code>nLockTime < 500000000</code>
 +
** Specifies the block number after which this transaction can be included in a block.
 +
* Otherwise
 +
** Specifies the UNIX timestamp after which this transaction can be included in a block.
  
Since [https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki BIP68], the '''nLockTime''' can specify a relative lock time. Given a transaction,
+
Note that since the adoption of BIP 113, the time-based nLockTime is compared to the 11-block [[median time past]] (the median timestamp of the 11 blocks preceding the block in which the transaction is mined), and not the block time itself. The median time past tends to lag the current unix time by about one hour (give or take), but unlike block time it increases monotonically.
* If the most significant bit (1<<31) is not set
+
 
** If the 23rd bit (1<<22) is set
+
For transaction relay, nLockTime must be <= the current block's height (block-based) or <= the current median time past (if time based). This ensures that the transaction can be included in the next block.
*** 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>.
 
** 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 <code>spending_tx_block_height > spent_tx_block_height + nLockTime</code>
 
* Otherwise
 
** the transaction can be included in any block
 
  
 
==See Also==
 
==See Also==
 
* lock_time in [[Protocol_specification#tx|the protocol specification]]
 
* lock_time in [[Protocol_specification#tx|the protocol specification]]
 
* [[Timelock]]
 
* [[Timelock]]
* [https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki BIP68]
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* [https://github.com/bitcoin/bips/blob/master/bip-0113.mediawiki BIP113]
 
* The CHECKLOCKTIMEVERIFY opcode in [https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki BIP65]
 
* The CHECKLOCKTIMEVERIFY opcode in [https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki BIP65]
* The CHECKSEQUENCEVERIFY opcode in [https://github.com/bitcoin/bips/blob/master/bip-00112.mediawiki BIP112]
 
  
 
[[Category:Technical]]
 
[[Category:Technical]]
 
{{lowercase}}
 
{{lowercase}}

Latest revision as of 16:15, 6 November 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.

  • If nLockTime < 500000000
    • Specifies the block number after which this transaction can be included in a block.
  • Otherwise
    • Specifies the UNIX timestamp after which this transaction can be included in a block.

Note that since the adoption of BIP 113, the time-based nLockTime is compared to the 11-block median time past (the median timestamp of the 11 blocks preceding the block in which the transaction is mined), and not the block time itself. The median time past tends to lag the current unix time by about one hour (give or take), but unlike block time it increases monotonically.

For transaction relay, nLockTime must be <= the current block's height (block-based) or <= the current median time past (if time based). This ensures that the transaction can be included in the next block.

See Also