Timelock/Locktime

What Is a Timelock/Locktime?

A timelock/locktime is a requirement for a transaction to be completed only at a specific time or block on the blockchain. Timelock can be thought of as a schedule by which miners on the blockchain process cryptocurrency transactions. Transactions will be added in the Merkle Tree depending on the block height allowed by miners. Transactions are only allowed after this step is completed.

Diving Deep Into the Concept of a Timelock/Locktime

Satoshi Nakamoto, the creator of the cryptocurrency Bitcoin, was the first to include timelocks. The goal was for this to appear in all transactions. The blocking time is set to 0x00000000 by default (0). 

Timelocks prevent transactions from being confirmed until a specific time, or block height is achieved. Timelocks can be absolute or relative in nature. Absolute timelocks guarantee that blocks are defined in relation to a specific time. 

Time-relative timelocks are used to specify how much time must pass until transactions can be validated. In Bitcoin transactions, time may be quantified in two ways. These are based on the block number and timestamp of the transaction. 

Once a timelock is established based on a block number, miners will acquire a specific block number. Miners must wait until the specified time period has passed before verifying the transaction for timelocks based on timestamps.

Ways To Determine Timelocks

There are four methods for determining Bitcoin timelocks. The transaction level accounts for half of these, whereas the script level accounts for the other half.

• nLockTime: nLockTime entails transaction-level absolute blocking.

• nSequence: A timelock in relation to transaction levels is a nSequence.

• CheckLockTimeVerify: At the script level, CheckLockTimeVerify includes absolute time blocking.

• CheckSquenceVerify: CheckSquenceVerify is a relative time lock at the script level.