Bitcoin: How was the relative lock time for this transaction met?

Understanding Bitcoin Transaction Locktime

As a Bitcoin user, understanding the nuances of transaction locktime is crucial for grasping how transactions are verified and processed on the blockchain. In this article, we’ll delve into the specifics of how a given transaction was satisfied with its relative locktime.

Transaction Breakdown

Let’s analyze the provided transaction: 3c1c9fb9d6b215efdeedb5caf6a951a9e6c6c1e3de6e5674f646c63e94667497. This transaction involves three inputs, which we’ll refer to as “1” and “2”. The output of the first input is labeled as “3”, while the second input is referred to as “32”.

OP_PUSHBYTES

The first few lines of the transaction are OP_PUSHBYTES_3 fa0140, followed by OP_CSV. These commands indicate that we’re about to push a byte string (the value 0x4001fa) and then calculate the checksum (OP_CSV) for it.

OP_DROP

Next, the transaction performs an OP_DROP command, which indicates that the previously calculated checksum is being dropped. This is done so that the subsequent calculations can be performed without having to recompute the checksum.

Relative Locktime Satisfaction

Now, let’s focus on satisfying the relative locktime for this transaction. Relative locktime refers to the time interval between two consecutive transactions that share a common input. In other words, if transaction A has an input with value X and transaction B shares the same input, then the relative locktime of transaction B would be the difference between their input values.

For our given transaction:

  • Input 1 (with value 0x4001fa) is shared by both transactions.

  • Output of Transaction A is output 3, while output of Transaction B is labeled as “32”.

To satisfy relative locktime for this transaction, we need to ensure that the difference between input values ​​does not exceed a certain threshold. In Bitcoin’s context, the default value for input validation is set to nSequence = 0x4001fa, which means the transaction will only be considered valid if the input value exactly matches the input used in the previous transaction (in this case, Transaction A).

However, since both inputs have the same value (0x4001fa), and we’ve already dropped the checksum, it’s unlikely that the transaction will be validated. In practice, Bitcoin uses a more robust validation mechanism involving multiple checks, including the OP_CHECKMINT command.

Conclusion

In summary, to satisfy relative locktime for this specific transaction, the input values ​​must match exactly between consecutive transactions that share a common input. Since both inputs have the same value (0x4001fa), the difference in input values ​​is unlikely to be significant enough to trigger validation checks. Nevertheless, this provides insight into how Bitcoin’s locking mechanisms work and highlights the importance of carefully examining transaction inputs when verifying their relative locktime.

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