# Op\_checkmaxtimeverify

**URL:** <https://delvingbitcoin.org/t/op-checkmaxtimeverify/581>\
**Category:** Protocol Design\
**Tags:** softfork\
**Created:** [February 18, 2024, 2:30am UTC](https://delvingbitcoin.org/t/op-checkmaxtimeverify/581 "2024-02-18T02:30:05Z")\
**Posts on this page:** 1\
**Showing post:** 8

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**Author:** ![murch](https://delvingbitcoin.org/user_avatar/delvingbitcoin.org/murch/32/139_2.png) [@murch](https://delvingbitcoin.org/u/murch)\
**Post date:** [March 12, 2024, 8:05pm UTC](https://delvingbitcoin.org/t/op-checkmaxtimeverify/581/8 "2024-03-12T20:05:54Z")

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> [@EvanWinget](#):
>
> Thanks for the thoughtful response and all of the work you have been doing for so many years to help educate Bitcoiners and improve Bitcoin.

Cheers, thanks!

> [@EvanWinget](#):
>
> it would take extremely high fees for expiring transactions to create incentives to reorg compared to working on the next block

Fees of expiring transactions creating an incentive for reorging the previous block to include them sounds indeed not particularly problematic to me: if their fees had been high enough to warrant that, they should have been included in the block in the first place. Rather, I meant the opposite: a transaction for a substantial amount is confirmed in the ultimate block in which it is permitted, and a miner collaborating with the sender reorganizes that block out to cancel the payment. In that case, rather than just the transaction fees providing an incentive, the attack’s reward could be up to the payment amount.

> [@EvanWinget](#):
>
> nodes should require higher minimum relay fees for transactions close to their expiration height to ensure we don’t waste bandwidth on transactions that have no potential to be mined

This seems insufficient to solve the problem, unless the premium is so high that it virtually guarantees that the transaction will be mined before it expires. However, if the feerate were that high, wouldn’t OP\_EXPIRE simply waste blockspace? If however the feerate of the transaction is merely competitive, the presence of OP\_EXPIRE creates a bandwidth-wasting vector: an attacker would submit e.g. OP\_EXPIRE transactions at the bottom of the top block and push them out of the top block with further OP\_EXPIRE transactions. This way the attacker could issue a constant stream of transactions, but never pay for more than a couple barely sliding in at the bottom of the block.

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_[View the full topic](https://delvingbitcoin.org/t/op-checkmaxtimeverify/581)._