 There have been many countermeasures designed for pinning attacks. So this isn't the first, it will be the last and this is a kind of an arms race of technologies essentially. So first of all, what is RBF? RBF is replaced by fee and it is a feature that allows you to bump the fee in your transaction by replacing it with essentially double-spending transaction that increases the fee. You mark your original transaction as RBF and that tells all nodes, hey, you may see a replacement transaction intended to increase the fee and if so, please replace it with the intended transaction. Something that miners will do anyway because it's in their interest to earn more fee so they will do that, but it also signals to other nodes that this is likely to happen. And pinning attacks don't only apply to RBF, they apply to many other types of transaction chaining or transaction fee-increasing situations. So you have RBF pinning, you have CPFP pinning which is child-pace for parent pinning, you have lightning pinning attacks and the pinning attack is basically where you don't let someone get a transaction into the blockchain by bogging them down essentially or by taking advantage of various controls that exist to prevent spam and denial of service attacks to pin the current transaction, that's what's called the pinning attack, to pin the current version of the transaction as is in the mempool and not let it be replaced by a different transaction. Here's why you might wanna do this. Let's say you've got a Lightning Network channel closure and someone's trying to implement a penalty transaction and fees are really high and you want to prevent them from getting that transaction accepted or you want to jam a transaction and leave it pending unconfirmed for whatever reason. And so you can do that by using a pinning attack. For example, as I said, RBF is a technology where you can replace one transaction with another transaction that spends a greater fee that way you bump the fee, replaced by fee. The way the mempool protects from several other types of denial of service attacks is it looks at the absolute fee rather than the fee rate when deciding whether to replace it. And so if you are able to create an RBF transaction that creates an impossibly huge fee, then you're pinning that instead of the transaction that they're trying to create to bump the original one. You can do that also with CPFP where you have essentially two outputs. One is change, one is payment. And that means that either party, the person who owns the change or the person who owns the recipient of the payment can create a child or several children. Well, there are limits to how many children you can create. So if one person creates a thousand children transactions, they can push into that limit so as to prevent you from creating a child transaction that would bump the fee. They're essentially just taking advantage of anti-spam measures. There are constant back and forth moves here and changes to, for example, Bitcoin Core Software and how it treats the mempool to make it difficult to pin transactions because this is a form of censorship or at least it achieves the same result, a censorship that prevents someone from executing a transaction but within the rules of the network. So it's exploiting the rules of the network. And this is something you've heard me say before, perhaps when people ask, why can't we stop spam on the network? Why can't we stop ordinals? Why can't we stop whatever other application we don't like from happening on the network? And the reason is exactly this, which is that when you put rules into the software that starts limiting aspects of the transaction, those rules can then be exploited by people who run up to those limits and use them to jam the network in a different way. One person's remedy as another person's attack vector is one way to put it. It's one of the reasons why censorship resistance and denial of service are almost like a trade-off. If you want to have very low censorship, very high censorship resistance, very low censorship, you wanna make it so that people can make their transactions, then the result is that people can also do denial of service or spam attacks or jam the network and increase fees. If you try to stop them from spamming the network and creating denial of service attacks, then you're also gonna prevent people from making legitimate transactions because you open up another attack vector. I hope you enjoyed that video. If you'd like to support me in my mission of educating people about Bitcoin and open blockchains all around the world and publishing free content under Creative Commons licenses, please consider subscribing to the channel, sharing this video, as well as supporting me on patreon.com slash a-a-n-t-o-n-o-p. Thank you.