TL;DR; I'm introducing Watch Swaps, a service similar to the Liquidity Swaps, but instead of opening channels to each other, node operators will watch each other's nodes with their watchtower services to protect against malicious channel force closure attacks, and the resulting potential loss of funds.

LN+'s first feature, the Liquidity Swaps have been very successful in the last year or so. More than 12K liquidity swaps allowed Bitcoin lightning network node users to cooperate with each other and open 40K channels in a mutually beneficial and efficient way. Liquidity swaps weren't only beneficial to individual node operators but to the network as a whole as well, because together we managed to decentralize the network. LN became highly resilient to single large nodes dropping out or behaving in an unfriendly way. A good test for this was when recently the second largest node (zerofeerouting) in the network dropped out. There was virtually no interruption to payments thanks to the many other nodes and their channels that could be used to route around the missing node.

Today, LN+ is launching a new feature that will hopefully improve another aspect of the network: security of your funds. We do this with the help of watchtowers to keep your channels safe even when your node is offline.

LN watchtowers are nothing new to LN+. We've been running an altruistic watchtower for a long time with the help of Voltage.cloud, but the reality is that this is a centralized solution and it's challenging to keep the server running smooth due to the huge demand.

The new LN+ Watch Swaps will allow node operators to find each other so they can watch each other's nodes using their watchtower services. With this setup, without a centralized watchtower service, even if your node is offline and somebody attacks one of your channels, the watchtower service of your choosing that nobody knows about will act on your behalf and issue a punish transaction that will send the entire capacity of the channel to your node.

Besides the obvious benefit to individual nodes, running many watchtowers is beneficial to the entire network as a whole as well. When watchtowers are common, it becomes highly risky for an attacker to maliciously force close on a channel. Due to game theory, even nodes that have no watchtowers will be safe. There will be less attacks, which in turn helps the reputation of LN in general.

Watch Swaps are rather simple. It's an agreement between two participants: the author, who starts the watch swap, and the applicant, who applies to the watch swap.

The author can start a watch swap and setup the rules, such as type of watchtower (LND Watchtower or The Eye of Satoshi for CLN), the duration, and other unique rules they may have. The size of the watch swap is set automatically based on the author's node's size expessed as an LN+ rank.

As a side node, if you notice your LN+ node rank dropping a bit, that's nothing personal against you. It's expected across the board for many nodes starting now. It's a result of a new formula to calculate the rank, which hopes to help estimate the load a certain node will exert on the peer's watchtower service, so the pairing of nodes within a watch swap service is more fair and sustainable. Small nodes will be paired up with small nodes, and larger ones with larger ones. There are five watch swap sizes: Extra Small, Small, Medium, Large and Extra Large.

Applicants can look through the created watch swaps that match their node's size. Non-matching watch swaps will be filtered out from the view. The applicant can apply to the watch swap, but the application is not automatically accepted. The author can accept or reject the application. The reason for this extra approval step is necessary because watching each other node requires some level of trust. Both the applicant and the author will have a chance to assess each other's through their node profile information. If the application gets rejected, the applicant should not get offended, just apply elsewhere or create a watch swap themselves. Once an application is accepted, both parties will be able to see the URI for their peer's watchtower services, so they can add the service to their nodes.

Your watchtower service URI is kept secret from every party until the application is accepted. Once accepted the URI will be shared with your watch swap partner, and nobody else. In general, remember not to share your own or your watch swap partner's watchtower service URI with anyone else, or they may be able to connect to the service uninvited.

All this may feel complex just by reading about it in theory, but LN+ will guide you through the process step by step so it's easy for you in practice.

Before you create a watch swap, please do learn about the following subjects:

Once you're knowledgeable about watchtowers and have the service URI ready, go ahead and start a watch swap or apply to an existing one.

Please do test out watch swaps and let me know if you see any issues, so I can fix them ASAP. Any ideas, recommendations are welcome!