Altruistic Watchtowers for LND

Posted over 3 years ago by Lightning Hoarder

Watchtowers are an utility for Lightning Network nodes to protect them against outdated channel states being published by counterparties. They do so without having to trust them with any key material, just the responsibility of checking chain state and publishing them when necessary.

This is something you should be using on your node. In this post we will discuss specifically Private Altruist Watchtowers for LND. We also have a list of several up-to-date watchtowers ready to use.

From Watchtowers | Bitcoin Optech:

Watchtowers send LN breach remedy transactions (justice transactions) when they detect that one of their client’s counterparty has broadcast an outdated channel close transaction.

The service provided by watchtowers allows their clients to go offline for significant amounts of time without having to worry about their funds being stolen by a counterparty. Watchtowers are not entrusted with any funds, just the responsibility of monitoring the block chain and broadcasting transactions, although breach remedy transactions can be designed so that the watchtower receives a portion of the safeguarded funds if their services are needed.

On LND you can connect to remote watchtowers, but also run your own. Check the LND Documentation | Private Altruist Watchtowers for more general information about them.

Watchtowers do not store transactions directly, but they are given encrypted by your node. The only way they can decrypt them is after an obsolete commitment is published on-chain. At that time they will publish the punishment (they cannot alter this transaction), and you have been protected against a malicious/failing counterparty without your node having to be online. It is recommended to use multiple watchtowers to not depend on single ones. If you want more technical details, check the BOLT13 draft

Most watchtowers run on Tor addresses, although there are a few running on clear net IPs. As such, having Tor at least outbound is recommended to use watchtowers.

To add a new watchtower to LND, you can run a command like this (with an example tower):

$ lncli wtclient add 025d21fc580d854052e7087670ac85283dd10db7b273fc697827520a34360279db@looplnk2vszfniwkiqi66pq5tpkuslzobpo3x6jkpgjzm4jbq7i6f5qd.onion:9911

If you are looking for watchtowers to use, there are several resources:

openoms/lightning-node-management#4 "Watchtower list" on Github, where various people post their own watchtowers. Some work, some don't. Feel free to post yours.
Known LND Watchtowers on ln.LightningHoarder.net, listing various Tor and Clear Net addresses that have been tested to be working. These addresses have been collected from GitHub, Reddit, 1ML, and other sources. It is updated regularly.
Watch Tower Directory on 1ML.com. Several nodes have self-tagged with Watch Tower tag, though most don't run one. See their descriptions for any watchtowers, very hit/miss.

If you want to add many in bulk, you can use this command, that uses the lists provided on ln.LightningHoarder.net:

curl https://ln.lightninghoarder.net/known-lnd-watchtowers.txt | xargs -L1 lncli wtclient add

Hope you enjoy, and have a safe Lightning journey!

- Lightning Hoarder

If you want to send any tips, feel free to KeySend my node or use patron.lightninghoarder.net.

4 Comments

LN+ Admin wrote over 3 years ago

This is very cool. Would you recommend we build some sort of feature here on LN+ to make this easier for node operators to be protected by altruistic watchtowers?

Lightning Hoarder wrote over 3 years ago

@LN+: Yes! That would be great. A listing of watchtowers (or ability to specify a watchtower address on your profile, they are different from node pubkey/address), and automatic testing of them (connect + maybe general pubkey check).

poolside-roma wrote over 3 years ago

Added some, thank you for this post!

Cuaritas wrote over 3 years ago

I keysend you some sats, Thank you for this post!!! <3

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