Blockstream's 'Watchtowers' Will Bring a New Justice System to the Lightning Network

Watchtowers, a semi-trusted payment channel sheriff, will keep the peace among lightning nodes.

Spearheaded by Blockstream's c-Lightning team, the Watchtowers are part of Eltoo, a proposed enforcement layer for the lightning network.

Currently, lightning uses fraud proofs to extract justice on the network from channels that steal funds.

With Eltoo, users who are often offline can defer to Watchtowers to protect their funds for them.

Not altogether a novel concept, the feature has been experimented with by lightning groups Electrum and Lightning Labs, though the implementation will be a first for c-Lightning.

Watchtowers were first pushed for on c-Lightning by developers Sergi Delgado Segura and Patrick McCorry in late November.

As a semi-trusted peacekeeper, Watchtowers store local information from subscribing nodes and are purpose-built for nodes that go offline frequently, such as cell phones, which have quickly become a popular way to participate in the lightning network, Decker said.

"Watchtowers are most important when you run stuff on an unreliable network connections, so you maybe cannot check back in with the blockchain to react in time or you have devices that are often offline," Decker said.

Watchtowers are expensive to maintain as they store lots of local data, Decker said.

Who will operate them remains to be seen, particularly as the lightning fee market remains immature.