The Bitcoin Lightning Network (LN) developer community is working to improve the security and accountability of watchtowers, the nodes that protect user payment channels on the network.

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Sergi Delgado Segura, a Bitcoin developer, posted on the Lightning-Dev mailing list last week a proposal to hold watchtowers accountable for failing to respond to protocol violations they might have detected.

The basic principle is that each watchtower has a known public key and uses the corresponding private key to generate a signature for any violation detection data it accepts.

 If a watchtower does not respond to a violation, the user could post the data and signature to prove that the watchtower did not meet its responsibility.

However, Delgado pointed out that there are practical problems with this approach, such as the fact that the user would have to store an additional signature each time they send new data to the watchtower for violation detection, which could sometimes be quite frequent in active LN channels.

Additionally, some Watchtowers may want to store data only temporarily, which poses a problem if breach detection data is required to be stored permanently.

Delgado suggests using crypto accumulators. These provide a practical solution on data storage and verification of violations by Watchtowers.

The watchtower nodes have been a fundamental piece in the growth of the Bitcoin Lightning network. Since its creation in 2019, as reported by CriptoNoticias, they “monitor” the network, avoiding unilateral channel closures or improper payments.

The creation of this type of tools facilitated the use of the Lightning network, since now it does not require that a user must be connected to their wallet or node to receive a payment. The Watchtower is in charge of ensuring that everything happens normally.

What are crypto accumulators

A cryptographic accumulator is a data structure that allows a user to add items to a list and generate a cryptographic proof without revealing the individual items in the list. 

In other words, it allows multiple inputs to be combined into a single cryptographic proof, making it useful in many applications such as voting systems, social networks, and authentication systems.

The use of cryptographic accumulators has been proposed as a way to improve privacy and scalability in a variety of applications, including blockchains. 

For example, instead of storing all transactions on a blockchain, they could be stored in a cryptographic accumulator and only the cryptographic proof of the aggregation would be added to the blockchain. This could improve the scalability and privacy of the blockchain.

Thanks to this advantage provided by cryptographic accumulators, validations and data storage would be easier to share, avoiding overloads on Watchtowers. 

It should be noted that at the moment it is only a proposal that is still under discussion and has not been implemented within the source code of the Lightning network.