Paper 2018/918

Scalable Lightning Factories for Bitcoin

Alejandro Ranchal-Pedrosa, Maria Potop-Butucaru, and Sara Tucci-Piergiovanni

Abstract

Bitcoin, the most popular blockchain system, does not scale even under very optimistic assumptions. Lightning networks, a layer on top of Bitcoin, composed of one-to-one lightning channels make it scale to up to 105 Million users. Recently, Duplex Micropayment Channel factories have been proposed based on opening multiple one-to-one payment channels at once. Duplex Micropayment Channel factories rely on time-locks to update and close their channels. This mechanism yields to situation where users funds time-locking for long periods increases with the lifetime of the factory and the number of users. This makes DMC factories not applicable in real-life scenarios. In this paper, we propose the first channel factory construction, the Lightning Factory that offers a constant collateral cost, independent of the lifetime of the channel and members of the factory. We compare our proposed design with Duplex Micropayment Channel factories, obtaining better performance results by a factor of more than 3000 times in terms of the worst-case constant collateral cost incurred when malicious users use the factory. The message complexity of our factory is $n$ where Duplex Micropayment Channel factories need $n^2$ messages where $n$ is the number of users. Moreover, our factory copes with an infinite number of updates while in Duplex Micropayment Channel factories the number of updates is bounded by the initial time-lock. Finally, we discuss the necessity for our Lightning Factories of BNN, a non-interactive aggregate signature cryptographic scheme, and compare it with Schnorr and ECDSA schemes used in Bitcoin and Duplex Micropayment Channels.