SUPRA, a distributed publish/subscribe protocol with blockchain as a conflict resolver

Publish/subscribe is a communication paradigm used in distributed applications to easily exchange messages. This paradigm usually has a centralized architecture where a broker is responsible for transferring all the messages, hence can be a source of trust issues. In a threat model where the broker can be malicious, two honest entities cannot be sure of the origin of a message. There exist propositions for distributed publish/subscribe protocols replacing the broker by a blockchain. Those propositions all have in common an extensive usage of the blockchain, which makes them expensive over time, due to blockchain fees, and not scalable. In this paper, we introduce SUPRA, a distributed publish/subscribe protocol. This protocol has the same security guarantees than other solutions relying on blockchains, but where the vast majority of messages are off-chain. The message exchanges are done mostly directly between publishers and subscribers and the blockchain is only used in case of network issues, if a message is lost, or an entity is suspected to be malicious.