Red Belly Blockchain

We present the Balance Attack that can lead an adversary to double spend coins in proof-of-work blockchains. The Balance Attack bridges the gap between attacks that require to partition the network and attacks that require high mining power as it shows that one needs less mining power if it can delay network messages longer. We show that the attack succeeds with high probability even when the adversary has a less than half of the mining power. We also analyze theoretically the probability of success of the attack depending on the (i) difficulty of the crypto-puzzle that the proof-of-work solves, (ii) the network delay that the attacker introduces and (iii) the mining power of the attacker. 

As an alternative to the energy greedy proof-of-work, new blockchains constrain the set of participants whose selection is debatable. These blockchains typically allow a fixed consortium of machines to decide upon new transaction blocks. In this paper, we introduce the community blockchain that bridges the gap between these public blockchains and constrained blockchains. The idea is to allow potentially all participants to decide upon “some” block while restricting the set of participants deciding upon “one” block. We also propose an implementation called ComChain that builds upon the Red Belly Blockchain, the fastest blockchain we are aware of. It runs a consensus among the existing community to elect a new community. This reconfiguration speeds up as the number of removed nodes increases.

Blockchain is an emerging technology for decentralized and transactional data sharing across a large network of untrusted participants. It enables new forms of distributed software architectures, where components can find agreements on their shared states without trusting a central integration point or any particular participating components. Considering the blockchain as a software connector helps make explicitly important architectural considerations on the resulting performance and quality attributes (for example, security, privacy, scalability and sustainability) of the system. Based on our experience in several projects using blockchain, in this paper we provide rationales to support the architectural decision on whether to employ a decentralized blockchain as opposed to other software solutions, like traditional shared data storage. Additionally, we explore specific implications of using the blockchain as a software connector including design trade-offs regarding quality attributes..