Biblio

As a decentralized ledger technology, blockchain is considered to be a potential solution for applications with highly concentrated management mechanism. However, most of the existing blockchain networks are employed with the hash-puzzle-solving consensus protocol, known as proof-of-work. The competition of solving the puzzle introduces high latency, which directly leads to a long transaction-processing time. One solution of this dilemma is to establish a blockchain network with shards. In this paper, we focus on the blockchain network with shards and adopt the security-deposit based consensus protocol, studying the problem of how to balance the security incentive and the economic incentive. Also, the inherent features of the blockchain, i.e., anonymity and decentralization, introduce the information asymmetric issue between the beacon chain and the participants. The contract theory is utilized to formulate the problem between them. As such, the optimal rewards related to the different types of validators can be obtained, as well as the reasonable deposits accordingly. Compared with the fixed deposits, the flexible deposits can provide enough economic incentive for the participants without losing the security incentives. Besides, the simulation results demonstrate that the contract theory approach is capable of maximizing the beacon chain's utility and satisfying the incentive compatibility and individual rationality of the participants.

Blockchain networks which employ Proof-of-Work in their consensus mechanism may face inconsistencies in the form of forks. These forks are usually resolved through the application of block selection rules (such as the Nakamoto consensus). In this paper, we investigate the cause and length of forks for the Bitcoin network. We develop theoretical formulas which model the Bitcoin consensus and network protocols, based on an Erdös-Rényi random graph construction of the overlay network of peers. Our theoretical model addresses the effect of key parameters on the fork occurrence probability, such as block propagation delay, network bandwidth, and block size. We also leverage this model to estimate the weight of fork branches. Our model is implemented using the network simulator OMNET++ and validated by historical Bitcoin data. We show that under current conditions, Bitcoin will not benefit from increasing the number of connections per node.

Blockchain networks have been claimed to have the potential of fundamentally changing the way humans perform economic transactions with each other. In such networks, trust-enabling agents and activities, that were traditionally arranged in a centralized fashion, are replaced by a network of nodes which collectively yet independently witness and establish the non-repudiability of transactions. Most often, a proof-of-work (PoW) requirement ensures that participants invest resources for joining the network, incentivizing conformance to the network rules, while making it highly infeasible for malicious agents to construct an alternative version of the transaction history. While research on security and efficiency aspects of blockchain networks is already being conducted, there is still work to be done to understand how different external and internal conditions guarantee or threaten their sustainability, i.e., their continuous operation. Focusing on public PoW-based blockchain platforms, in this paper we sketch an abstract model that is aimed at supporting comprehension and qualitative reasoning about the factors that affect sustainability of a blockchain network.