BIT Problem: Is There a Tradeoff in the Performances of Blockchain Systems? Blockchain technology, as a revolutionary concept, born with Bitcoin, is triggering the start of a new era on information. It is generally recognized that the blockchainbased systems achieve high security in the process of information sharing in a distributed network, at the cost of low efficiency in terms of data throughput or high costs in consuming computational resources. A natural question we are interested in is whether there exists a tradeoff principle between different performances of a blockchain system, which is also regarded as blockchain impossibility triangle (BIT) problem. In this paper, we propose an analysis method which can be used to verify the existence of the BIT. Our analysis method is composed of two layers. In the first layer the basic and core attributes are abstracted by building a consensus model, and in the second layer the analysis approach is designed to verify the existence of a BIT. Specifically, in the first layer, we firstly define a leaderless consensus model to quantitatively abstract the basic parameters in the process of system consensus, then three core attributes are justified to serve as the three vertices of the discussed triangle problem, namely security, cost, and efficiency. Based on the core attributes, we propose the credibility metric which measures the difficulty of achieving credible consensus for a given blockchain system. In the second layer, we analyze the existence of BIT, where we have demonstrated the conditions that a BIT exists and the conditions that the triangle does not exist. Finally, the proposed analysis method is applied in analyzing PoW based blockchain systems, where we have shown that there is no BIT problem in PoW based systems. Furthermore, the proposed analysis method can also help the blockchain developers in finding the promising directions of a new blockchain consensus mechanism.

Weighted Voting on the Blockchain: Improving Consensus in Proof of Stake Protocols Proof of Stake (PoS) protocols rely on voting mechanisms to reach consensus on the current state. If an enhanced majority of staking nodes, also called validators, agree on a proposed block, then this block is appended to the blockchain. Yet, these protocols remain vulnerable to faults caused by validators who abstain either accidentally or maliciously.To protect against such faults while retaining the PoS selection and reward allocation schemes, we study weighted voting in validator committees. We formalize the block creation process and introduce validatorsxe2x80x99 voting profiles which we update by a multiplicative weights algorithm relative to validatorsxe2x80x99 voting behavior and aggregate blockchain rewards. Using this framework, we leverage weighted majority voting rules that optimize collective decision making to show, both numerically and analytically, that the consensus mechanism is more robust if validatorsxe2x80x99 votes are appropriately scaled. We raise potential issues and limitations of weighted voting in trustless, decentralized networks and relate our results to the design of current PoS protocols.