  Blockchain technology enables stakeholders to conduct trusted data sharing
and exchange without a trusted centralized institution. These features make
blockchain applications attractive to enhance trustworthiness in very different
contexts. Due to unique design concepts and outstanding performance, blockchain
has become a popular research topic in industry and academia in recent years.
Every participant is anonymous in a permissionless blockchain represented by
cryptocurrency applications such as Bitcoin. In this situation, some special
incentive mechanisms are applied to permissionless blockchain, such as mined
native cryptocurrency to solve the trust issues of permissionless blockchain.
In many use cases, permissionless blockchain has bottlenecks in transaction
throughput performance, which restricts further application in the real world.
A permissioned blockchain can reach a consensus among a group of entities that
do not establish an entire trust relationship. Unlike permissionless
blockchains, the participants must be identified in permissioned blockchains.
By relying on the traditional crash fault-tolerant consensus protocols,
permissioned blockchains can achieve high transaction throughput and low
latency without sacrificing security. However, how to balance the security and
consensus efficiency is still the issue that needs to be solved urgently in
permissioned blockchains. As the core module of blockchain technology, the
consensus algorithm plays a vital role in the performance of the blockchain
system. Thus, this paper proposes a new consensus algorithm for permissioned
blockchain, the Risk Assessment-based Consensus protocol (RAC), combined with
the decentralized design concept and the risk-node assessment mechanism to
address the unbalance issues of performance in speed, scalability, and
security.
