Design Issues in Permissioned Blockchains for Trusted Computing

A permissioned blockchain (BC) is a secure distributed ledger maintained by a number of trusted validation nodes. However, a validator may become compromised and send inconsistent messages to different nodes. To counter the problem, consensus protocols like Practical Byzantine Fault Tolerance (PBFT) can be used. The paper presents a permissioned BC system and discusses various design issues including control messages, block size and window size of block creation time. Furthermore, it is necessary to identify those compromised nodes discovered during the consensus protocol. This paper then proposes a reputation system to track the trustworthiness of nodes as it is necessary to distinguish failed nodes from compromised nodes. A compromised node may send inconsistent messages to others or accuse other nodes compromised, and it should be removed as soon as it is identified and confirmed.