Tradeoffs in Permissioned vs Permissionless Blockchains : Trust and Performance

It is generally agreed that permissioned blockchains can improve on the operational cost and performance of permissionless blockchains, but it is usually assumed that this improvement comes at the cost of transaction security, especially in low-trust environments. We develop a model of transaction safety in permissioned and permissionless blockchains to study this tradeoff and find that in several settings there may be no tradeoff at all. With a minimal level of trust in the blockchain operators and the supporting institutions, well-designed permissioned blockchains can offer both higher operational efficiency and higher transaction security. While this minimal trust in the ``system'' is essential to the functioning of permissioned blockchains, it is also inherent in most business relationships, making permissioned blockchains well suited for enterprise applications of the technology. We explore the implications of our analysis for the design of permissioned blockchains, such as the reputation or bonding implications for their validators