Dependability Analysis for the Blockchain Oracle System: A Quantitative Modeling Approach

Blockchain oracles, as data intermediaries between on-chain and off-chain environments, have opened up a wide range of application scenarios for blockchain technology. The dependability of a blockchain oracle system will affect the dependability of blockchain systems. However, the dynamic and heterogeneous nature of blockchain oracle systems poses challenges to assessing their dependability. Furthermore, how to comprehensively analyze the dependability of blockchain oracle systems from multiple dimensions of transient availability, steady-state availability, and reliability is also a challenge. In order to solve these challenges, this paper proposes three models based on a semi-Markov process (SMP): (1) the SMP model for steady-state availability analysis; (2) the hierarchical model for transient analysis; and (3) the SMP model with absorption states for reliability analysis. Then, we derive the formulas for calculating the dependability metrics, which can be used to evaluate the dependability of blockchain oracle systems composed of any number of oracle nodes. Finally, based on the comparative experiments to verify the approximate accuracy of the proposed model and formulas, we analyze the impact of system parameters and the number of oracle nodes on the dependability metrics. The experimental results reveal that the key factor affecting availability is the failure time and recovery time of the threshold oracle, while the key factor affecting MTTF is the failure time of the threshold oracle.