Auditable Register Emulations
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The widespread prevalence of data breaches amplifies the importance of auditing storage systems. Here we initiate the study of auditable storage emulations, which provides the capability for an auditor to discover the previously executed reads in a register. We precisely define the notion of auditable register and its properties, and establish tight bounds and impossibility results for auditable storage emulations in a Byzantine setting. Our formulation considers read-write registers that securely store data using information dispersal and support fast reads. In such scenario, given a maximum number f of faulty storage objects and a minimum number τ of data blocks required to recover a written value, we prove that (1) auditability is impossible if τ≤ 2f; (2) τ≥ 3f+1 is required for implementing a weak form of auditability; and (3) a stronger form of auditability is impossible. We also show that totally ordering operations or using non-fast reads enables such strong auditability, albeit requiring more replicas.
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