Collusion-Resistant Processing of SQL Range Predicates

Abstract

Prior solutions for securely handling SQL range predicates in outsourced cloud-resident databases have primarily focused on passive attacks in the Honest-but-Curious adversarial model, where the server is only permitted to observe the encrypted query processing. We consider here a significantly more powerful adversary, wherein the server can launch an active attack by clandestinely issuing specific range queries via collusion with a few compromised clients. The security requirement in this environment is that data values from a plaintext domain of size N should not be leaked to within an interval of size \(H\). Unfortunately, all prior encryption schemes for range predicate evaluation are easily breached with only \(O(log_2\psi )\) range queries, where \(\psi = N/H\). To address this lacuna, we present SPLIT, a new encryption scheme where the adversary requires exponentially more – \(\mathbf{O}(\psi )\) – range queries to breach the interval constraint, and can therefore be easily detected by standard auditing mechanisms.