Equivalence-based Security for Querying Encrypted Databases: Theory and Application to Privacy Policy Audits

TL;DR

This paper introduces two encryption schemes for cloud databases that balance data confidentiality with query usability, supported by a new security definition based on database equivalence, and demonstrates practical application in privacy policy audits.

Contribution

It proposes novel encryption schemes with a formal security framework and applies them to privacy policy violation detection with low overhead.

Findings

Schemes effectively hide data while supporting relational queries.

Security defined via database equivalence from adversary's perspective.

Application to privacy policy audits shows low to moderate overheads.

Abstract

Motivated by the problem of simultaneously preserving confidentiality and usability of data outsourced to third-party clouds, we present two different database encryption schemes that largely hide data but reveal enough information to support a wide-range of relational queries. We provide a security definition for database encryption that captures confidentiality based on a notion of equivalence of databases from the adversary's perspective. As a specific application, we adapt an existing algorithm for finding violations of privacy policies to run on logs encrypted under our schemes and observe low to moderate overheads.