This paper presents a novel key-based access control technique for secure outsourcing key-value stores where values correspond to documents that are indexed and accessed using keys. The proposed approach adopts Shamir's secret-sharing that offers unconditional or information-theoretic security. It supports keyword-based document retrieval while preventing leakage of the data, access rights of users, or the size ( i.e. , volume of the output that satisfies a query). The proposed approach allows servers to detect (and abort) malicious clients from gaining unauthorized access to data, and prevents malicious servers from altering data undetected while ensuring efficient access - it takes 231.5ms over 5,000 keywords across 500,000 files.

Information-theoretic or unconditional security provides the highest level of security --- independent of the computational capability of an adversary. Secret-sharing techniques achieve information-theoretic security by splitting a secret into multiple parts (called shares ) and storing the shares across non-colluding servers. However, secret-sharing-based solutions suffer from high overheads due to multiple communication rounds among servers and/or information leakage due to access-patterns ( i.e. , the identity of rows satisfying a query) and volume ( i.e. , the number of rows satisfying a query). We propose S 2 , an information-theoretically secure approach that uses both additive and multiplicative secret-sharing, to efficiently support a large class of selection queries involving conjunctive, disjunctive, and range conditions. Two major contributions of S 2 are: ( i ) a new search algorithm using additive shares based on fingerprints, which were developed for string-matching over cleartext; and ( ii ) two row retrieval algorithms: one is based on multiplicative shares and another is based on additive shares. S 2 does not require communication among servers storing shares and does not reveal any information to an adversary based on access-patterns and volume.