Secure Queries on Encrypted Multi-writer Tables

Performing searches on encrypted data is a very current and active area. Several efficient solutions have been provided for the single-writer scenario in which all sensitive data originates with one party (the Data Owner) that encrypts it and uploads it to a public repository. Subsequently, the Data Owner (or authorized clients, the Query Sources) perform queries on the encrypted data through a Query Processor which has direct access to the public repository. Motivated by the recent trend in pervasive data, we depart from this model and consider a multi-writer scenario in which data originates with several and mutually untrusted parties. In this new scenario the Data Owner provides public parameters so that each piece of the generated data stream can be put into an encrypted stream; moreover, the Data Owner keeps some related secret information needed to generate tokens so that different subscribers can access different subsets of the encrypted stream in clear. We consider the case in which each piece of the data stream consists of a fixed number of cells, organized in columns, and the data owner can authorize subscribers to access individual data based on the content of the columns. Current public-key functional encryption schemes provide a direct and impractical implementation of this scenario. We thus propose a new public-key primitive, Amortized Orthogonality Encryption or AOE, derived from Inner-Product Encryption, that can be used to encrypt each piece of data stream so that ciphertexts have size proportional to the un-encrypted data; moreover, encryption and decryption take time proportional to the number of columns. Previous schemes would give quadratic complexity. We provide a construction of AOE and prove its selective security under standard assumptions in a bilinear setting with prime order group. Using AOE, we implement all the basic operations in our multi-writer scenario in one round of communication. We demonstrate the feasibility and effectiveness of our proposal by providing an implementation of our scenario in C++.