Re-use of patients' health records can provide tremendous benefits for clinical research. Yet, when researchers need to access sensitive/identifying data, such as genomic data, in order to compile cohorts of well-characterized patients for specific studies, privacy and security concerns represent major obstacles that make such a procedure extremely difficult if not impossible. In this paper, we address the challenge of designing and deploying in a real operational setting an efficient privacy-preserving explorer for genetic cohorts. Our solution is built on top of the i2b2 (Informatics for Integrating Biology and the Bedside) framework and leverages cutting-edge privacy-enhancing technologies such as homomorphic encryption and differential privacy. Solutions involving homomorphic encryption are often believed to be costly and immature for use in operational environments. Here, we show that, for specific applications, homomorphic encryption is actually a very efficient enabler. Indeed, our solution outperforms prior work by enabling a researcher to securely compute simple statistics on more than 3,000 encrypted genetic variants simultaneously for a cohort of 5,000 individuals in less than 5 seconds with commodity hardware. To the best of our knowledge, our privacy-preserving solution is the first to also be successfully deployed and tested in a operation setting (Lausanne University Hospital).

Timed-release encryption allows senders to send a message to a receiver which cannot decrypt until a server releases a time bound key at the release time. The release time usually supposed to be known to the receiver, the ciphertext therefore cannot be decrypted if the release time is lost. We solve this problem in this paper by having a master time bound key which can replace the time bound key of any release time. We first present security models of the timed-release encryption with master time bound key. We present a provably secure construction based on the Weil pairing.

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Current proposals of extractable witness encryption are based on multilinear maps. In this paper, we propose a new construction without.We propose the notion of hidden group with hashing and make an extractable witness encryption from it. We show that the construction is secure in a generic model. We propose a concrete construction based on RSA-related problems. Namely, we use an extension of the knowledgeof-exponent assumption and the order problem. Our construction allows to encrypt for an instance of the subset sum problem (actually, a multidimensional variant of it) for which short solutions to the homogeneous equation are hard to find. Alas, we do not propose any reduction from a known NP-complete problem.

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