Best Paper Award

  Functional encryption, a key technology for enhancing the security and privacy of cloud computing and big data searches, has been extensively studied in the last decade. It is a generalized and advanced notion of public-key encryption and it offers the functionality of data search by complex formula evaluation in encrypted form and computation on encrypted data with only outputting result values.
   Hiding attributes from ciphertexts (including evaluated data and logical search formulas) is desirable in using functional encryption for various applications, and functional encryption with such an attribute-hiding property is called ‘predicate encryption.’ To clarify which class of functions (or predicates) can be practically realized in predicate encryption is a major challenge in cryptography and this paper addresses the problem. The authors presented a predicate encryption scheme with the most general predicates among those offered by the existing practical schemes. The class is inner product predicates, which is fairly general and includes any constant depth formulas and any constant degree multivariate polynomial functions. In particular, the proposed schemes in this paper are currently the only realization of inner product predicate encryption with the strongest security (under no restriction). That is, this paper answers the question of how general function class can be achieved in the strongest secure predicate encryption.
   To achieve this result, the authors developed a novel security proof methodology. While the existing powerful methodology, dual system encryption, is not effective in proving the strongest security for predicate encryption, only this newly developed methodology offers the strongest security proof for the first time.
   To summarize, this paper marks a culmination in predicate encryption and gives clear evaluations of all of the major results in this area. Hence, the results and methodology obtained and described in this paper are expected to advance and promote this research area and to be applied to various directions. Due to the major contributions described above, this paper is deserving of the IEICE Best Paper Award.