In the use of a cloud storage, sharing of data with efficient access control is an important requirement in addition to data security and privacy. Cui et al. (IEEE Trans. on Comp. 2016) proposed key-aggregate searchable encryption (KASE), which allows a data owner to issue an aggregate key that enables a user to search in an authorized subset of encrypted files by generating an encrypted keyword called trapdoor. While the idea of KASE is elegant, to the best of our knowledge, its security has never been discussed formally. In this paper, we discuss the security of KASE formally and propose provably secure schemes. The construction of a secure KASE scheme is non-trivial, and we will show that the KASE scheme of Cui et al. is insecure under our definitions. We first introduce our provably secure scheme, named first construction, with respect to encrypted files and aggregate keys in a single-server setting. In comparison with the scheme of Cui et al., the first construction is secure without increased computational costs. Then, we introduce another provably secure scheme, named main construction, with respect to trapdoors in a twoserver setting. The main construction guarantees the privacy of a search, encrypted files, and aggregate keys. Considering 5,000 encrypted files, the first construction can finish search within three seconds and the main construction can finish search within six seconds.INDEX TERMS Key-Aggregate Searchable Encryption, Searchable Encryption, Data Sharing and Provable Security.
Stimulus-responsive biomolecules are attractive targets to understand biomolecule behaviour as well as to explore their therapeutic and diagnostic applications. We demonstrate that a reduction-responsive cleavable group (chemically caged unit) introduced into the guanine ring enables modulation of the secondary structure transition of an oligonucleotide in a reduction-responsive and traceless manner leaving the unmodified oligonucleotide of interest. This simple but robust strategy could yield a variety of stimuli-responsive oligonucleotides.
The cover picture shows the reduction‐responsive structural transition of an oligonucleotide bearing a newly designed chemically reactive nucleobase (GNB) from random‐coil to G‐quadruplex structure. Stimuli‐responsive oligonucleotides are attractive targets for understanding the behaviour of biomolecules as well as for exploring their therapeutic and diagnostic applications. We have demonstrated that a reduction‐responsive cleavable group, 4‐nitrobenzyl (NB), introduced into a guanine nucleobase modulates the secondary structural transition of an oligonucleotide in a reduction‐responsive and traceless manner. This simple but robust strategy will provide important chemical tools for developing stimuli‐responsive oligonucleotides. More information can be found in the communication by M. Ikeda, Y. Kitade, et al. on page 1304 in Issue 14, 2016 (DOI: 10.1002/cbic.201600164).
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