We consider the following problem: members in a dynamic group retrieve their encrypted data from an untrusted server based on keywords and without any loss of data confidentiality and member's privacy. In this paper, we investigate common secure indices for conjunctive keyword-based retrieval over encrypted data, and construct an efficient scheme from Wang et al. dynamic accumulator, Nyberg combinatorial accumulator and Kiayias et al. public-key encryption system. The proposed scheme is trapdoorless and keyword-field free. The security is proved under the random oracle, decisional composite residuosity and extended strong RSA assumptions.Keywords: Common secure index, conjunctive keyword search, dynamic accumulator.Related Works. Song, Wagner, and Perrig [14] first introduced the notion of searchable encryption for a single-user. They proposed a scheme in the symmetric key setting, which encrypts each word (or each pattern) of a document separately.

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