Dynamic Policy Attribute Based Encryption and its Application in Generic Construction of Multi-Keyword Search

Attribute based encryption (ABE) is an encryption technique which provides a good solution to the security issues in the cloud environment. Through ABE, a data owner can achieve the fine-grained sharing of data encrypted under attributes or an access policy which they possess. The relation among these attributes is represented by the access policy which is expressed as an access tree. In this article, the authors first present an ABE scheme which supports frequent changes in the access tree and hence, it is named a dynamic policy ABE. Also, the proposed scheme generates secret keys of constant size which can save bandwidth. The proposed scheme is based on key-policy design and supports monotonic access structure that consists of AND, OR and Threshold gates. Inspired by the proposed dynamic policy ABE scheme the authors then present a multi-keyword search scheme which inherits all the features of the proposed ABE scheme. Therefore, it provides a constant size trapdoor and support for fast search. The construction of a multi-keyword search scheme is generic in nature and any ABE scheme can be converted to the multi-keyword search scheme using the transformation method given in the paper. Finally, the proposed schemes are proven to be secure under Decisional Bilinear Diffie-Hellman (DBDH) assumption.