Secure index search for groups

A secure index search protocol makes it possible to search for the index of encrypted documents using specified keywords even without decrypting them. An untrusted server storing the documents learns nothing more than the search result about the documents without revealing the keyword. Secure index search protocols in the literature only consider a search process between a single-user and a server. However, in real organizations such as government offices or enterprises with many departments, a group search occurs more often. In this paper, we study natural extension of previous results, i.e., secure index search between a server and group members, where a file may be shared by a group or a person with a server. The difficulty in designing such a group setting arises from dynamic group, where each member of the group may join to or leave from the group. To resolve this difficulty efficiently, we propose novel secure index search protocols without reencryption of the old encrypted documents when group keys are updated.