Privacy Preserving Search of Multimedia

The advancement of information technology is rapidly integrating the physical world where we live and the online world where we retrieve and share information. One immediate example of such integration is the increasing popularity of storing and managing personal data using third-party web services, as part of the emerging trend of cloud computing. Secure management of sensitive data stored online is becoming one of the critical research issues in cloud computing and online privacy protection. In this paper, we propose techniques to achieve content based multimedia retrieval over encrypted databases, which can be used for online management of multimedia data while preserving data privacy. We propose two types of secure retrieval schemes by combining cryptographic techniques, such as order preserving encryption and randomized hash functions, with image processing and information retrieval techniques, such as visual words representation, inverted index, and min-hash. The first type of retrieval schemes scramble visual features extracted from images and allow similarity comparison of the features in their encrypted forms. The second type of schemes encrypt the state-of-the-art search indexes without significantly affecting their search capability. The two types of schemes are complementary and represent different tradeoffs between user-side computational complexity and communication overhead. Retrieval results on an encrypted color image database and security analysis under different attack models show that retrieval performance comparable to conventional plaintext retrieval schemes can be achieved over encrypted databases while ensuring data confidentiality.