In order to protect privacy of sensitive data, the content
owners tend to convert the multimedia data into
unrecognizable data before outsourcing, which may be
not compliant with plaintext-based traditional information
retrieval techniques. So, the need for privacy-preserving
and effective information retrieval becomes urgent.
The problem of information retrieval in encrypted do-
main has been investigated for many years. In particular,
secure searchable mechanisms for text documents have
become an active research area that considers an appli-
cation scenario where the content owners supply
encrypted text documents and indices, while the servers
provide search service without knowing the plaintext