  In this paper, we present a novel Secured Outsourced Content Based Image
Retrieval solution, which allows looking for similar images stored into the
cloud in a homomorphically encrypted form. Its originality is fourfold. In a
first time, it extracts from a Paillier encrypted image a wavelet based global
image signature. In second, this signature is extracted in an encrypted form
and gives no clues about the image content. In a third time, its calculation
does not require the cloud to communicate with a trusted third party as usually
proposed by other existing schemes. More clearly, all computations required in
order to look for similar images are conducted by the cloud only with no
extra-communications. To make possible such a computation, we propose a new
fast way to compare encrypted data, these ones being encrypted by the same
public key or not, and using a recursive relationship in-between Paillier
random values when computing the different resolution levels of the image
wavelet transform. Experiments conducted in two distinct frameworks: medical
image retrieval with as purpose diagnosis aid support, and face recognition for
user authentication; indicate that the proposed SOCBIR does not change image
retrieval performance.
