Somewhat semantic secure public key encryption with filtered-equality-test in the standard model and its extension to searchable encryption

Public key encryption with equality test (PKE-ET) is a public key encryption with an extra functionality, so-called 'equality test'. An authorized third party can verify the equivalence between two ciphertexts encrypted under different public keys, while the decryption keeps unavailable. However, the privacy of most existing PKE-ET schemes drop to one-way security owing to the 'equality test' functionality. In this work, we propose a novel architecture called filtered equality test (FET), which 'filtered' denotes only few receiver-selected messages can be equality tested. In such model, we propose an equality test scheme, PKE-FET, which is the first one to be proved (somewhat) semantic secure. The concrete PKE-FET scheme and its rigorous security proof in the standard model are proposed. Furthermore, FET is also applied to construct a searchable encryption named PE-MKS, which is inherently proved semantic secure (so called the indistinguishability against chosen keyword attacks) in the standard model.