Secure server-aided data sharing clique with attestation

Abstract In this paper, we consider the security issues in data sharing cliques via remote server. We present a public key re-encryption scheme with delegated equality test on ciphertexts (PRE-DET). The scheme allows users to share outsourced data on the server without performing decryption-then-encryption procedures, allows new users to dynamically join the clique, allows clique users to attest the message underlying a ciphertext, and enables the server to partition outsourced user data without any further help of users after being delegated. We introduce the PRE-DET framework, propose a concrete construction and formally prove its security against five types of adversaries regarding two security requirements on message confidentiality and unforgeability of attestation against the server. We also theoretically analyze and compare the proposed PRE-DET construction with related schemes in terms of ciphertext sizes and computation costs of encryption, decryption, ciphertext equality testing and re-encryption, which confirms the practicality of our construction.