An Improved Proxy Re-Encryption Scheme for IoT-Based Data Outsourcing Services in Clouds.

IoT-based data outsourcing services in clouds could be regarded as a new trend in recent years, as they could reduce the hardware and software cost for enterprises and obtain higher flexibility. To securely transfer an encrypted message in the cloud, a so-called proxy re-encryption scheme is a better alternative. In such schemes, a ciphertext designated for a data aggregation is able to be re-encrypted as one designated for another by a semi-trusted proxy without decryption. In this paper, we introduce a secure proxy re-encryption protocol for IoT-based data outsourcing services in clouds. The proposed scheme is provably secure assuming the hardness of the bilinear inverse Diffie-Hellman problem (BIDHP). In particular, our scheme is bidirectional and supports the functionality of multi-hop, which allows an uploaded ciphertext to be transformed into a different one multiple times. The ciphertext length of our method is independent of the number of involved IoT nodes. Specifically, the re-encryption process only takes one exponentiation computation which is around 54 ms when sharing the data with 100 IoT devices. For each IoT node, the decryption process only requires two exponentiation computations. When compared with a related protocol presented by Kim and Lee, the proposed one also exhibits lower computational costs.