Secure and Flexible Data Sharing for Distributed Storage with Efficient Key Management

In this paper, we propose a Secure and Flexible Data Sharing (SFDS) scheme for distributed storage, where data owners can outsource their data to a distributed storage network and share the data with authorized users. To preserve confidentiality, all data are encrypted by data owners' secret keys before being outsourced, and fine-grained access policies are enforced on the encrypted data (ciphertexts) to achieve flexible data sharing. Furthermore, based on the ciphertext puncturable encryption and the hierarchical identity-based encryption, we design an efficient key and ciphertext update mechanism, which enables data owners to update their secret keys and the corresponding ciphertexts periodically to deal with side-channel attacks and system vulnerabilities. Update tokens are constructed to directly derive new keys and ciphertexts. Through detailed security analysis, it is demonstrated that SFDS can achieve all three essential security properties, i.e., forward security, post-compromise security, and collusion attack resistance.