Secure deduplication with efficient user revocation in cloud storage.

• We propose a multi-user updatable encryption scheme, in which a data owner can update the remote ciphertext to a new group of users. • We adopt the multi-user updatable encryption to construct a secure deduplication scheme supporting lightweight user revocation. • Our proposed deduplication scheme saves communication and computation costs dramatically. Secure deduplication is a promising solution to greatly reduce the storage space of the cloud. However, the encryption key is deterministically derived from the plaintext, such that who owns the plaintext has the derived key to decrypt the ciphertext. Therefore, how to revoke a user in deduplication schemes is a critical challenge. In the existing work, when updating the data authority, the data owner has to download the data from the cloud, decrypt, re-encrypt and finally upload them to the cloud. This process increases the communication and computation overheads. In this paper, we first propose a multi-user updatable encryption scheme. Specifically, the data owner can update the remote ciphertext under a new group key by sending an update token to the cloud. Then we adopt this technique to propose a new secure deduplication scheme supporting efficiently revoking an unauthorized user. In our scheme, the data owner just needs to send a token to the cloud to update the data authority, which saves the communication and computation costs. The security and efficiency analysis demonstrate that our proposed deduplication scheme can achieve the desired security properties with high efficiency. [ABSTRACT FROM AUTHOR]