Verifiable Message-Locked Encryption

One of today’s main challenge related to cloud storage is to maintain the  functionalities and the efficiency of customers’ and service providers’ usual  environments while protecting the confidentiality of sensitive data. Deduplication is one of those functionalities: it enables cloud storage providers to save a lot of  memory by storing only once a file uploaded several times. However, classical  encryption schemes block deduplication. One needs to use a “message-locked  encryption” scheme (MLE), which allows the detection of duplicates and the  storage of only one encrypted file on the server, which can be decrypted by any  owner of the file. However, in most existing scheme, a user can bypass this  deduplication protocol. In this article, we provide servers verifiability for MLE schemes: the servers can verify that the ciphertexts are well-formed. This property  forces a customer to prove that she complied to the deduplication  protocol, thus preventing her to deviate from the prescribed functionality of MLE. Then, we provide an MLE scheme satisfying this new security property. To  achieve the deduplication consistency, our construction primarily relies on  zero-knowledge proofs. Unlike Abadi et al.’s MLE, we instantiate those proofs, so
that we obtain a more efficient scheme, secure in the random oracle model.