Message-locked encryption with file update

Abstract

Message-locked encryption (MLE) (formalized by Bellare et al. [5]) is an important cryptographic primitive that supports deduplication in the cloud. Updatable block-level message-locked encryption (UMLE) (formalized by Zhao and Chow [13]) adds the update functionality to the MLE. In this paper, we formalize and extensively study a new cryptographic primitive file-updatable message-locked encryption (FMLE). FMLE can be viewed as a generalization of the UMLE, in the sense that unlike the latter, the former does not require the existence of BL-MLE (block-level message-locked encryption). FMLE allows more flexibility and efficient methods for updating the ciphertext and tag. Our second contribution is the design of two efficient FMLE constructions, namely, RevD-1 and RevD-2, whose design principles are inspired from the very unique reverse decryption functionality of the FP hash function (designed by Paul et al. [11]) and the APE authenticated encryption (designed by Andreeva et al. [2]). With respect to UMLE – which provides so far the most efficient update function – RevD-1 and RevD-2 reduce the total update time by at least 50%, on average. Additionally, our constructions are storage efficient. We also give extensive comparison between our and the existing constructions.