Cryptology ePrint Archive: Report 2015/440

Message-Locked Encryption for Lock-Dependent Messages

Martín Abadi and Dan Boneh and Ilya Mironov and Ananth Raghunathan and Gil Segev

Abstract: Motivated by the problem of avoiding duplication in storage systems, Bellare, Keelveedhi, and Ristenpart have recently put forward the notion of Message-Locked Encryption (MLE) schemes which subsumes convergent encryption and its variants. Such schemes do not rely on permanent secret keys, but rather encrypt messages using keys derived from the messages themselves.

We strengthen the notions of security proposed by Bellare et al. by considering plaintext distributions that may depend on the public parameters of the schemes. We refer to such inputs as lock-dependent messages. We construct two schemes that satisfy our new notions of security for message-locked encryption with lock-dependent messages. Our main construction deviates from the approach of Bellare et al. by avoiding the use of ciphertext components derived deterministically from the messages. We design a fully randomized scheme that supports an equality-testing algorithm defined on the ciphertexts.

Our second construction has a deterministic ciphertext component that enables more efficient equality testing. Security for lock-dependent messages still holds under computational assumptions on the message distributions produced by the attacker.

In both of our schemes the overhead in the length of the ciphertext is only additive and independent of the message length.

Category / Keywords: public-key cryptography / deduplication, message-locked encryption, cloud storage

Original Publication (in the same form): IACR-CRYPTO-2013

Date: received 7 May 2015

Contact author: ananthr at cs stanford edu

Available format(s): PDF | BibTeX Citation

Version: 20150508:112157 (All versions of this report)

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