Non-malleable Codes from Two-Source Extractors

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We construct an efficient information-theoretically non-malleable code in the split-state model for one-bit messages. Non-malleable codes were introduced recently by Dziembowski, Pietrzak and Wichs (ICS 2010), as a general tool for storing messages securely on hardware that can be subject to tampering attacks. Informally, a code \((\mathsf{Enc} : {\cal M} \rightarrow {\cal L} \times {\cal R}, \mathsf{Dec} : {\cal L} \times {\cal R} \rightarrow {\cal M})\) is non-malleable in the split-state model if any adversary, by manipulating independently L and R (where (L,R) is an encoding of some message M), cannot obtain an encoding of a message M′ that is not equal to M but is “related” M in some way. Until now it was unknown how to construct an information-theoretically secure code with such a property, even for \({\cal M} = \{0,1\}\) . Our construction solves this problem. Additionally, it is leakage-resilient, and the amount of leakage that we can tolerate can be an arbitrary fraction ξ < 1/4 of the length of the codeword. Our code is based on the inner-product two-source extractor, but in general it can be instantiated by any two-source extractor that has large output and has the property of being flexible, which is a new notion that we define.

We also show that the non-malleable codes for one-bit messages have an equivalent, perhaps simpler characterization, namely such codes can be defined as follows: if M is chosen uniformly from {0,1} then the probability (in the experiment described above) that the output message M′ is not equal to M can be at most 1/2 + ε.

This work was partly supported by the WELCOME/2010-4/2 grant founded within the framework of the EU Innovative Economy (National Cohesion Strategy) Operational Programme. The European Research Council has provided financial support for this work under the European Community’s Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no CNTM-207908.