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Non-Malleable Coding Against Bit-wise and Split-State Tampering

Mahdi Cheraghchi, Venkatesan Guruswami

arXiv, 2013

Abstract

Non-malleable coding, introduced by Dziembowski, Pietrzak and Wichs (ICS 2010), aims for protecting the integrity of information against tampering attacks in situations where error-detection is impossible. Intuitively, information encoded by a non-malleable code either decodes to the original message or, in presence of any tampering, to an unrelated message. Dziembowski et al. show existence of non-malleable codes for any class of tampering functions of bounded size. We consider constructions of coding schemes against two well-studied classes of tampering functions: bit-wise tampering functions (where the adversary tampers each bit of the encoding independently) and split-state adversaries (where two independent adversaries arbitrarily tamper each half of the encoded sequence). 1. For bit-tampering, we obtain explicit and efficiently encodable and decodable codes of length $n$ achieving rate $1-o(1)$ and error (security) $\exp(-\tildeΩ(n^{1/7}))$. We improve the error to $\exp(-\tildeΩ(n))$ at the cost of making the construction Monte Carlo with success probability $1-\exp(-Ω(n))$. Previously, the best known construction of bit-tampering codes was the Monte Carlo construction of Dziembowski et al. (ICS 2010) achieving rate ~.1887. 2. We initiate the study of seedless non-malleable extractors as a variation of non-malleable extractors introduced by Dodis and Wichs (STOC 2009). We show that construction of non-malleable codes for the split-state model reduces to construction…

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