IACR News item: 11 October 2014
Divesh Aggarwal, Yevgeniy Dodis, Tomasz Kazana, Maciej Obremski
ePrint ReportThe family which received the most attention~\\cite{DPW10,LL12,DKO13,ADL14,CG14a,CG14b} is the family of tampering functions in the so called {\\em split-state} model: here the message $x$ is encoded into two shares $L$ and $R$,
and the attacker is allowed to {\\em arbitrarily} tamper with each $L$ and $R$ {\\em individually}.
Despite this attention, the following problem remained open:
\\begin{center}
{\\em Build efficient, information-theoretically secure non-malleable codes in the split-state model with constant encoding rate}: $|L|=|R|=O(|x|)$.
\\end{center}
In this work, we resolve this open problem. Our technique for getting our main result is of independent interest. We
\\begin{itemize}
\\item[(a)] develop a generalization of non-malleable codes, called {\\em non-malleable reductions};
\\item[(b)] show simple composition theorem for non-malleable reductions;
\\item[(c)] build a variety of such reductions connecting various (independently interesting) tampering families $\\cF$ to each other; and
\\item[(d)] construct our final, constant-rate, non-malleable code in the split-state model by applying the composition theorem to a series of easy to understand reductions.
\\end{itemize}
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