International Association
for Cryptologic Research

A non-malleable code protects messages against various classes of tampering.

Informally, a code is non-malleable if the effect of applying any tampering

function on an encoded message is to either retain the message or to replace

it with an unrelated message.

Two main challenges in this area -- apart from establishing

the feasibility against different families of tampering -- are to obtain

{\\em explicit constructions} and to obtain {\\em high-rates} for such

constructions.

In this work, we present a compiler to transform low-rate (in fact, zero

rate) non-malleable codes against certain class of tampering into an

optimal-rate -- i.e., rate 1 -- non-malleable codes against the same class.

If the original code is explicit, so is the new one.

When applied to the family of bit-wise tampering functions, this subsumes

(and greatly simplifies) a recent result of Cheraghchi and Guruswami (TCC

2014). Further, our compiler can be applied to non-malleable codes against

the class of bit-wise tampering and bit-level permutations. Combined with

the rate-0 construction in a companion work, this yields the first explicit

rate-1 non-malleable code for this family of tampering functions.

Our compiler uses a new technique for boot-strapping non-malleability by

introducing errors, that may be of independent interest.