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We describe a defense against zeroizing attacks on indistinguishability obfuscation (iO) over the CLT13 multilinear map construction that only causes an additive blowup in the size of the branching program. This defense even applies to the most recent extension of the attack by Coron et al. (PKC 2017), under which a much larger class of branching programs is vulnerable. To accomplish this, we describe an attack model for the current attacks on iO over CLT13 by distilling an essential common component of all previous attacks.

This essential component is a constraint on the function being obfuscated. We say the function needs to be input partionable, meaning that the bits of the function’s input can be partitioned into somewhat independent subsets. This notion constitutes an attack model which we show captures all known attacks on obfuscation over CLT13. We find a way to thwart these attacks …