International Association for Cryptologic Research

International Association
for Cryptologic Research

IACR News item: 27 February 2015

Saikrishna Badrinarayanan, Eric Miles, Amit Sahai, Mark Zhandry
ePrint Report ePrint Report
Recent devastating attacks by Cheon et al. [Eurocrypt\'15] and others have highlighted significant gaps in our intuition about security in candidate multilinear map schemes, and in candidate

obfuscators that use them. The new attacks, and some that were previously known, are typically called \"zeroizing\" attacks because they all crucially rely on the ability of the adversary to create

encodings of 0.

In this work, we initiate the study of post-zeroizing obfuscation, and we present a construction for the special case of evasive functions. We show that our obfuscator survives all known attacks

on the underlying multilinear maps, by proving that no encodings of 0 can be created by a generic-model adversary. Previous obfuscators (for both evasive and general functions) were either analyzed in a less-conservative \"pre-zeroizing\" model that does not capture recent attacks, or were proved secure relative to assumptions that are now known to be false.

To prove security, we introduce a new technique for analyzing polynomials over multilinear map encodings. This technique shows that the types of encodings an adversary can create are much more restricted than was previously known, and is a crucial step toward achieving postzeroizing security. We also believe the technique is of independent interest, as it yields efficiency improvements for existing schemes.

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