Zeroizing Attacks on Indistinguishability Obfuscation over CLT13

In this work, we describe a new polynomial-time attack on the multilinear maps of Coron, Lepoint, and Tibouchi (CLT13), when used in candidate iO schemes. More specifically, we show that given the obfuscation of the simple branching program that computes the always zero functionality previously considered by Miles, Sahai and Zhandry (Crypto 2016), one can recover the secret parameters of CLT13 in polynomial time via an extension of the zeroizing attack of Coron et al. (Crypto 2015). Our attack is generalizable to arbitrary oblivious branching programs for arbitrary functionality, and allows (1) to recover the secret parameters of CLT13, and then (2) to recover the randomized branching program entirely. Our analysis thus shows that several of the single-input variants of iO over CLT13 are insecure.