Limits on the Locality of Pseudorandom Generators and Applications to Indistinguishability Obfuscation

Abstract

© 2017, International Association for Cryptologic Research. Lin and Tessaro (ePrint 2017) recently proposed indistinguishability obfuscation (IO) and functional encryption (FE) candidates and proved their security based on two assumptions: a standard assumption on bilinear maps and a non-standard assumption on “Goldreich-like” pseudorandom generators. In a nutshell, their second assumption requires the existence of pseudorandom generators G:[q] n → {0,1} m for some poly(n) -size alphabet q, each of whose output bits depend on at most two in put alphabet symbols, and which achieve sufficiently large stretch. We show polynomial-time attacks against such generators, invalidating the security of the IO and FE candidates. Our attack uses tools from the literature on two-source extractors (Chor and Goldreich, SICOMP 1988) and efficient refutation of random 2-XOR instances (Charikar and Wirth, FOCS 2004).