| Abstract | We provide the first standard model construction for a powerful class of Universal Computational Extractors (UCEs; Bellare et al. Crypto 2013) based on indistinguishability obfuscation.
Our construction suffices to instantiate q-query correlation-secure hash functions and to extract
polynomially many hardcore bits from any one-way function.
For many cryptographic primitives and in particular for correlation-secure hash functions all known
constructions are in the random-oracle model. Indeed, recent negative results by Wichs (ITCS 2013)
rule out a large class of techniques to prove the security of correlation-secure hash functions in
the standard model. Our construction is based on puncturable PRFs (Sahai und Waters; STOC
2014) and indistinguishability obfuscation. However, our proof also relies on point obfuscation under
auxiliary inputs (AIPO). This is crucial in light of Wichs’ impossibility result. Namely, Wichs proves
that it is often hard to reduce two-stage games (such as UCEs) to a “one-stage assumption” such
as DDH. In contrast, AIPOs and their underlying assumptions are inherently two-stage and, thus,
allow us to circumvent Wichs’ impossibility result.
Our positive result is also noteworthy insofar as Brzuska, Farshim and Mittelbach (Crypto 2014)
have shown recently, that iO and some variants of UCEs are mutually exclusive. Our results, hence,
validate some of the new UCE notions that emerged as a response to the iO-attack. |
|---|
