We present a framework for proving meaningful negative results on the power of indistinguishability obfuscation. By considering indistinguishability obfuscation for oracle-aided circuits, we capture the common techniques that have been used so far in constructions based on indistinguishability obfuscation. These include, in particular, non-black-box techniques such as the punctured programming approach of Sahai and Waters (STOC '14) and its variants, as well as sub-exponential security assumptions.
Within our framework we prove the first negative results on the power of indistinguishability obfuscation and of the tightly related notion of functional encryption. Our results are as follows:
-- There is no fully black-box construction of a collision-resistant function family from an indistinguishability obfuscator for oracle-aided circuits.
-- There is no fully black-box construction of a key-agreement protocol with perfect completeness from a private-key functional encryption scheme for oracle-aided circuits.
Specifically, we prove that any such potential constructions must suffer from an exponential security loss, and thus our results cannot be circumvented using sub-exponential security assumptions. Our framework captures constructions that may rely on a wide variety of primitives in a non-black-box manner (e.g., obfuscating or generating a functional key for a function that uses the evaluation circuit of a puncturable pseudorandom function), and we only assume that the underlying indistinguishability obfuscator or functional encryption scheme themselves are used in a black-box manner.Category / Keywords: foundations / Original Publication (with major differences): FOCS 2015 Date: received 15 Apr 2015, last revised 28 Jul 2015 Contact author: segev at cs huji ac il Available format(s): PDF | BibTeX Citation Version: 20150729:052117 (All versions of this report) Short URL: ia.cr/2015/341 Discussion forum: Show discussion | Start new discussion