IACR News item: 19 April 2015
Gilad Asharov, Gil Segev
ePrint Report-- There is no fully black-box construction with a polynomial security loss of a collision-resistant function family from a general-purpose indistinguishability obfuscator.
-- There is no fully black-box construction with a polynomial security loss of a key-agreement protocol with perfect completeness from a general-purpose private-key functional encryption scheme.
-- There is no fully black-box construction with a polynomial security loss of an indistinguishability obfuscator for oracle-aided circuits from a private-key functional encryption scheme for oracle-aided circuits.
Specifically, we prove that any such potential construction must suffer from at least a sub-exponential security loss. Our results are obtained within a subtle framework capturing 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.
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