On Strong Simulation and Composable Point Obfuscation
Speaker: Nir Bitansky , Tel-Aviv University
Date: August 13 2010
Time: 10:30AM to 12:00PM
Location: 32-G449 Patil/Kiva
Host: Ran Canetti, CSAIL, MIT
Contact: Be Blackburn , 3-6098, imbe@mit.edu
Relevant URL: The Virtual Black Box (VBB) property for program obfuscators
provides a strong guarantee: Anything computable by an efficient
adversary given the obfuscated program can also be computed by an
efficient simulator with only oracle access to the program. However,
we know how to achieve this notion only for very restricted classes
of programs.
This work studies a simple relaxation of VBB: Allow the simulator
unbounded computation time, while still allowing only polynomially
many queries to the oracle. We then demonstrate the viability of
this relaxed notion, which we call Virtual Grey Box (VGB), in the
context of fully composable obfuscators for point programs: It is
known that, w.r.t. VBB, if such obfuscators exist then there exist
multi-bit point obfuscators (aka ``digital lockers'') and
subsequently also very strong variants of encryption that are
resilient to various attacks, such as key leakage and
key-dependent-messages.
However, no composable VBB-obfuscators for point programs have been
shown. We show fully composable {\em VGB}-obfuscators for point
programs under a strong variant of the Decision Diffie Hellman
assumption. We show they suffice for the above applications and even
for extensions to the public key setting as well as for encryption
schemes with resistance to certain related key attacks (RKA).
Joint work with Ran Canetti.
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