[Busec] Melissa Chase Wed @ noon

Leonid Reyzin reyzin at cs.bu.edu
Mon Oct 24 00:22:30 EDT 2011


Melissa will be visiting us and will give a talk on Wednesday:


Functional Re-encryption and Collusion-Resistant Obfuscation  ****


We introduce a natural cryptographic functionality called “functional
re-encryption”.  Informally, functional re-encryption allows an untrusted
server to transform a ciphertext encrypted for Alice into a ciphertext
encrypted for one of n recipients, *depending on the message*.  In
particular, a functional re-encryption function for a function F will
transform an encryption of message m intended for Alice into an encryption
of m intended for recipient F(m).****

 ****

In many settings, one might require that the program implementing the
functional re-encryption functionality should reveal as little as possible
about the input secret key SK and the function F.  Furthermore, in this
setting ideally we would obtain an even stronger guarantee: that this
information remains hidden even when some of the n recipients may be
corrupted. ****

 ****

To formalize these issues, we introduce the notion of “collusion-resistant
obfuscation” and define this notion with respect to average-case secure
obfuscation (Hohenberger et al. - TCC 2007).  We then note that, unlike most
previous positive results on average case obfuscation, this problem cannot
be solved in a straightforward way using fully homomorphic encryption.
However, we show that this notion of functional re-encryption can be
achieved for any function F with a polynomial-size domain, by providing a
direct construction from bilinear pairings.   ****


This is joint work with Nishanth Chandran and Vinod Vaikuntanathan****
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