[Busec] busec this week: Vinod Vaikuntanathan (Wed 9.30am)

Sharon Goldberg goldbe at cs.bu.edu
Sun Dec 7 22:45:07 EST 2014

We are very excited to have Vinod Vaikuntanathan from MIT give our final
seminar for the semester, this Wed Dec 10.  We will start slightly earlier
(9.30am) this week.

Abstract below.


BUsec Calendar:  http://www.bu.edu/cs/busec/
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The busec seminar gratefully acknowledges the support of BU's Center for
Reliable Information Systems and Cyber Security (RISCS).

The Trojan Method in Functional Encryption: From Selective to Adaptive
Security, Generically
Vinod Vaikuntanathan, MIT.
Wed. Dec. 10, 2014, 9.30-11am
MCS 180, 111 Cummington Mall, Boston MA

In a functional encryption (FE) scheme, the owner of the secret key can
generate restricted decryption keys that allow users to learn specific
functions of the encrypted messages and nothing else. In many known
constructions of FE schemes, such a notion of security is guaranteed only
for messages that are fixed ahead of time (i.e., before the adversary even
interacts with the system). This is called selective security, which is too
restrictive for many realistic applications. Achieving adaptive security
(also called full security), where security is guaranteed even for messages
that are adaptively chosen at any point in time, seems significantly more
challenging. The handful of known fully-secure schemes are based on
specifically tailored techniques that rely on strong assumptions (such as
obfuscation assumptions or multilinear maps assumptions).

In this paper we show that any sufficiently expressive selectively-secure
FE scheme can be transformed into a fully secure one without introducing
any additional assumptions. We present a direct black-box transformation,
making novel use of hybrid encryption, a classical technique that was
originally introduced for improving the efficiency of encryption schemes,
combined with a new technique we call the Trojan Method. This method allows
to embed a secret execution thread in the functional keys of the underlying
scheme, which will only be activated within the proof of security of the
resulting scheme.As another application of the Trojan Method, we show how
to construct functional encryption schemes for arbitrary circuits starting
from ones for shallow circuits (NC1 or even TC0).

Joint work with Prabhanjan Ananth, Zvika Brakerski and Gil Segev.
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