[Busec] BUsec next week: Aggelos Kiayias (Mon 10AM) Angela Zottarel (Wed 10AM) and CryptoDay (Fri 10AM)

Sharon Goldberg goldbe at cs.bu.edu
Mon Nov 19 15:55:10 EST 2012


Next week will be a crypto triple-header.

On Monday 10AM, Aggelos Kiayias, from U Athens, will be speaking about
resource-based corruptions.

On Wednesday 10AM, our new group member Angela Zottarel will be giving
a practice talk for her ASIACRYPT presentation.

And finally....
Friday is Charles River Crypto with four amazing speakers (Salil
Vadhan, Daniel Wichs, Vinod V, and Ran Raz). We start at 10AM at the
Hariri Institute .

Happy Thanksgiving!

BUsec Calendar:  http://www.bu.edu/cs/busec/
BUsec Mailing list:  http://cs-mailman.bu.edu/mailman/listinfo/busec


Resource-based Corruptions and the Combinatorics of Hidden Diversity
Aggelos Kiayias (U. Athens & U. Connecticut)
Monday Nov 26, 10AM

Abstract. In the setting of cryptographic protocols, the corruption of
a party has traditionally been viewed as a simple, uniform and atomic
operation, where the adversary decides to get control over a party and
this party immediately gets corrupted. In this paper, motivated by the
fact that different players may require different resources to get
corrupted, we put forth the notion of resource-based corruptions,
where the adversary must invest some resources in order to corrupt

If the adversary has full information about the system configuration
then resource-based corruptions would provide no fundamental
difference from the standard corruption model. However, in a resource
“anonymous” setting, in the sense that such configuration is hidden
from the adversary, much is to be gained in terms of efficiency and

We showcase the power of such hidden diversity in the context of
secure multiparty computation (MPC) with resource-based corruptions
and prove that it can effectively be used to circumvent known
impossibility results. Specifically, if OPT is the corruption budget
that violates the completeness of MPC (the case when half or more of
the players are corrupted), we show that if hidden diversity is
available, the completeness of MPC can be made to hold against an
adversary with as much as a B · OPT budget, for any constant B > 1.
This result requires a suitable choice of parameters (in terms of
number of players and their hardness to corrupt), which we provide and
further prove other tight variants of the result when the said choice
is not available. Regarding efficiency gains, we show that hidden
diversity can be used to force the corruption threshold to drop from
1/2 to 1/3, in turn allowing the use of much more efficient
(information-theoretic) MPC protocols.

Among others, the talk will go into details regarding the modeling of
the corruption process, the abstraction of the corruption game as a
combinatorial problem, and the formalization
of the properties of inversion effort preserving functions and
hardness indistinguishability that are needed to model hidden
diversity in the setting of computational corruptions.

Joint work with Juan Garay, David Johnson, Moti Yung.


Title: Signature Schemes Secure against Hard-to-Invert Leakage
Speaker: Angela Zottarel, Aarhus
MCS137 at 10AM

Abstract: In the auxiliary input model an adversary is allowed to see
a computationally hard-to-invert function of the secret key.  The
auxiliary input model weakens the bounded leakage assumption commonly
made in leakage resilient cryptography as the hard-to-invert function
may information-theoretically reveal the entire secret key.
In this work, we propose the first constructions of digital signature
schemes that are secure in the auxiliary input model. Our main
contribution is a digital signature scheme that is secure against
chosen message attacks when given an exponentially hard-to-invert
function of the secret key. As a second contribution, we construct a
signature scheme that achieves security for random messages assuming
that the adversary is given a polynomial-time hard to invert function.
Here, polynomial-hardness is required even when given the entire
public-key – so called weak auxiliary input security.  We show that
such signature schemes readily give us auxiliary input secure
identification schemes.

Joint work with S. Faust, C. Hazay, J.B. Nielsen and P. S. Nordholt

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