# [Busec] Vassilis Zikas - Today 10:30-12

Ran Canetti canetti at tau.ac.il
Thu Oct 13 09:18:02 EDT 2011

Reminder:

BU CS building (111 Cummington st) Room 137
10:30-12

Title: Secure Computation with Corruptible Setups

Vassilis Zikas, UMD

Abstract:
Universally composable (UC) protocols satisfy strong and
desirable security properties. Unfortunately, soon after the
introduction of the UC framework it was shown that in the
plain'' model most cryptographic tasks cannot be realized
without an honest majority. Researchers since then have
therefore proposed various forms of trusted setup'', and have
shown many setups that are \emph{complete} and can thus be
leveraged to securely carry out any desired task.

With only a few notable exceptions, past work has viewed these
setup assumptions as being implemented by some ideal,
incorruptible entity. In reality, however, setups would likely
be carried out by some mechanism that could be subverted, or by
some party that could be compromised. Most prior work provides
no guarantees in such cases.

We propose here a clean, general, and generic approach for
modeling potential corruption of setups within the UC
framework, where such corruption might be fail-stop, passive,
or arbitrary and is in addition to possible corruption of the
parties. We also show several results regarding feasibility in
this model for these corruption types (and their combinations)  for
different specifications of the corruptible sets. For example, we show
that given $m$ complete setups, any $t$ of which might be
actively corrupted, general secure computation is possible iff
$t<m/2$ even when arbitrarily many parties are actively corrupted.

This is joint work with Jonathan Katz, Aggelos Kiayias, and Hong-Sheng Zhou.

---------------------------------------------------------------------------
>>>> Title: Universally Composable Synchronous Computation
>>>>
>>> Abstract.
>>>>
>>>> In synchronous networks, protocols can achieve security guarantees that
>>>> are not possible in an asynchronous world: i.e., they can simultaneously
>>>> achieve input completeness (all honest parties' inputs are included in
>>>> the computation) and guaranteed termination (honest parties do not
>>>> "hang" indefinitely). In practice truly synchronous networks rarely
>>>> exist, but synchrony can be emulated if channels have (known) latency
>>>> and parties have loosely synchronized clocks.
>>>>
>>>> The framework of universal composability (UC) is inherently
>>>> asynchronous, but several approaches for adding synchrony to the
>>>> framework have been proposed. However, we show that the existing
>>>> proposals do not provide the expected guarantees. Given this, we propose
>>>> a "clean slate" approach to defining synchrony in the UC framework by
>>>> introducing functionalities exactly meant to model, respectively,
>>>> bounded-delay networks and loosely synchronized clocks. We show that the
>>>> expected guarantees of synchronous computation can be realized given
>>>> these functionalities, and that previous models can all be expressed
>>>> within our new framework.
>>>>
>>>> This is joint work with Jonathan Katz, Ueli Maurer, and Bjoern
>>>> Tackmann.
>>>> ------------------------------------------------------------------------------------

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