On UC Security, Deniability and Global Setup
Speaker: Yevgeniy Dodis , New York University
Date: November 2 2007
Time: 10:30AM to 12:00PM
Location: 32-G449, Patil/Kiva
Contact: Be Blackburn, 3-6098, imbe@mit.edu
Relevant URL: http://eprint.iacr.org/2006/432
In this talk we extend the Universal Composability (UC) framework to
properly model global setup, such as Common Reference String (CRS),
Public-Key Infrastructure (PKI) and Random Oracle (RO) models. The
new, Generalized UC (GUC) framework has many advatages over the
traditional UC framework.
1) it gurantees deniability. 2) it allows one to use the same setup
with *arbitrary* protocols, as opposed to specially designed protocols
(as in ordinary UC).
3) it is more natural than UC. For example, it
removes artificial restrictions of the former, resulting in shorter
definitions.
4) one can still model UC setup in GUC, but the resulting setup
assumptions become very hard to realize. This explains several
existing criticisms of the UC modeling of the CRS/PKI models.
We also show that the global CRS model in insufficient to realize most
useful tasks in GUC. However, we introduce a slight strengthing of the
CRS setup --- augmented CRS (ACRS) --- which allows one to GUC-realize
any cryptographic task. This novel setup (necessarily) introduces a
semi-passive trusted party into the CRS model, but has the following
win-win guarantee: if the trusted party is present, we get (very
strong) GUC security; if it is not, we get a functional equivalent of
the CRS model in the UC framework, but with provably stronger security
guarantees!
The paper is available at http://eprint.iacr.org/2006/432
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