Universal Composability From Essentially Any Trusted Setup
Mike Rosulek (
Abstract:
It is impossible to securely carry out general multi-party computation in
arbitrary network contexts like the Internet, unless protocols have access to
some trusted setup. In this work we classify the power of such trusted
(2-party) setup functionalities. We show that nearly every setup is either useless (ideal access to the setup is
equivalent to having no setup at all) or else complete (composably secure protocols
for all tasks exist in the presence
of the setup). We further argue that those setups which are neither complete
nor useless are highly unnatural.
The main technical contribution in this work is an almost-total
characterization of completeness for 2-party setups. Our characterization
treats setup functionalities as black-boxes, and therefore is the first work
to classify completeness of arbitrary
setup functionalities (i.e., randomized, reactive, and having behavior
that depends on the global security parameter).