| Abstract | In synchronous networks, protocols can achieve security guarantees that are not possible in an asynchronousworld: 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 syn-
chronous 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.
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