In synchronous networks, protocols can achieve security guarantees that are not possible in an asynchronous world: 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 widely-used framework of universal composability (UC) is inherently asynchronous, but several approaches for adding synchrony to the framework have been proposed. In this talk I will give a high-level overview of the UC security definitions and discuss how to use it for arguing the security of synchronous protocols. I will show that existing proposals do not provide the expected guarantees and propose a novel approach to defining synchrony in the UC framework by introducing functionalities exactly meant to model bounded-delay networks and loosely synchronized clocks. I will further show that the expected guarantees of synchronous computation can be realized given these functionalities, and argue that previous models can all be expressed within this new framework.