Numerous vital applications depend on accurately synchronized time, and disruptions can yield severe consequences in terms of safety and security. Yet, establishing cost-efficient and robust synchronization across geographically distributed devices is challenging. Many solutions for global time synchronization require placing trust in a single entity or system, for example in Global Navigation Satellite Systems (G NSSes) or leased infrastructure providers, constituting a single point of failure and often incurring high costs. An alternative, cost-effective solution is to run time synchronization over the Internet. However, this approach faces challenges in achieving (i) precise time synchronization, (ii) robustness to failing, misconfigured, or compromised nodes, and (iii) robustness to congestion-related issues such as volumetric DDoS attacks. Existing proposals mostly attempt to solve challenges (i) and (ii), but none provide robustness against congestion and volumetric DDoS. We address the challenges identified in previous work with Everdeen. Everdeen minimizes costs by running on existing Internet infrastructure and avoids relying on any single en-tity by enabling nodes to mutually synchronize time. The core innovation of Everdeen is its weighted neighbor-based (WNB) synchronization mode, where participants synchronize exclusively with their direct neighbors. Our evaluation shows that Everdeen provides better time synchronization quality at lower communication overhead compared to prior work. It is also considerably more robust against failing, misconfigured, or compromised hosts. Most importantly, we experimentally demonstrate that time synchronization traffic protected with Everdeen is unaffected by network congestion, including vol-umetric DDoS attacks.

With the proliferation of blockchain technology in high-value sectors, consensus protocols are becoming critical infrastructures. The rapid innovation cycle in Byzantine fault tolerant (BFT) consensus protocols has culminated in HotStuff, which provides linear message complexity in the partially synchronous setting. To achieve this, HotStuff leverages a leader that collects, aggregates, and broadcasts the messages of other validators. This paper analyzes the security implications of such approaches in practice, from the perspective of liveness and availability.

Many critical computing applications rely on secure and dependable time which is reliably synchronized across large distributed systems. Today's time synchronization architectures are commonly based on global navigation satellite systems at the considerable risk of being exposed to outages, malfunction, or attacks against availability and accuracy. This paper describes a practical instantiation of a new global, Byzantine fault-tolerant clock synchronization approach that does not place trust in any single entity and is able to tolerate a fraction of faulty entities while still maintaining synchronization on a global scale among otherwise sovereign network topologies. Leveraging strong resilience and security properties provided by the path-aware SCION networking architecture, the presented design can be implemented as a backward compatible active standby solution for existing time synchronization deployments. Through extensive evaluation, we demonstrate that over 94 % of time servers reliably minimize the offset of their local clocks to real-time in the presence of up to 20 % malicious nodes, and all time servers remain synchronized with a skew of only 2 ms even after one year of reference clock outage.