With the rapid evolution and diversification of Internet applications, their communication-quality criteria are continuously evolving. To globally optimize communication quality, the Internet's control plane thus needs to optimize inter-domain paths on diverse criteria, and should provide extensibility for adding new criteria or modifying existing ones. However, current inter-domain routing protocols and proposals satisfy these requirements at best to a limited degree.

To realize the long-standing vision of providing quality-of-service (QoS) guarantees on a public Internet, this paper introduces Hummingbird: a lightweight QoS-system that provides fine-grained inter-domain reservations for end hosts.

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.

We instigate the study of adversarial congestion in the context of the Domain Name System (DNS). By strategically choking inter-server channels, this new type of DoS attack can disrupt a large user group's access to target DNS servers at a low cost. In reminiscence of classic network congestion control, we propose a DNS congestion control (DCC) framework as a fundamental yet practical mitigation measure for such attacks. With an optimized fair-queuing message scheduler, DCC ensures benign clients fair access to inter-server channels regardless of an attacker's behavior; with a set of extensible anomaly detection and signaling mechanisms, it minimizes collateral damage to innocuous clients. We architect DCC in a non-invasive style so that it can readily augment existing DNS servers. Our prototype evaluation demonstrates that DCC effectively mitigates adversarial congestion while incurring minor performance overheads.

To protect against naturally occurring or adversely induced congestion in the Internet, we propose the concept of flyover reservations, a fundamentally new approach for addressing the availability demands of critical low-volume applications. In contrast to path-based reservation systems, flyovers are fine-grained "hop-based" bandwidth reservations on the level of individual autonomous systems. We demonstrate the scalability of this approach experimentally through simulations on large graphs. Moreover, we bring the flyovers' potential to full fruition by introducing Helia, a protocol for secure flyover reservation setup and data transmission. We evaluate Helia's performance based on an implementation in DPDK, demonstrating authentication and forwarding of reservation traffic at 160 Gbps. Our security analysis shows that Helia can resist a large variety of powerful attacks against reservation admission and traffic forwarding. Despite its simplicity, Helia outperforms current state-of-the-art reservation systems in many key metrics.

In recent years, much progress has been made in the field of Internet bandwidth reservation systems. While early designs were neither secure nor scalable, newer proposals promise attack resilience and Internet-wide scalability by using cryptographic access tokens (capabilities) that represent permissions to send at a guaranteed rate. Once a capability-based bandwidth reservation is established, the corresponding traffic is protected from both naturally occurring congestion and distributed denialof-service attacks, with positive consequences on the end-to-end quality of service (QoS) of the communication. However, high network utilization—possibly caused by adversaries—can still preclude the initial unprotected establishment of capabilities. To prevent such denial-of-capability (DoC) attacks, we present DoCile, a framework for the protection of capability establishment on Internet paths, irrespective of network utilization. We believe that DoCile, deployed alongside a capability-based bandwidth reservation system, can be the foundation of the next generation of secure and scalable QoS protocols.

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.

Guarantees for traffic traversing the public Internet are hard to come by, as service-level agreements are typically only available for traffic within a single autonomous system or towards direct neighbors. This deficiency leads to unpredictable performance already under normal conditions and can cause outages in the face of networklevel distributed-denial-of-service (DDoS) attacks. In this paper, we present an architecture achieving guaranteed bandwidth properties for global inter-domain network traffic. The control plane of our architecture is based on a distributed server infrastructure, while the data plane enables efficient packet forwarding on per-flow stateless routers. Our implementation demonstrates the technical feasibility and scalability of the design.

With the proliferation of online payment systems, the emergence of globally distributed consensus algorithms, and the increase of remotely managed critical IoT infrastructure, the need for critical-yet-frugal communication—high-availability and low-rate—is becoming increasingly pressing. For many of these applications, the use of leased lines or SD-WAN solutions is impractical due to their inflexibility and high costs, while standard Internet communication lacks the necessary reliability and attack resilience.To address this rising demand for strong quality-of-service (QoS) guarantees, we develop the GMA-based light-weight communication protocol (GLWP), building on a recent theoretical result, the GMA algorithm. GLWP is a capability-based protocol which is able to bootstrap network-wide bandwidth allocations in single round-trip times, and achieves high availability even under active attacks. Due to its clever use of cryptographic mechanisms, GLWP introduces minimal state in the network and causes low computation and communication overhead. We implement a GLWP prototype using Intel DPDK and show that it achieves line rate on a 40 Gbps link running on commodity hardware, thus showing that GLWP is a viable solution to provide strong QoS guarantees for critical-yet-frugal communications.

Novel interactions that capacitively couple electromagnetic (EM) fields between devices and the human body are gaining more attention in the human-computer interaction community. One class of these techniques is Body Channel Communication (BCC), a method that overlays physical touch with digital information. Despite the number of published capacitive sensing and communication prototypes, there exists no guideline on how to design such hardware or what are the application limitations and possibilities. Specifically, wearable (groundless) BCC has been proven in the past to be extremely challenging to implement. Additionally, the exact behavior of the human body as an EM-field medium is still not fully understood today. Consequently, the application domain of BCC technology could not be fully explored. This paper addresses this problem. Based on a recently published general purpose wearable BCC system, we first present a thorough evaluation of the impact of various technical parameter choices and an exhaustive channel characterization of the human body as a host for BCC. Second, we discuss the implications of these results for the application design space and present guidelines for future wearable BCC systems and their applications. Third, we point out an important observation of the measurements, namely that BCC can employ the whole body as user interface (and not just hands or feet). We sketch several applications with these novel interaction modalities.