Joel Wanner

Fabio Streun, Joel Wanner, Adrian Perrig

Many systems today rely heavily on virtual private network (VPN) technology to connect networks and protect their services on the Internet. While prior studies compare the performance of different implementations, they do not consider adversarial settings. To address this gap, we evaluate the resilience of VPN implementations to flooding-based denial-of-service (DoS) attacks. We focus on a class of stateless flooding attacks, which are particularly threatening to real connections, as they can be carried out by an off-path attacker using spoofed IP addresses. We have implemented various attacks to evaluate DoS resilience for three major open-source VPN solutions, with surprising results: On high-performance hardware with a $40\,\mathrm{Gb/s}$ interface, data transfer over established WireGuard connections can be fully denied with $700\,\mathrm{Mb/s}$ of attack traffic. For strongSwan (IPsec), an adversary can block any legitimate connections from being established using only $75\,\mathrm{Mb/s}$ of attack traffic. OpenVPN can be overwhelmed with $100\,\mathrm{Mb/s}$ of flood traffic denying data transfer through the VPN connection as well as connection establishment completely. Further analysis has revealed implementation bugs and major inefficiencies in the implementations related to concurrency aspects. These findings demonstrate a need for more adversarial testing of VPN implementations with respect to DoS resilience.

Joel Wanner, Laurent Chuat, Adrian Perrig

Byzantine fault tolerant protocols enable state replication in the presence of crashed, malfunctioning, or actively malicious processes. Designing such protocols without the assistance of verification tools, however, is remarkably error-prone. In an adversarial environment, performance and flexibility come at the cost of complexity, making the verification of existing protocols extremely difficult. We take a different approach and propose a formally verified consensus protocol designed for a specific use case: secure logging. Our protocol allows each node to propose entries in a parallel subroutine, and guarantees that correct nodes agree on the set of all proposed entries, without leader election. It is simple yet practical, as it can accommodate the workload of a logging system such as Certificate Transparency. We show that it is optimal in terms of both required rounds and tolerable faults. Using Isabelle/HOL, we provide a fully machine-checked security proof based upon the Heard-Of model, which we extend to support signatures. We also present and evaluate a prototype implementation.