TY - GEN A1 - Pennekamp, Jan A1 - Hiller, Jens A1 - Reuter, Sebastian A1 - De la Cadena, Wladimir A1 - Mitseva, Asya A1 - Henze, Martin A1 - Engel, Thomas A1 - Wehrle, Klaus A1 - Panchenko, Andriy T1 - Multipathing Traffic to Reduce Entry Node Exposure in Onion Routing T2 - Proceedings of the 27th annual IEEE International Conference on Network Protocols (Poster) (IEEE ICNP 2019), Chicago, Illinois, USA, October 2019 N2 - Users of an onion routing network, such as Tor, depend on its anonymity properties. However, especially malicious entry nodes, which know the client’s identity, can also observe the whole communication on their link to the client and, thus, conduct several de-anonymization attacks. To limit this exposure and to impede corresponding attacks, we propose to multipath traffic between the client and the middle node to reduce the information an attacker can obtain at a single vantage point. To facilitate the deployment, only clients and selected middle nodes need to implement our approach, which works transparently for the remaining legacy nodes. Furthermore, we let clients control the splitting strategy to prevent any external manipulation. Y1 - 2019 UR - https://ieeexplore.ieee.org/document/8888029 SN - 978-1-7281-2700-2 SN - 978-1-7281-2701-9 U6 - https://doi.org/10.1109/ICNP.2019.8888029 SN - 2643-3303 SN - 1092-1648 PB - IEEE Press ER - TY - GEN A1 - Hiller, Jens A1 - Pennekamp, Jan A1 - Dahlmanns, Markus A1 - Henze, Martin A1 - Panchenko, Andriy A1 - Wehrle, Klaus T1 - Tailoring Onion Routing to the Internet of Things: Security and Privacy in Untrusted Environments T2 - Proceedings of the 27th annual IEEE International Conference on Network Protocols (IEEE ICNP 2019), Chicago, Illinois, USA, October 2019 N2 - An increasing number of IoT scenarios involve mobile, resource-constrained IoT devices that rely on untrusted networks for Internet connectivity. In such environments, attackers can derive sensitive private information of IoT device owners, e.g., daily routines or secret supply chain procedures, when sniffing on IoT communication and linking IoT devices and owner. Furthermore, untrusted networks do not provide IoT devices with any protection against attacks from the Internet. Anonymous communication using onion routing provides a well-proven mechanism to keep the relationship between communication partners secret and (optionally) protect against network attacks. However, the application of onion routing is challenged by protocol incompatibilities and demanding cryptographic processing on constrained IoT devices, rendering its use infeasible. To close this gap, we tailor onion routing to the IoT by bridging protocol incompatibilities and offloading expensive cryptographic processing to a router or web server of the IoT device owner. Thus, we realize resource-conserving access control and end-toend security for IoT devices. To prove applicability, we deploy onion routing for the IoT within the well-established Tor network enabling IoT devices to leverage its resources to achieve the same grade of anonymity as readily available to traditional devices. KW - Routing, Internet of Things, Protocols, Cryptography, Servers Y1 - 2019 UR - https://ieeexplore.ieee.org/document/8888033 SN - 978-1-7281-2700-2 SN - 978-1-7281-2701-9 U6 - https://doi.org/10.1109/ICNP.2019.8888033 SN - 2643-3303 SN - 1092-1648 PB - IEEE Press ER - TY - GEN A1 - De La Cadena, Wladimir A1 - Mitseva, Asya A1 - Pennekamp, Jan A1 - Hiller, Jens A1 - Lanze, Fabian A1 - Engel, Thomas A1 - Wehrle, Klaus A1 - Panchenko, Andriy T1 - POSTER: Traffic Splitting to Counter Website Fingerprinting T2 - CCS '19 Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Security , London, UK, November 11 - 15, 2019. N2 - Website fingerprinting (WFP) is a special type of traffic analysis, which aims to infer the websites visited by a user. Recent studies have shown that WFP targeting Tor users is notably more effective than previously expected. Concurrently, state-of-the-art defenses have been proven to be less effective. In response, we present a novel WFP defense that splits traffic over multiple entry nodes to limit the data a single malicious entry can use. Here, we explore several traffic-splitting strategies to distribute user traffic. We establish that our weighted random strategy dramatically reduces the accuracy from nearly 95% to less than 35% for four state-of-the-art WFP attacks without adding any artificial delays or dummy traffic. Y1 - 2019 UR - https://dl.acm.org/citation.cfm?doid=3319535.3363249 SN - 978-1-4503-6747-9 U6 - https://doi.org/10.1145/3319535.3363249 SP - 2533 EP - 2535 PB - ACM Press CY - New York ER - TY - GEN A1 - Holz, Ralph A1 - Hiller, Jens A1 - Amann, Johanna A1 - Razaghpanah, Abbas A1 - Jost, Thomas A1 - Vallina-Rodriguez, Narseo A1 - Hohlfeld, Oliver T1 - Tracking the deployment of TLS 1.3 on the Web: A story of experimentation and centralization T2 - ACM SIGCOMM Computer Communication Review Y1 - 2020 U6 - https://doi.org/10.1145/3411740.3411742 SN - 0146-4833 VL - 50 IS - 3 ER - TY - GEN A1 - Hiller, Jens A1 - Amann, Johanna A1 - Hohlfeld, Oliver T1 - The Boon and Bane of Cross-Signing: Shedding Light on a Common Practice in Public Key Infrastructures T2 - CCS '20: Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security, October 2020 N2 - Public Key Infrastructures (PKIs) with their trusted Certificate Authorities (CAs) provide the trust backbone for the Internet: CAs sign certificates which prove the identity of servers, applications, or users. To be trusted by operating systems and browsers, a CA has to undergo lengthy and costly validation processes. Alternatively, trusted CAs can cross-sign other CAs to extend their trust to them. In this paper, we systematically analyze the present and past state of cross-signing in the Web PKI. Our dataset (derived from passive TLS monitors and public CT logs) encompasses more than 7 years and 225 million certificates with 9.3 billion trust paths. We show benefits and risks of cross-signing. We discuss the difficulty of revoking trusted CA certificates where, worrisome, cross-signing can result in valid trust paths to remain after revocation; a problem for non-browser software that often blindly trusts all CA certificates and ignores revocations. However, cross-signing also enables fast bootstrapping of new CAs, e.g., Let's Encrypt, and achieves a non-disruptive user experience by providing backward compatibility. In this paper, we propose new rules and guidance for cross-signing to preserve its positive potential while mitigating its risks. KW - Security and privacy KW - Network security Y1 - 2020 U6 - https://doi.org/10.1145/3372297.3423345 SP - 1289 EP - 1306 ER - TY - GEN A1 - De la Cadena, Wladimir A1 - Mitseva, Asya A1 - Hiller, Jens A1 - Pennekamp, Jan A1 - Reuter, Sebastian A1 - Filter, Julian A1 - Engel, Thomas A1 - Wehrle, Klaus A1 - Panchenko, Andriy T1 - TrafficSliver: Fighting Website Fingerprinting Attacks with Traffic Splitting T2 - CCS '20: Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security, October 2020 N2 - Website fingerprinting (WFP) aims to infer information about the content of encrypted and anonymized connections by observing patterns of data flows based on the size and direction of packets. By collecting traffic traces at a malicious Tor entry node — one of the weakest adversaries in the attacker model of Tor — a passive eavesdropper can leverage the captured meta-data to reveal the websites visited by a Tor user. As recently shown, WFP is significantly more effective and realistic than assumed. Concurrently, former WFP defenses are either infeasible for deployment in real-world settings or defend against specific WFP attacks only. To limit the exposure of Tor users to WFP, we propose novel lightweight WFP defenses, TrafficSliver, which successfully counter today’s WFP classifiers with reasonable bandwidth and latency overheads and, thus, make them attractive candidates for adoption in Tor. Through user-controlled splitting of traffic over multiple Tor entry nodes, TrafficSliver limits the data a single entry node can observe and distorts repeatable traffic patterns exploited by WFP attacks.We first propose a network-layer defense, in which we apply the concept of multipathing entirely within the Tor network. We show that our network-layer defense reduces the accuracy from more than 98% to less than 16% for all state-of-the-art WFP attacks without adding any artificial delays or dummy traffic. We further suggest an elegant client-side application-layer defense, which is independent of the underlying anonymization network. By sending single HTTP requests for different web objects over distinct Tor entry nodes, our application-layer defense reduces the detection rate of WFP classifiers by almost 50 percentage points. Although it offers lower protection than our network-layer defense, it provides a security boost at the cost of a very low implementation overhead and is fully compatible with today's Tor network. KW - Traffic Analysis KW - Website Fingerprinting KW - Privacy KW - Anonymous Communication KW - Onion Routing KW - Web Privacy Y1 - 2020 SN - 978-1-4503-7089-9 U6 - https://doi.org/10.1145/3372297.3423351 SP - 1971 EP - 1985 PB - Association for Computing Machinery CY - New York ER - TY - GEN A1 - Hiller, Jens A1 - Henze, Martin A1 - Zimmermann, Torsten A1 - Hohlfeld, Oliver A1 - Wehrle, Klaus T1 - The Case for Session Sharing: Relieving Clients from TLS Handshake Overheads T2 - 2019 IEEE 44th LCN Symposium on Emerging Topics in Networking (LCN Symposium), 14-17 Oct. 2019, Osnabrück, Germany N2 - In recent years, the amount of traffic protected with Transport Layer Security (TLS) has significantly increased and new protocols such as HTTP/2 and QUIC further foster this emerging trend. However, protecting traffic with TLS has significant impacts on network entities. While the restrictions for middleboxes have been extensively studied, addressing the impact of TLS on clients and servers has been mostly neglected so far. Especially mobile clients in emerging 5G and IoT deployments suffer from significantly increased latency, traffic, and energy overheads when protecting traffic with TLS. In this paper, we address this emerging topic by thoroughly analyzing the impact of TLS on clients and servers and derive opportunities for significantly decreasing latency of TLS communication and downsizing TLS management traffic, thereby also reducing TLSinduced server load. We propose a protocol compatible redesign of TLS session management to use these opportunities and showcase their potential based on mobile device traffic and mobile web-browsing traces. These show promising potentials for latency improvements by up to 25.8% and energy savings of up to 26.3%. KW - TLS Performance, Efficient Secure Communication, TLS Session Resumption, Network Security, Security and Privacy, Mobile Networking, 5G and IoT Y1 - 2019 UR - https://ieeexplore.ieee.org/document/9000667 SN - 978-1-7281-2561-9 SN - 978-1-7281-2562-6 U6 - https://doi.org/10.1109/LCNSymposium47956.2019.9000667 PB - IEEE ER - TY - GEN A1 - Reuter, Sebastian A1 - Hiller, Jens A1 - Pennekamp, Jan A1 - Panchenko, Andriy A1 - Wehrle, Klaus T1 - Demo: Traffic Splitting for Tor – A Defense against Fingerprinting Attacks T2 - Conference on Networked Systems 2021 (NetSys 2021) N2 - Website fingerprinting (WFP) attacks on the anonymity network Tor have become ever more effective. Furthermore, research discovered that proposed defenses are insufficient or cause high overhead. In previous work, we presented a new WFP defense for Tor that incorporates multipath transmissions to repel malicious Tor nodes from conducting WFP attacks. In this demo, we showcase the operation of our traffic splitting defense by visually illustrating the underlying Tor multipath transmission using LED-equipped Raspberry Pis. KW - Onion Routing; Website Fingerprinting; Multipath Traffic; Privacy Y1 - 2021 U6 - https://doi.org/10.14279/tuj.eceasst.80.1151.1128 SN - 1863-2122 ER -