Welcome on the homepage of the chair "Internet Technologies and Systems" of Prof. Dr. Christoph Meinel and his team. We like to inform you about our teaching and ongoing research activities in security, knowledge engineering, innovation and design thinking research.
The chair of Prof. Dr. Christoph Meinel offers courses in the following disciplines: Internet and Web Technologies, (Discrete) Mathematics and Logic, IT Security and Internet Security, Complexity Theory and Information Security as well as Design Thinking.
The research of the team of Prof. Dr. Christoph Meinel in the field of knowledge management and engineering focus on the challenging question, how to manage the mass of digital data, so-called "big data", from Internet and other sources in order to generate new knowledge.
Interconnecting embedded devices with the Internet leads to the so-called Internet of things (IoT). The Internet of things is envisioned to realize fascinating applications, such as smart cities, predictive maintenance, and precision agriculture. These applications will involve large numbers of embedded devices that communicate with each other and remote hosts.
The security challenges in this area are diverse. On the one hand, IoT devices can be attacked from the Internet. On the other hand, IoT devices are often deployed outdoors in hostile environments and communicate wirelessly. Consequently, IoT devices require protection against both remote and local attackers.
Presently, our research in this area focuses on preventing denial-of-sleep attacks. Such attacks deprive battery-powered IoT devices of entering low-power sleep modes so as to drain their charge.
While the IEEE 802.15.4 radio standard has many features that meet the requirements of Internet of things (IoT) applications, IEEE 802.15.4 leaves the whole issue of key management unstandardized. To address this gap, Krentz et al. proposed the Adaptive Key Establishment Scheme (AKES), which establishes session keys for use in IEEE 802.15.4 security. Yet, AKES does not cover all aspects of key management. In particular, AKES comprises no means for key revocation and rekeying. Moreover, existing protocols for key revocation and rekeying seem limited in various ways. In this paper, we hence propose a key revocation and rekeying protocol, which is designed to overcome various limitations of current protocols for key revocation and rekeying. For example, our protocol seems unique in that it routes around IEEE 802.15.4 nodes whose keys are being revoked. We succesfully implemented and evaluated our protocol using the Contiki-NG operating system and aiocoap.
Deep En-Route Filtering of Constrained Application Protocol (CoAP) Messages on 6LoWPAN Border Routers.Seidel, Felix; Krentz, Konrad-Felix; Meinel, Christoph (2019).
Devices on the IoT are usually battery-powered and have limited resources. Hence, energy-efficient and lightweight protocols were designed for IoT devices, such as the popular CoAP. Yet, CoAP itself does not include any defenses against denial-of-sleep attacks, which are attacks that aim at depriving victim devices of entering low-power sleep modes. For example, a denial-of-sleep attack against an IoT device that runs a CoAP server is to send plenty of CoAP messages to it, thereby forcing the IoT device to expend energy for receiving and processing these CoAP messages. All current security solutions for CoAP, namely DTLS, IPsec, and OSCORE, fail to prevent such attacks. To fill this gap, Seitz et al. proposed a method for filtering out inauthentic and replayed CoAP messages "en-route" on 6LoWPAN border routers. In this paper, we expand on Seitz et al.'s proposal in two ways. First, we revise Seitz et al.'s software architecture so that 6LoWPAN border routers can not only check the authenticity and freshness of CoAP messages, but can also perform a wide range of further checks. Second, we propose a couple of such further checks, which, as compared to Seitz et al.'s original checks, more reliably protect IoT devices that run CoAP servers from remote denial-of-sleep attacks, as well as from remote exploits. We prototyped our solution and successfully tested its compatibility with Contiki-NG's CoAP implementation.
Denial-of-Sleep Defenses for IEEE 802.15.4 Coordinated Sampled Listening (CSL).Krentz, Konrad-Felix; Meinel, Christoph in Computer Networks (2019). 148 60-71.
Coordinated sampled listening (CSL) is a standardized medium access control protocol for IEEE 802.15.4 networks. Unfortunately, CSL comes without any protection against so-called denial-of-sleep attacks. Such attacks deprive energy-constrained devices of entering low-power sleep modes, thereby draining their charge. Repercussions of denial-of-sleep attacks include long outages, violated quality-of-service guarantees, and reduced customer satisfaction. However, while CSL has no built-in denial-of-sleep defenses, there already exist denial-of-sleep defenses for a predecessor of CSL, namely ContikiMAC. In this paper, we make two main contributions. First, motivated by the fact that CSL has many advantages over ContikiMAC, we tailor the existing denial-of-sleep defenses for ContikiMAC to CSL. Second, we propose several security enhancements to these existing denial-of-sleep defenses. In effect, our denial-of-sleep defenses for CSL mitigate denial-of-sleep attacks significantly better, as well as protect against a larger range of denial-of-sleep attacks than the existing denial-of-sleep defenses for ContikiMAC.We show the soundness of our denial-of-sleep defenses for CSL both analytically, as well as empirically using a whole new implementation of CSL.
Denial-of-Sleep-Resilient Session Key Establishment for IEEE 802.15.4 Security: From Adaptive to Responsive.Krentz, Konrad-Felix; Meinel, Christoph; Graupner, Hendrik (2018).
Battery-powered and energy-harvesting IEEE 802.15.4 nodes are subject to so-called denial-of-sleep attacks. Such attacks generally aim at draining the energy of a victim device. Especially, session key establishment schemes for IEEE 802.15.4 security are susceptible to denial-of-sleep attacks since injected requests for session key establishment typically trigger energy-consuming processing and communication. Nevertheless, Krentz et al.’s Adaptive Key Establishment Scheme (AKES) for IEEE 802.15.4 security is deemed to be resilient to denial-of-sleep attacks thanks to its energy-efficient design and special defenses. However, thus far, AKES’ resilience to denial-of-sleep attacks was presumably never evaluated. In this paper, we make two contributions. First, we evaluate AKES’ resilience to denial-of-sleep attacks both theoretically and empirically. We particularly consider two kinds of denial-of-sleep attacks, namely HELLO flood attacks, as well as what we introduce in this paper as “yo-yo attacks”. Our key finding is that AKES’ denial-of-sleep defenses require trade-offs between denial-of-sleep resilience and the speed at which AKES adapts to topology changes. Second, to alleviate these trade-offs, we devise and evaluate new denial-of-sleep defenses. Indeed, our newly-devised denial-of-sleep defenses turn out to significantly accelerate AKES’ reaction to topology changes, without incurring much overhead nor sacrificing on security.
More Lightweight, yet Stronger 802.15.4 Security through an Intra-Layer Optimization.Krentz, Konrad-Felix; Meinel, Christoph; Graupner, Hendrik (2017).
802.15.4 security protects against the replay, injection, and eavesdropping of 802.15.4 frames. A core concept of 802.15.4 security is the use of frame counters for both nonce generation and anti-replay protection. While being functional, frame counters (i) cause an increased energy consumption as they incur a per-frame overhead of 4 bytes and (ii) only provide sequential freshness. The Last Bits (LB) optimization does reduce the per-frame overhead of frame counters, yet at the cost of an increased RAM consumption and occasional energy- and time-consuming resynchronization actions. Alternatively, the timeslotted channel hopping (TSCH) media access control (MAC) protocol of 802.15.4 avoids the drawbacks of frame counters by replacing them with timeslot indices, but findings of Yang et al. question the security of TSCH in general. In this paper, we assume the use of ContikiMAC, which is a popular asynchronous MAC protocol for 802.15.4 networks. Under this assumption, we propose an Intra-Layer Optimization for 802.15.4 Security (ILOS), which intertwines 802.15.4 security and ContikiMAC. In effect, ILOS reduces the security-related per-frame overhead even more than the LB optimization, as well as achieves strong freshness. Furthermore, unlike the LB optimization, ILOS neither incurs an increased RAM consumption nor requires resynchronization actions. Beyond that, ILOS integrates with and advances other security supplements to ContikiMAC. We implemented ILOS using OpenMotes and the Contiki operating system.
Secure Self-Seeding with Power-Up SRAM States.Krentz, Konrad-Felix; Meinel, Christoph; Graupner, Hendrik (2017).
Generating seeds on Internet of things (IoT) devices is challenging because these devices typically lack common entropy sources, such as user interaction or hard disks. A promising replacement is to use power-up static random-access memory (SRAM) states, which are partly random due to manufacturing deviations. Thus far, there, however, seems to be no method for extracting close-to-uniformly distributed seeds from power-up SRAM states in an information-theoretically secure and practical manner. Moreover, the min-entropy of power-up SRAM states reduces with temperature, thereby rendering this entropy source vulnerable to so-called freezing attacks. In this paper, we mainly make three contributions. First, we propose a new method for extracting uniformly distributed seeds from power-up SRAM states. Unlike current methods, ours is information-theoretically secure, practical, and freezing attack-resistant rolled into one. Second, we point out a trick that enables using power-up SRAM states not only for self-seeding at boot time, but also for reseeding at runtime. Third, we compare the energy consumption of seeding an IoT device either with radio noise or power-up SRAM states. While seeding with power-up SRAM states turned out to be more energy efficient, we argue for mixing both these entropy sources.
Countering Three Denial-of-Sleep Attacks on ContikiMAC.Krentz, Konrad-Felix; Meinel, Christoph; Graupner, Hendrik (2017).
Like virtually all media access control (MAC) protocols for 802.15.4 networks, also ContikiMAC is vulnerable to various denial-of-sleep attacks. The focus of this paper is on countering three specific denial-of-sleep attacks on ContikiMAC, namely ding-dong ditching, pulse-delay attacks, and collision attacks. Ding-dong ditching is when attackers emit interference, inject frames, or replay frames so as to mislead ContikiMAC into staying in receive mode for extended periods of time and hence consuming much energy. Pulse-delay attacks are actually attacks on time synchronization, but can also be launched against ContikiMAC’s phase-lock optimization to cause an increased energy consumption. Lastly, in collision attacks, an attacker provokes retransmissions via jamming. In this paper, to counter these three kinds of denial-of-sleep attacks, we propose two optimizations to ContikiMAC. The dozing optimization, on the one hand, significantly reduces the energy consumption under ding-dong ditching. Beyond that, the dozing optimization helps during normal operation as it reduces the energy consumption of true wake ups, too. The secure phase-lock optimization, on the other hand, is a version of ContikiMAC’s phase-lock optimization that resists pulse-delay attacks. Additionally, the secure phase-lock optimization makes ContikiMAC resilient to collision attacks, as well as more energy efficient. We implemented and evaluated both optimizations using the Contiki operating system and OpenMotes.
Demo: Enabling En-Route Filtering for End-to-End Encrypted CoAP Messages.Seitz, Klara; Serth, Sebastian; Krentz, Konrad-Felix; Meinel, Christoph (2017).
IoT devices usually are battery-powered and directly connected to the Internet. This makes them vulnerable to so-called path-based denial-of-service (PDoS) attacks. For example, in a PDoS attack an adversary sends multiple Constrained Application Protocol (CoAP) messages towards an IoT device, thereby causing each IoT device along the path to expend energy for forwarding this message. Current end-to-end security solutions, such as DTLS or IPsec, fail to prevent such attacks since they only filter out inauthentic CoAP messages at their destination. This demonstration shows an approach to allow en-route filtering where a trusted gateway has all necessary information to check the integrity, decrypt and, if necessary, drop a message before forwarding it to the constrained mote. Our approach preserves precious resources of IoT devices in the face of path-based denial-of-service attacks by remote attackers.
POTR: Practical On-the-fly Rejection of Injected and Replayed 802.15.4 Frames.Krentz, Konrad-Felix; Meinel, Christoph; Schnjakin, Maxim (2016).
The practice of rejecting injected and replayed 802.15.4 frames only after they were received leaves 802.15.4 nodes vulnerable to broadcast and droplet attacks. Basically, in broadcast and droplet attacks, an attacker injects or replays plenty of 802.15.4 frames. As a result, victim 802.15.4 nodes stay in receive mode for extended periods of time and expend their limited energy. He et al. considered embedding one-time passwords in the synchronization headers of 802.15.4 frames so as to avoid that 802.15.4 nodes detect injected and replayed 802.15.4 frames in the first place. However, He et al.’s, as well as similar proposals lack support for broadcast frames and depend on special hardware. In this paper, we propose Practical On-the-fly Rejection (POTR) to reject injected and replayed 802.15.4 frames early during receipt. Unlike previous proposals, POTR supports broadcast frames and can be implemented with many off-the-shelf 802.15.4 transceivers. In fact, we implemented POTR with CC2538 transceivers, as well as integrated POTR into the Contiki operating system. Furthermore, we demonstrate that, compared to using no defense, POTR reduces the time that 802.15.4 nodes stay in receive mode upon receiving an injected or replayed 802.15.4 frame by a factor of up to 16. Beyond that, POTR has a small processing and memory overhead, and incurs no communication overhead.
Handling Reboots and Mobility in 802.15.4 Security.Krentz, Konrad-Felix; Meinel, Christoph (2015).
To survive reboots, 802.15.4 security normally requires an 802.15.4 node to store both its anti-replay data and its frame counter in non-volatile memory. However, the only non-volatile memory on most 802.15.4 nodes is flash memory, which is energy consuming, slow, as well as prone to wear. Establishing session keys frees 802.15.4 nodes from storing anti-replay data and frame counters in non-volatile memory. For establishing pairwise session keys for use in 802.15.4 security in particular, Krentz et al. proposed the Adaptable Pairwise Key Establishment Scheme (APKES). Yet, APKES neither supports reboots nor mobile nodes. In this paper, we propose the Adaptive Key Establishment Scheme (AKES) to overcome these limitations of APKES. Above all, AKES makes 802.15.4 security survive reboots without storing data in non-volatile memory. Also, we implemented AKES for Contiki and demonstrate its memory and energy efficiency. Of independent interest, we resolve the issue that 802.15.4 security stops to work if a node's frame counter reaches its maximum value, as well as propose a technique for reducing the security-related per frame overhead.
6LoWPAN Security: Adding Compromise Resilience to the 802.15.4 Security Sublayer.Krentz, Konrad-Felix; Rafiee, Hosnieh; Meinel, Christoph (2013).
6LoWPAN is a protocol stack for seamlessly integrating 802.15.4-based wireless sensor networks with IPv6 networks. The security of 6LoWPAN widely depends on the 802.15.4 security sublayer. This sublayer also supports pairwise keys so as to mitigate node compromises. Currently, the establishment of pairwise keys is however unspecified. Moreover, broadcast keys are shared among multiple nodes, which is not compromise resilient. In this paper, we propose two energy-efficient and DoS-resilient 802.15.4 add-ons to fill these gaps: First, a pairwise key establishment scheme, which is adaptable to different 6LoWPAN networks and threat models. Second, an easy-to-implement and compromise-resilient protocol for authenticating broadcast frames. Together, our add-ons contain the effects of node compromises and provide a basis for detecting compromised nodes autonomously. We implemented both add-ons in Contiki and tested them on TelosB motes.