Publikationen

Modern FPGAs are equipped with the possibility of Partial Reconfiguration (PR) which along with other benefits can be used to enhance the security of cryptographic implementations. This feature requires development of alternative designs to be exchanged during run-time. In this work, we propose dynamically alterable circuits by exploring netlist randomization which can be utilized with PR as a countermeasure against physical attacks, in particular side-channel attacks. The proposed approach involves modification of an AES implementation at the netlist level in order to create circuit variants which are functionally identical but structurally different. In preliminary experiments, power traces of these variants have been shuffled to replicate the effect of partial reconfiguration. With these dynamic circuits, our experimental results show an increase in the resistance against power side-channel attacks by a factor of [Tilde] 12.6 on a Xilinx ZYNQ UltraScale+ device.

Communication metadata may leak sensitive information even when content is encrypted, e.g. when contacting medical services. Unfortunately, protecting metadata is challenging. Existing approaches for anonymous communications either are vulnerable in a strong (but feasible) threat model or have practicability issues like intense usage of asymmetric cryptography. We propose Hydra, a mix network that is able to provide multiple anonymous services in a uniform way. In contrast to previous messaging systems with strong anonymity, we deliberately use padded onion-encrypted circuits. This allows to support connectionless applications like contact discovery with authenticated key exchange, messaging, and dialing (signalling for connection-oriented communications) with strong anonymity and relatively low latency. Our cryptography benchmarks show that Hydra is able to process messages an order of magnitude faster than state of the art messaging systems with strong anonymity. At the same time, bandwidth overhead is comparable to previous systems. We further develop an analytical model to predict the end-to-end latency of Hydra and validate it in a testbed.

Second-order finite automata, introduced recently by Andrade de Melo and de Oliveira Oliveira, represent classes of languages. Since their semantics is defined by a synchronized rational relation, they can be studied using the theory of automatic structures. We exploit this connection to uniformly reprove and strengthen known and new results regarding closure and decidability properties concerning these automata. We then proceed to characterize their expressive power in terms of automatic classes of languages studied by Jain, Luo, and Stephan.

Non-volatile memory (NVM) offers lower costs per capacity and higher total capacities than DRAM. However, NVM cannot simply be used as a drop-in replacement for DRAM in database management systems due to its different performance characteristics. We thus investigate the placement of column-store data structures in a hybrid hierarchy of DRAM and NVM, with the goal of placing as much data as possible in NVM without compromising performance. After analyzing how different memory access patterns affect query runtimes when columns are placed in NVM, we propose a heuristic that leverages lightweight access counters to suggest which structures should be placed in DRAM and which in NVM. Our evaluation using TPC-H shows that more than 80% of the data touched by queries can be placed in NVM with almost no slowdown, while naively placing all data in NVM would increase runtime by 53%.

The field of optical lithography is subject to intense research and has gained enormous improvement. However, the effort necessary for creating structures at the size of 20 nm and below is considerable using conventional technologies. This effort and the resulting financial requirements can only be tackled by few global companies and thus a paradigm change for the semiconductor industry is conceivable: custom design and solutions for specific applications will dominate future development (Fritze in: Panning EM, Liddle JA (eds) Novel patterning technologies. International society for optics and photonics. SPIE, Bellingham, 2021. https://doi.org/10.1117/12.2593229). For this reason, new aspects arise for future lithography, which is why enormous effort has been directed to the development of alternative fabrication technologies. Yet, the technologies emerging from this process, which are promising for coping with the current resolution and accuracy challenges, are only demonstrated as a proof-of-concept on a lab scale of several square micrometers. Such scale is not adequate for the requirements of modern lithography; therefore, there is the need for new and alternative cross-scale solutions to further advance the possibilities of unconventional nanotechnologies. Similar challenges arise because of the technical progress in various other fields, realizing new and unique functionalities based on nanoscale effects, e.g., in nanophotonics, quantum computing, energy harvesting, and life sciences. Experimental platforms for basic research in the field of scale-spanning nanomeasuring and nanofabrication are necessary for these tasks, which are available at the Technische Universität Ilmenau in the form of nanopositioning and nanomeasuring (NPM) machines. With this equipment, the limits of technical structurability are explored for high-performance tip-based and laser-based processes for enabling real 3D nanofabrication with the highest precision in an adequate working range of several thousand cubic millimeters.