Sven Frohmann

Physical Characterization of Arbiter PUFs

As intended by its name, Physically Unclonable Functions PUFs are considered as an ultimate solution to deal with insecure storage, hardware counterfeiting, and many other security problems. However, many different successful attacks have already revealed vulnerabilities of certain digital intrinsic PUFs. Although settling-state-based PUFs, such as SRAM PUFs, can be physically cloned by semi-invasive and fully-invasive attacks, successful attacks on timing-based PUFs were so far limited to modeling attacks. Such modeling requires a large subset of challenge-response-pairs CRP to successfully model the targeted PUF. In order to provide a final security answer, this paper proves that all arbiter-based i.e. controlled and XOR-enhanced PUFs can be completely and linearly characterized by means of photonic emission analysis. Our experimental setup is capable of measuring every PUF-internal delay with a resolution of 6 picoseconds. Due to this resolution we indeed require only the theoretical minimum number of linear independent equations i.e. physical measurements to directly solve the underlying inhomogeneous linear system. Moreover, we neither require to know the actual PUF challenges nor the corresponding PUF responses for our physical delay extraction. On top of that devastating result, we are also able to further simplify our setup for easier physical measurement handling. We present our practical results for a real arbiter PUF implementation on a Complex Programmable Logic Device CPLD from Altera manufactured in a 180 nanometer process.

Modeling of multilayer microholographic data storage

We focus on the investigation of multilayer recording in microholographic data storage. We have developed a numerical model for calculating the electromagnetic scattering from thick microholographic gratings using the Born approximation and the direct volume integral. The signal-to-noise ratio and bit error rate were calculated to estimate the noise arising from interlayer and interhologram cross talk. Measurements were done to prove the validity of the model. The results of our calculations and the measurements show good agreement. We present the application of the model to the investigation of confocal filtering at the image plane and to the evaluation of positioning and wavelength tolerances.

Optical investigation of photopolymer systems for microholographic storage

We investigate different classes of organic photosensitive materials in order to optimize the interaction between the material itself and a surrounding optoelectronic system. The focus of investigation is the application to microholographic data storage. Key issues are the dynamic material response, spatial resolution and photoresponse, spectral and temporal grating development, influence of the light intensity distribution, and impact of pre-exposure. The materials under investigation are cationic ring opening and free radical polymerization systems.

Modeling material saturation effects in microholographic recording

Microholographic data storage system model is presented that includes non-linear and non-local behavior of the storage material for accurate simulation of the system and optimization of the writing process. For the description of the photopolymer material a diffusion based nonlocal material model is used. The diffusion equation is solved numerically and the modulation of the dielectric constant is calculated. Diffraction efficiency of simulated microholograms and measurements were compared, and they show good agreement.

High-density multilayer recording of microgratings for optical data storage

A novel approach to 3D optical information storage based on writing and reading of microscopic holographic gratings in a photopolymer layer is presented. Strongly localized reflection gratings created by two highly focused laser beams are used to replace the pit and land structure of the CD/DVD technology. The holographic recording method presented here allows employing various multiplexing methods. A combination of wavelength multiplexing and multilayer storage is proposed to achieve storage densities similar to page-oriented holographic data storage. In this paper we report on recording and readout of submicron-sized gratings using diffraction limited laser beams. The transversal extent of a micrograting corresponds to the optical resolution limit. Track spacing and bit-to-bit separation are about 500 nm. The interlayer spacing through the depth of the photopolymer is less than 8 micron. This way a 3D structure is realized that even refines the surface data structure of current DVDs.

Resolution-limited optical recording in 3D

We present an optical write/read system for high density optical data storage in 3-D. The microholographic approach relies on submicron-sized reflection gratings that encode the digital data. As in conventional optical data storage, the physical limitations are imposed by both the diffraction of light and resolution of the recording material. We demonstrate resolution-limited volume recording in photopolymer materials sensitive in the green and violet spectral range. The volume occupied by a micrograting scales down by the transition in the write/read wavelength. Readout yields a micrograting width of 306 nm at 532 nm and 197 nm at 405 nm. To our knowledge these are the smallest volume holograms ever recorded. The recordings demonstrate the potential of the technique for volumetric optical structuring, data storage and encryption.

Multilayer recording in microholographic data storage

The potential of multilayer recording in microholographic data storage is investigated. Micrometer-scaled depth localization of resolution-limited microgratings is achieved in photopolymers sensitized to green and violet light. Confocal readout results in an optical depth of approximately 2 μm. The spatial Bragg selectivity of resolution-limited micrograting structures allows reducing their longitudinal depth spacing down to 4 μm. Multilayer recording is demonstrated as depth multiplexing of microgratings written in 50 layer locations within a 300 μm thick photopolymer.

Volumetric optical storage with microholograms

Research activities and development paths toward a fully functional optical drive system based on the microholographic storage approach are presented. Our write/read system relies on a simple optical configuration where a single diffraction limited beam is used to generate subwavelength sized reflection holograms. Setups for microlocalized write/read operation and a media tester for flexible characterization of different recording materials are developed. Recent progress in dynamic multilayer recording of resolution limited microholographic lines is reported. We discuss the target specification and related conception of a microholographic storage system. Advanced system solutions allow for compensating the spherical aberration and limited diode laser coherence in a compact microholographic drive.

Photonic Side-Channel Analysis of Arbiter PUFs

As intended by its name, physically unclonable functions (PUFs) are considered as an ultimate solution to deal with insecure storage, hardware counterfeiting, and many other security problems. However, many different successful attacks have already revealed vulnerabilities of certain digital intrinsic PUFs. This paper demonstrates that legacy arbiter PUF and its popular extended versions (i.e., feed-forward and XOR-enhanced) can be completely and linearly characterized by means of photonic emission analysis. Our experimental setup is capable of measuring every PUF internal delay with a resolution of 6 ps. Due to this resolution, we indeed require only the theoretical minimum number of linear independent equations (i.e., physical measurements) to directly solve the underlying inhomogeneous linear system. Moreover, it is not required to know the actual PUF responses for our physical delay extraction. We present our practical results for an arbiter PUF implementation on a complex programmable logic device manufactured with a 180 nm process. Finally, we give an insight into photonic emission analysis of arbiter PUF on smaller chip architectures by performing experiments on a field programmable gate array manufactured with a 60 nm process.

Highly resolved spatial and temporal photoemission analysis of integrated circuits

We develop an optical system for highly resolved photoemission analysis of integrated circuits. Photons emitted by switching transistors allow the operation of an integrated circuit to be observed by recording the individual photoemission acts. The ongoing feature size reduction makes the space–time-resolved detection of these extremely weak photoemissions challenging. We combine different optical and photonic solutions to achieve both a high spatial and temporal resolution in a compact analysis system. Imaging and detection modules capture photons through the substrate during normal chip operation and perform highly resolved optical analysis. We demonstrate the system capability by photoemission records of a real-world IC device.