Martin Novotny

Uncertainty Analysis of the RMS Value and Phase in the Frequency Domain by Noncoherent Sampling

The determination of RMS value and phase of harmonic components belongs to the most important tasks of signal analysis in the frequency domain. Evaluation of these parameters is frequently performed using a discrete Fourier transform (DFT) algorithm. In practice, signals are mostly sampled noncoherently. This leads to the well-known effect called leakage, i.e., spreading energy of signal harmonic components into signal frequency neighboring frequency bins. Signals are multiplied by tapering time windows for leakage suppression. This paper is focused on the uncertainty analysis of the RMS value and phase computed from the DFT spectrum of the noncoherently sampled signal using cosine windows. The analysis is focused on investigating the influence of quantization noise

Breaking Hitag2 with Reconfigurable Hardware

The Hitag2 stream cipher is used in many real world applications, such as car immobilizers and door opening systems, as well as for the access control of buildings. The short length of the 48-bit secret key employed makes the cipher vulnerable to a brute-force attack, i.e., exhaustive key search. In this paper we develop the first hardware architecture for the cryptanalysis of Hitag2 by means of exhaustive key search. Our implementation on the Cost-Optimized Parallel Code-Breaker COPACOBANA is able to reveal the secret key of a Hitag2 transponder in less than 2 hours (103.5 minutes) in the worst case. The speed of our approach outperforms all previously proposed attacks and requires only 2 sniffed communications between a car and a tag. Our findings thus define a new lower limit for the cloning of car keys in practice. Moreover, the attack is arbitrarily parallelizable and could thus be run on multiple COPACOBANAs to decrease the time to find the secret key.

The influence of window sidelobes on DFT-based multifrequency signal measurement

One of the causes influencing the uncertainty of the measured parameter is the mutual influence of the window spectra contained in the multifrequency signal spectrum. This paper analyses the effect of window spectrum sidelobes on the evaluation of multifrequency signal RMS value estimated by two DFT-based techniques (the mainlobe method and RMS value estimation using interpolated DFT). The RMS bias caused by window sidelobes when applying twelve different generalized cosine windows is compared. Both simulation results and theoretical relations are included. The presented principle is applicable for all DFT based algorithms, not only for those used for RMS value estimation.

The evaluation of the refractive indices of bulk and thick polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers by the prism coupling technique

This paper presents the study of the optical properties of bulk and thin-film samples made from polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers. The chemical structures of the prepared elastomer samples were characterised by infrared spectroscopy. Also their transmission spectra were measured in the visible and infrared regions. The refractive indices of the samples were measured by the prism coupling technique using dark mode spectroscopy for five wavelengths (473, 632.8, 964, 1311 and 1552xa0nm). Particular focus was placed on the effect of the dependence of refractive index on the conditions of deposition. It has been found that the changes of refractive indices can be achieved by the modification of deposition conditions (hardening temperature and/or A:B mixedxa0agent ratios). In order to obtain more significant changes of the refractive indices, we recommend using polydimethyl-diphenylsiloxane elastomer as a waveguide layer because of it content of phenyl groups, which lead to an increase in the value of the refractive index.

Education of Digital and Analog Circuits supported by computer algebra system

We describe our approach in education of the course Digital and Analog Circuits, which belongs to curricula of the Informatics study program. For analysis of analog and simple digital circuits we use computer algebra system Mathematica, which minimizes the amount of routine, handy calculations. This fact enables focusing on the problem and solving more examples, which in turn provides better comprehension of the topic. As Mathematica is later used in subsequent courses, its knowledge is utilized in these courses. Last, but not least, Mathematica provides several programming paradigms, which can be easy demonstrated to students of Informatics study program.

A DSP Based Prototype for Water Conductivity Measurements

In this paper a four-electrode measurement cell is proposed for conductivity measurements. The main advantages of these cells include a wide measurement range and an intrinsic capability to minimize errors caused by fouling and polarization effects. The implemented prototype provides a flexible solution for data acquisition and signals processing and includes a capability to generate excitation signals of different frequencies and amplitudes. The proposed measurement method uses data from both, voltage and current channels to estimate the sine amplitudes, phases, DC components and common frequency, reducing the uncertainty of the estimated parameters. Conductivity temperature dependence is compensated by using a temperature sensing unit

Lightweight cipher resistivity against brute-force attack: Analysis of PRESENT

The PRESENT cipher is symmetric block cipher with 64 bits of data block and 80 (or 128) bits of key. It is based on Substitution-permutation network and consists of 31 rounds. PRESENT is intended to be implemented in small embedded and contactless systems, thus its design needs only small amount of chip area and consumes low power. In this work we evaluate the resistance of PRESENT against brute-force attack. We determine the computational demand of this type of attack conducted on special parallel hardware COPACOBANA consisting of array of FPGA chips with custom design.

Differential Power Analysis under Constrained Budget: Low Cost Education of Hackers

The differential power analysis is popular technique in exploiting weaknesses of the embedded systems - mostly of the smart cards. This approach is understandable as the DPA does not require expensive equipment or strong theoretical background on the device under attack. Therefore it is ideal for education of beginners or students in the field of computer security. The aim of this paper is to describe the economy of obtaining the basic equipment for the education of the differential power analysis and to share the experience with its teaching.

Two Architectures of a General Digit-Serial Normal Basis Multiplier

We present two architectures of digit-serial normal basis multiplier over GF(2m). Proposed multipliers are scalable by the digit width of general value in difference of the multiplier of Agnew et al., that may be scaled only by digit width that divides the degree m. This helps designers to trade area for speed e.g. in cryptographic systems, where m should be a prime number. Functionality of multipliers has been tested by simulation and implemented in Xilinx Virtex 4 FPGA

Cryptanalytical attacks on cyber-physical systems

Cryptography finds its application area in many contemporary object of daily usage. GSM communication, credit cards, tickets for public transport or RFID tags employ cryptographic features either to protect privacy or to ensure trustworthy authentication. However, many such objects are vulnerable to certain cryptanalytical attacks. In our presentation we will discuss how FPGA-based cryptanalytical hardware may compromise GSM communication, or how standard laboratory equipment may be used for breaking SmartCard security. Finally, we would debate one of recent cryptographic challenges, namely protection of dependable systems against cryptanalytical attacks.