| |
|
Rotational cryptanalysis of ARX ciphers
Töpfer, Jakub ; Hojsík, Michal (advisor) ; Tůma, Jiří (referee)
We investigate functions which can be realized using only addition, XOR and rotation (ARX). Sometimes we admit operations with constants as well (ARX+C). We start our research from a theoretical point of view. We prove that every function can by written using only ARX+C operations and that we can even omit XOR. On the other hand, other combinations of these operations do not generate all functions. We also present an algorithm determining whether a function can be realised only by addition and XOR. After that we present a rotational cryptanalysis, which is designed especially for ARX ciphers. We demonstrate this method on reduced variants of Threefish, TEA and XTEA ciphers and discuss for which ciphers it is suitable. The last part of this thesis deals with a modification of rotational cryptanalysis called rotational rebound attack and shows its application on Threefish.
|
| |
| |
|
Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System
Čapek, David
Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System Abstract of the Ph.D. thesis \s David Capek It has been shown, that the thermal effects are very important in the dynamics of small Solar System bodies. A phenomenon which is known as the Yarkovsky effect is able to secularly change the semimajor axis of an orbit, while the YORP effect affects the rotation state of a body. The Yarkovsky effect and the YORP effect were previously calculated with many constraining assumptions like spherical shapes of asteroids, circular orbits, small variations of the surface temperature, principal axis rotation, constant thermal parameters, etc. We developed a sophisticated numerical model of the Yarkovsky/YORP effect without such simplifications. With this model, we have been able to describe the shape, the orbit, the rotation and the thermal behaviour of an asteroid in a very precise way. The YORP effect was studied on a sample of artificially generated shapes, roughly resembling Main Belt asteroids, and also on several shapes of real asteroids. The depen- dence of YORP on the obliquity and the thermal parameters of the surface were studied (Vokrouhlicky and Capek, 2002; Capek and Vokrouhlicky, 2004). A wide variety of pos- sible YORP evolution paths of the spin state was found. The possibility of...
|
|
Plánování cesty pro čtyřnohého kráčejícího robota použitím rychlých náhodných stromů
Krejsa, Jiří ; Věchet, S.
Summary: There are several randomized methods for problem of path planning. Rapidly exploring random trees (RRT) is a method which can deal with constraints typical for legged walking robots, e.g. limitations in rotation step resolution. Paper describes the RRT method itself and its use for path planning of four-legged walking robot, including special failure case when robot is capable of only rotating in one direction. The method proved to be robust and fast.
|
|
Mental rotation of simplex signs
Vobořil, Dalibor ; Šikl, Radovan
One of the basic cognitive operations which enables us to recognize observed objects is mental rotation. In order to recognize any object we are continuously encountering in our everyday life we rotate their image in our mind until it corresponds with a prototypical appearance of a given object stored in memory. It is evident that such operation takes longer time when the apparent differences between the image of actual and stored object is considerable, i.e. when it is viewed from rather different angle. Whether this time is dependent also on structural characteristics of mentally rotated object was the scope of present experiment. Subjects were asked to recognize stimuli of different shapes (letters R, G, F, J and Z) exposed in different orientations as measured by their deviation from usual position (from 0 degree to 180 degrees). Our results indicate that reaction time necessary to recognize differently shaped figures is interindividually variable but the profile of increment of reaction time with increasing angle is similar for all observers, no matter which of letters is observed.
|
|
Influence of rotating wheels on vehicle aerodynamic characteristics
Oslizlo, Aleš ; Svída, David (referee) ; Vančura, Jan (advisor)
The diploma thesis is focused on computational examination of influence of boundary condition settings in CFD software on the final aerodynamic characteristics of a vehicle. The flow analysis is carried out around a vehicle with and without the rotation of the wheels and along with the stationary and moving road. Furthermore, there is demonstrated the method of the CFD model composition and there is described the influence of rotating wheels on vehicle aerodynamic characteristics.
|
|
Studium expandujícího proudu termického plazmatu s využitím molekulových spekter
Mašláni, Alan ; Sember, Viktor
Thermal plasmas generated by plasma torches are well-known for their high temperatures and high enthalpies. Therefore optical emission spectroscopy is appropriate diagnostic method because of strong emission of radiation corresponding to the visible light. The decay of excited atoms, ions and molecules causes emission of the light at characteristic wavelengths. Except spectral lines of atoms and ions, also some molecular bands can be seen in the spectra of the plasma jet. Especially expanding thermal plasma jet operated under low pressure conditions offers possibility of observing molecular transitions. Pressure lower than atmospheric may cause the presence of supersonic flow and departures from thermodynamic equilibrium. Spectra of OH radical have been investigated using computer code LIFBASE, which contains a lot of data regarding spectra of diatomic molecules. Radial profiles of rotational and vibrational temperatures have been found in several regions of the jet.
|
| |
guest ::
