Collision Chains Research Articles

CoTree: A Side-Channel Collision Tool to Push the Limits of Conquerable Space

By introducing collision information into divide-and-conquer distinguishers, the existing collision-optimized side-channel attacks transform the given candidate space into a significantly smaller collision space, thus achieving more efficient key recovery. However, the candidates of the first several sub-keys shared by collision chains are still repeatedly detected, which happens very frequently and brings huge computational overhead. To alleviate this, we propose a highly-efficient collision-optimized attack named Collision Tree (CoTree). This collision detection tool exploits tree structure to store the chains created from the same sub-chain on the same branch, thus significantly reducing the storage requirements. It then benefits from the properties of both tree and collisions, and exploits a top-down tree building procedure and traverses each node only once when detecting their collisions with a candidate of the sub-key currently under consideration. Finally, unlike the traditional top-down node removal, CoTree launches a bottom-up branch removal procedure to remove the chains unsatisfying the collision conditions from the tree after traversing all the considered candidates of this sub-key, thus avoiding the traversal of the branches satisfying the collision condition. These strategies make our CoTree significantly alleviate the repetitive collision detection, and our experiments verify that it significantly outperforms the existing works.

A Monte Carlo code for the collisional evolution of porous aggregates (CPA)

Context. The collisional evolution of submillimeter-sized porous dust aggregates is important in many astrophysical fields. Aims. We have developed a Monte Carlo code to study the processes of collision between mass-asymmetric, spherical, micron-sized porous silica aggregates that belong to a dust population. Methods. The Collision of Porous Aggregates (CPA) code simulates collision chains in a population of dust aggregates that have different sizes, masses, and porosities. We start from an initial distribution of granular aggregate sizes and assume some collision velocity distribution. In particular, for this study we used a random size distribution and a Maxwell-Boltzmann velocity distribution. A set of successive random collisions between pairs of aggregates form a single collision chain. The mass ratio, filling factor, and impact velocity influence the outcome of the collision between two aggregates. We averaged hundreds of thousands of independent collision chains to obtain the final, average distributions of aggregates. Results. We generated and studied four final distributions (F), for size (n), radius (R), porosity, and mass-porosity distributions, for a relatively low number of collisions. In general, there is a profuse generation of monomers and small clusters, with a distribution F (R) ∝ R−6 for small aggregates. Collisional growth of a few very large clusters is also observed. Collisions lead to a significant compaction of the dust population, as expected. Conclusions. The CPA code models the collisional evolution of a dust population and incorporates some novel features, such as the inclusion of mass-asymmetric aggregates (covering a wide range of aggregate radii), inter-granular friction, and the influence of porosity.

Collision Chains among the Terrestrial Planets. III. Formation of the Moon

Abstract In the canonical model of Moon formation, a Mars-sized protoplanet “Theia” collides with proto-Earth at close to their mutual escape velocity v esc and a common impact angle ∼45°. The “graze-and-merge” collision strands a fraction of Theia’s mantle into orbit, while Earth accretes most of Theia and its momentum. Simulations show that this produces a hot, high angular momentum, silicate-dominated protolunar system, in substantial agreement with lunar geology, geochemistry, and dynamics. However, a Moon that derives mostly from Theia’s mantle, as angular momentum dictates, is challenged by the fact that O, Ti, Cr, radiogenic W, and other elements are indistinguishable in Earth and lunar rocks. Moreover, the model requires an improbably low initial velocity. Here we develop a scenario for Moon formation that begins with a somewhat faster collision, when proto-Theia impacts proto-Earth at ∼ 1.2v esc, also around ∼45°. Instead of merging, the bodies come into violent contact for a half hour and their major components escape, a “hit-and-run” collision. N-body evolutions show that the “runner” often returns ∼0.1–1 Myr later for a second giant impact, closer to v esc; this produces a postimpact disk of ∼2–3 lunar masses in smoothed particle hydrodynamics simulations, with angular momentum comparable to canonical scenarios. The disk ends up substantially inclined, in most cases, because the terminal collision is randomly oriented to the first. Moreover, proto-Earth contributions to the protolunar disk are enhanced by the compounded mixing and greater energy of a collision chain.

Collision Chains among the Terrestrial Planets. II. An Asymmetry between Earth and Venus

Abstract During the late stage of terrestrial planet formation, hit-and-run collisions are about as common as accretionary mergers, for expected velocities and angles of giant impacts. Average hit-and-runs leave two major remnants plus debris: the target and impactor, somewhat modified through erosion, escaping at lower relative velocity. Here we continue our study of the dynamical effects of such collisions. We compare the dynamical fates of intact runners that start from hit-and-runs with proto-Venus at 0.7 au and proto-Earth at 1.0 au. We follow the orbital evolutions of the runners, including the other terrestrial planets, Jupiter, and Saturn, in an N-body code. We find that the accretion of these runners can take ≳10 Myr (depending on the egress velocity of the first collision) and can involve successive collisions with the original target planet or with other planets. We treat successive collisions that the runner experiences using surrogate models from machine learning, as in previous work, and evolve subsequent hit-and-runs in a similar fashion. We identify asymmetries in the capture, loss, and interchange of runners in the growth of Venus and Earth. Hit-and-run is a more probable outcome at proto-Venus, being smaller and faster orbiting than proto-Earth. But Venus acts as a sink, eventually accreting most of its runners, assuming typical events, whereas proto-Earth loses about half, many of those continuing to Venus. This leads to a disparity in the style of late-stage accretion that could have led to significant differences in geology, composition, and satellite formation at Earth and Venus.

The unevenness of the north Iberian crustal root, a snapshot of an elusive stage in margin reactivation

AbstractCrustal roots are identified in collision chains worldwide. Frequently mirroring the summits of mountain systems, they elegantly encapsulate the concept of isostasy. The rugged topography of northern Iberia results from convergence with the European plate during the Alpine orogeny that formed the Pyrenean-Cantabrian mountain range. From east to west, the range comprises three distinct parts: the Pyrenees, the Basque Cantabrian region, and the Cantabrian Mountains. The identification of the Pyrenean root in the 1980s and the observation of a similar geometry beneath the Cantabrian range in the 1990s gave place to the current view of crustal thickening as a continuous feature, resulting from the northward subduction of Iberian crust. Recent developments in rift architecture have delivered a complex rifting template for the area prior to convergence, and contrasting views based on two-dimensional restorations have led to a debate over its evolution. A crucial geophysical constraint is Moho topography. Using two different data sets and techniques, we present the most accurate Moho surface to date, evidencing abrupt changes throughout the orogen. The complexity of hyperextended margins underlies the current Moho topography, and this is ultimately transferred to the nonuniform orogenic pattern found in northern Iberia.

Multiple-Differential Mechanism for Collision-Optimized Divide-and-Conquer Attacks

Several combined attacks have shown promising results in recovering cryptographic keys by introducing collision information into divide-and-conquer attacks to transform a part of the best key candidates within given thresholds into a much smaller collision space. However, these Collision-Optimized Divide-and-Conquer Attacks (CODCAs) uniformly demarcate the thresholds for all sub-keys, which is unreasonable. Moreover, the inadequate exploitation of collision information and backward fault tolerance mechanisms of CODCAs also lead to low attack efficiency. Finally, existing CODCAs mainly focus on improving collision detection algorithms but lack theoretical basis. We exploit Correlation-Enhanced Collision Attack (CECA) to optimize Template Attack (TA). To overcome the above-mentioned problems, we first introduce guessing theory into TA to enable the quick estimation of success probability and the corresponding complexity of key recovery. Next, a novel Multiple-Differential mechanism for CODCAs (MD-CODCA) is proposed. The first two differential mechanisms construct collision chains satisfying the given number of collisions from several sub-keys with the fewest candidates under a fixed probability provided by guessing theory, then exploit them to vote for the remaining sub-keys. This guarantees that the number of remaining chains is minimal, and makes MD-CODCA suitable for very high thresholds. Our third differential mechanism simply divides the key into several large non-overlapping “blocks” to further exploit intra-block collisions from the remaining candidates and properly ignore the inter-block collisions, thus facilitating the later key enumeration. The experimental results show that MD-CODCA significantly reduces the candidate space and lowers the complexity of collision detection, without considerably reducing the success probability of attacks.

Modeling and simulation of the IEEE 802.11e wireless protocol with hidden nodes using Colored Petri Nets

Wireless technologies are continuously evolving, including features such as the extension to mid- and long-range communications and the support of an increasing number of devices. However, longer ranges increase the probability of suffering from hidden terminal issues. In the particular case of Wireless Local Area Networks (WLANs), the use of Quality of Service (QoS) mechanisms introduced in IEEE 802.11e compromises scalability, exacerbates the hidden node problem, and creates congestion as the number of users and the variety of services in the network grow. In this context, this paper presents a configurable Colored Petri Net (CPN) model for the IEEE 802.11e protocol with the aim of analyzing the QoS support in mid- and long-range WLANs The CPN model covers the behavior of the protocol in the presence of hidden nodes to examine the performance of the RTS/CTS exchange in scenarios where the QoS differentiation may involve massive collision chains and high delays. Our CPN model sets the basis for further exploring the performance of the various mechanisms defined by the IEEE 802.11 standard. We then use this CPN model to provide a comprehensive study of the effectiveness of this protocol by using the simulation and monitoring capabilities of CPN Tools.

Network Traffic Sampling System Based on Storage Compression for Application Classification Detection

With the development of the Internet, numerous new applications have emerged, the features of which are constantly changing. It is necessary to perform application classification detection on the network traffic to monitor the changes in the applications. Using RelSamp to sample traffic can provide the sampled traffic with sufficient application features to support application classification. RelSamp separately assigns counters for each flow to record the statistical features and introduces a collision chain into the hash flow table to resolve hash conflicts in the table entries. However, in high-speed networks, owing to the number of concurrent flows and heavy-tailed nature of the traffic, the storage allocation method of RelSamp results in a significant waste of storage on the traffic sampling device. Moreover, the hash conflict resolution of RelSamp causes the collision chains of several hash table entries to be excessively deep, thereby reducing the search efficiency of the flow nodes. To overcome the shortcomings of RelSamp, this study presents a sampling model known as MiniSamp. Based on the RelSamp sampling mechanism, MiniSamp introduces shared counter trees to compress the storage space of the counters during the sampling process and integrates an efficient search tree into the hash table. The search tree structure is adjusted according to the network environment to improve the search efficiency of the flow nodes. The experimental results demonstrate that MiniSamp can effectively aid network operators to classify traffic in the high-speed network.

Collision chain mitigation and hidden device-aware grouping in large-scale IEEE 802.11ah networks

A new IEEE standard for large-scale wireless connectivity in IoT and M2M applications, called IEEE 802.11ah, has recently been introduced. A single access point (AP) of 802.11ah can provide connectivity to a large number of devices (up to 8192) with the communication range of up to 1 km. Due to such a large coverage area with a large number of connected devices, however, the hidden node problem of 802.11ah networks is severer than typical Wi-Fi networks. Especially, we observe that frequent occurrences of a collision chain results in significant deterioration of network performance even with the group-based access restriction mechanism of 802.11ah. To solve this problem, we propose a collision chain mitigation scheme that detects and interrupts a collision chain, lets a smaller number of devices contend thereafter and also provide the information from which a carrier-sensitivity table is constructed by AP. Although the proposed scheme mitigates performance deterioration due to a collision chain when occurred, collision chains still occur. So, we propose a grouping algorithm which can perform both initial grouping and regrouping from existing groups based on the carrier-sensitivity table constructed by the mitigation scheme so that only a negligible number of hidden devices remain in each group and the root cause of collision chain is obviated. Our simulation study shows that the mitigation scheme alone makes network throughput comparable to the case of no hidden devices and its combination with the grouping algorithm improves throughput performance over the 8-group case of the conventional mechanism by up to 146%.

Dynamical fluctuations in dense granular flows

We have made measurements of force and velocity fluctuations in a variety of dense, gravity-driven granular flows under flow conditions close to the threshold of jamming. The measurements reveal a microscopic state that evolves rapidly from entirely collisional to largely frictional, as the system is taken close to jamming. On coarse-grained time scales, some descriptors of the dynamics-such as the probability distribution of force fluctuations, or the mean friction angle-do not reflect this profound change in the micromechanics of the flow. Other quantities, such as the frequency spectrum of force fluctuations, change significantly, developing low-frequency structure in the fluctuations as jamming is approached. We also show evidence of spatial structure, with force fluctuations being organized into local collision chains. These local structures propagate rapidly in the flow, with consequences far away from their origin, leading to long-range correlations in velocity fluctuations.

Effect of various components of slightly diluted tungsten-based alloys on the formation of defects in atomic displacement cascade regions: Field-ion microscopic analysis

New complex field-ion microscopic data for the formation of radiation-induced defects in VChV ultrapure tungsten, VA-3 commercial-grade tungsten, and four slightly diluted tungsten-based alloys (W-Hf-C, P39A; W-1.5% ThO2, VT-15; W-5% Re, VR-5; and W-2% Fe, VZh-2) are reported. Samples were irradiated in an external unit by Ar+ and Ni+ ions of energy 35 keV. In the experiments, the ion current is kept at j=2.0 µA and the irradiation fluence equals Φt=5×1014 ions/cm2. The clustering of single vacancies in samples irradiated is studied in relation to the impurity concentration and type. The distribution of vacancy clusters over the number of aggregated single vacancies is studied. These distributions are found to differ noticeably inside and outside the depletion zones. The mean lengths of focused substitutional atomic collision chains in samples with different impurity concentrations and types are measured indirectly. From these data, the efficiency of trapping intrinsic interstitials by various impurities in tungsten is estimated.

Displacement threshold energies in high-temperature superconductors

The running of CuO collision chains in the (001) direction is investigated in YBA 2Cu 3O 7 by the molecular dynamics method. We show that there are two ways of point defect formation in these chains. The first one creates a stable Frenkel pair in the Cu sublattice. The second process is the displacement of an oxygen ion from the position in the chain to an O(5) vacancy. The angular dependences of the second displacement threshold energy are presented. The influence of an injection of additional oxygen has been investigated. The contour of the threshold energy can be drastically changed by introducing oxygen in vacant sites.

Computer simulations on sputtering mechanisms: Bombardment of single-crystalline Cu(100) by Ar ions.

The sputtering mechanisms of monocrystalline Cu are studied using the binary-collision lattice-simulation code cosipo. Single-crystal Cu (100) is irradiated with normally incident 5-keV Ar ions. The backward-directed modified recoil flux is compared to the angular distribution of sputtered particles in order to follow the sputtering process. The angular distribution of sputtered particles is directly related to the modified recoil flux and collision cascade anisotropies. Particular attention is given to different mechanisms acting in single-crystalline sputtering. Both the collision sequence and Lehmann-Sigmund mechanisms are found to take place. The collision chains are mainly of the short-range type, except for the 〈110〉 replacement and directional ones. The 〈110〉 and 〈100〉 sequences dominate the angular distribution of sputtered particles. The contribution of defocused sequences is higher than that of replacement and focused ones. The sputtering yield and angular distribution of sputtered particles are evaluated as a function of target thickness. Fifteen atomic layers are sufficient to achieve the bulk yield and spot pattern of sputtered particles that corresponds well to that of a monocrystalline target. The Lehmann-Sigmund model is simulated by employing a target with a varying number of (100) atomic layers on the top of the amorphous bulk. Calculations show that two atomic layers of regular structure on the top of the amorphous bulk reproduces the main features of the spot pattern of sputtered atoms, but is inadequate in explaining the collision sequence mechanisms of monocrystalline sputtering.

The dynamic crowdions and point defect formation in high temperature superconductors

The running of CuO collision chains in the (001) direction is investigated in YBa 2Cu 3O 7 by the molecular dynamics method. The pair potential which contained the members responsible for Coulomb and repulsive interaction was used for the description of the interactions between the ions. Appreciable fluctuations of oxygen ions reminding of thermal ones were observed. An energy transmission process through a chain quickly subsided. The origination of the colision chain may be observed in the direction opposite to the initial direction of the motion of the primary knock atom (an oxygen ion). The threshold energy values E d were found for a given chain with different initial direction of motion and types of primary knock atom. The atomic configurations of the interstitial copper and copper vacancy were determined as well as V O + V Cu, I O + I Cu.

External stress effects on radiation damage dynamics

Abstract External uniaxial stress effects on the radiation damage dynamics in a a-Fe b.c.c. structure are studied by means of the computer simulation method. Focused collision chains, defocused ones, and atom-atom collision cascades were simulated. The external uniaxial stresses affect the intervals between a vacancy and an interstitial atom produced due to a collision chain, i.e. changes a dynamical crowdion path. The external stresses change the number of stable point defects and their arrangement in the cascade development region if an atom-atom collision cascade develops in a stressed crystal. The studies of focused collision chains of energies close to the atom displacement threshold energies show that the latter can either increase or decrease due to the external stresses depending on the direction of the effect.

Caging of an interstitial impurity in the vicinity of a collision cascade

Abstract A computer experiment has been carried out, using the dynamics simulation method, to simulate impurity migration by local ‘heating-like’ collision cascades and to study the simplest mechanisms of their displacements, in particular caging. Two types of interstitial impurity, Ag in Au and He in α-Fe, are chosen as witness defects. The primary knock-on atom, with an energy up to 500 eV, produces the collision cascades. The witness impurities are placed at different locations outside the cascade development area in such a way that they do not fall under the direct influence of the replacement collision chains of which the cascades are composed. It has been found that the interstitial witness impurities make single and multiple jumps under the influence of the developing cascades. The nature of the jumps is different. In most cases the Ag impurity atoms were found to jump in the Au matrix by an interchange of the atoms in a mixed dumb-bell within a basic cell of Au.

Computer simulation of single-crystal and polycrystal sputtering—III

Abstract This part of the work completes the discussion of the results of computer simulation of Cu single-crystal and polycrystal sputtering by 27-keV Ar ions. Sputtering due to <110> linear collision chains is investigated here in detail. The effects of thermal vibrations and simultaneous collisions (lens focusing) on the parameters of the <110> collision chains are discussed. The energy spectra of atoms sputtered by the <110> collision chains of various types and the data concerning the initial formation stage of the <110> collision chains are presented. The characteristic energies in the spectra of atoms sputtered by pure focused and mixed (focused-defocused) collision chains have been shown to be different. Collision chains along an isolated Cu <110> atomic row are calculated as a subsidiary problem. The ranges of initial angles and energies pertaining to various types of collision chains have been found. The hard-sphere approximation and the many-body integration method were also used in some of the calculations for the sake of comparison. The angular dependence of the single-crystal sputtering yield studied in Part 1 of the work is discussed again in the light of new experimental data.

Computer simulation of single-crystal and polycrystal sputtering. II

Abstract Examination of the results of computer simulation of Cu single-crystal and polycrystal sputtering by 27 keV Ar ions started in Part I of the present work is continued. The spatial and energy distributions of all sputtered atoms and various sputtering components are analysed here. The incidence angles α = 45° and 85° are taken as examples. The sputtering is shown to be mainly near the <110> and <100> axes and also, especially in the case of glancing incidence, near a plane perpendicular to the ion beam. The mechanisms of predominant sputtering are discussed in detail. The importance of linear collision chains and correlated collisions of the incident ions with the atomic rows of a crystal lattice is emphasized. It is noted that bombardment of a crystal under semichannelling conditions is favourable for the target to be sputtered in the form of clusters. In connection with Harrison's recent remarks on Sigmund's sputtering theory, the relationship of the energy of sputtered atoms to the depth of their production in a crystal is examined. The mean depth from which the sputtered atoms are ejected has been found to be a nonmonotonic function of their energy.

Computer simulation of single-crystal and polycrystal sputtering I

Abstract Sputtering of Cu single-crystal and polycrystal targets by 27 keV Ar ions has been simulated using the new binary collision cascade computer program OKSANA. The sputtering yield, the sputtering and reflection efficiencies, and the absolute and relative contributions to sputtering from various components have been calculated in a broad range of incidence angles. The obtained angular dependences of the sputtering yield have proved to agree with experimental data. Some features of sputtering due to semichannel focusing of incident particles have been found. The contributions to sputtering from several types of linear collision chains and from the primary knock-on atoms are considered in most detail. It has been shown, in particular, that the pure focused, pure defocused, and mixed focused-defocused collision chains contribute noticeably to sputtering. The contribution from the primary knock-on atoms is angle-dependent and reaches its maximum in the range of glancing angles for both single-crystal an...

Anisotropy of the displacement energy in single crystals of molybdenum

Abstract A “geometrical” model for the threshold cnergy surfaceof a b.c.c. lattice is applied to analyse recent measurements of the resistivity change rates in electron-irradiated monocrystalline molybdenum specimens with the orientations [100], [11O], [111] and [112]. Cross sections computed with this surface were matched to the experimental data using various sets of threshold energies as parameters. The best fit was obtained with Td [100] = (35+2 −2) eV, Td [1101 > 2Td [100], Td [111] = (45 f 3) eV. When corn ared to the experimental damage rates the absolute values for the cross sections yield a Frenkel pair resistivity pio = (13 f 2) pfl cm/at.% F.P. Expressions for the energy necessary to penetrate the potential barriers in the principal crystallographic directions are derived and compared to the id[iik] obtained before, with the interatomic potential as parameter. Taking into account the length of the [111] collision chains and the size of the spontaneous recombination volume, the appropriate potential can be chosen in the range between UMo(r)/eV = 3000 exp(−3.2 r/A) and 11,000 exp(−3.8 r/A). An analysis of the displacement cross sections permitted to explain the energy and orientation dependence of stage I recovery and to attribute the sub-stages a t 15 K and 40 K to the annealing o f interstitials due to [100] displacements and the substages between 20 and 33 K to that of [111] chains of various lengths.