On security arguments of the second round SHA-3 candidates

In 2007, the US National Institute for Standards and Technology (NIST) announced a call for the design of a new cryptographic hash algorithm in response to vulnerabilities like differential attacks identified in existing hash functions, such as MD5 and SHA-1. NIST received many submissions, 51 of which got accepted to the first round. 14 candidates were left in the second round, out of which five candidates have been recently chosen for the final round. An important criterion in the selection process is the SHA-3 hash function security. We identify two important classes of security arguments for the new designs: (1) the possible reductions of the hash function security to the security of its underlying building blocks and (2) arguments against differential attack on building blocks. In this paper, we compare the state of the art provable security reductions for the second round candidates and review arguments and bounds against classes of differential attacks. We discuss all the SHA-3 candidates at a high functional level, analyze, and summarize the security reduction results and bounds against differential attacks. Additionally, we generalize the well-known proof of collision resistance preservation, such that all SHA-3 candidates with a suffix-free padding are covered.     

Etablierung einer nationalen Rohstoffbuchhaltung und dafür notwendige Informationen und Informationsgüte

The influence of anthropogenic processes on global material flow systems increasingly dominates the influence of natural processes. In this context, the provision of detailed knowledge on material flow systems is relevant for decision makers in resource policy. This information can be provided in the form of one-year material balances or, if repeated over a period of consecutive years, in the form of national resource budgets. In national resource budgets, all relevant flows of a material through a national economy are balanced and displayed in neatly arranged diagrams. By updating these material balances over a series of years, the development of material stocks can be estimated. Upcoming challenges both regarding supply and disposal of materials can be identified. Comprehensive balances are useful for decision makers in resource policy and, moreover, as an information basis for future exploitation of anthropogenic resources. However, both availability of data and possibilities for assessing the reliability of data are very limited. In this work, a methodology for investigating and evaluating the information basis of national resource budgets is presented. The methodology includes procedures for systematic characterization of resource budget data and formal procedures for evaluating their reliability. From a scientific perspective, the methodology contributes to understanding material flow systems better. It also enables implementing procedures towards national resource budgets in an administrative context.     

Anteil erneuerbarer Energien und klimarelevante CO2-Emissionen aus der thermischen Verwertung von Abfällen in Österreich

Since combustible wastes usually consist of biogenic (e.g. paper, wood, food waste) and fossil organic matter (plastics), their thermal recovery results in climate neutral and climate relevant CO₂ emissions. Moreover, the fraction of biogenic materials in the waste feed is relevant for the amount of renewable energy produced. The latter has to be reported and might be subsidized according to national laws (e.g. based on European directive 2009/28/EG). The present study represents the first comprehensive evaluation of the share of biogenic and fossil materials in the waste feed of waste-to-energy (WTE) plants on a national basis. The Balance Method, which is patented on a European level by TU Wien, was applied to 10 out of 13 Austrian WTE plants (around 2.3 Mio tons of waste corresponding to around 88 % of the overall waste feed in Austrian WTE plants). The method is based on the mathematical reconciliation of the material properties (e.g. mean chemical composition of biogenic and fossil materials) and routinely recorded operating data of WTE plants (e.g. flue gas volume, CO₂ and O₂-content in the dry flue gas, steam production). The results demonstrate large variations for the share of energy from biogenic sources in the different WTE plants, ranging from 35.7 ± 2.4 % to 61.2 ± 2.7 % (based on annual averages). Additionally, for several WTE plants large temporal variations can be observed based on monthly mean values. Thus, a plant-specific and continuous evaluation of the waste composition in WTE plants (which the Balance Method allows to do at reasonable efforts) can be recommended for a reliable reporting of the renewable share of energy or fossil CO₂ emissions from waste incineration. The energy input which stems from fossil and biogenic sources can be estimated to 11,450 ± 120 TJ and 10,730 ± 110 TJ, respectively for the year 2014 (for the 10 WTE plants). In total 1060 ± 24 kt fossil CO₂ emissions from the thermal recovery of waste in Austria’s WTE plants in 2014 could be determined (estimation for all 13 WTE plants).     

A new method to determine the ratio of electricity production from fossil and biogenic sources in waste-to-Energy plants

New directives of the European Union require operators of waste-to-energy (WTE) plants to report the amount of electricity that is produced from renewable sources in the waste feed. Until now, the standard method to determine the portion of renewable electricity is sorting the wastes into defined fractions of fossil organic and biogenic waste components and determining the lower heating value of these fractions. Out of it the amount of electricity production from renewables is calculated. This practice is labor and cost intensive. Therefore, it is usually carried out once a year which provides only a snapshot analysis of limited significance. This paper proposes a method to calculate the portion of electricity produced from renewable materials in waste continuously by solving a set of equations. All data required are either available from literature or from operating data routinely measured in WTE plants. The advantages are statistically derived uncertainty of the result, temporal resolution of the result down to daily mean values, low implementation efforts, and virtually no operational costs. An example of the implementation of the method to a 60 000 tons per year WTE plant is given.     

Throughput Analysis of a Decentralized RLAN Based on Asynchronous DS/CDMA Using Random Periodic Spreading Sequences

Packet throughput figures are obtained for a decentralized radio local area network (RLAN) which is based on asynchronous direct-sequence code-division multiple-access (DS/CDMA). Packets arrive at the receiver nodes with different power levels. Techniques are developed to derive the probability of packet success for a system employing random periodic spreading sequences. It can be shown, that this system performs far better than a network using random spreading sequences. Based on the packet error probability, throughput figures of slotted DS/CDMA-ALOHA are presented for various scenarios. The effect of applying forward error correction (FEC) is investigated. For finite user environments, additional sources of errors have to be considered. These have a major impact and reduce the overall system performance. Finally, the throughput figures of a system applying the binary exponential backoff algorithm to avoid unstable behavior is investigated. The performance figures of the various systems described in this paper show that DS/CDMA forms a valuable choice for future RLANs.     

Nonaqueous sol‐gel synthesis of InTaO4 nanoparticles and their assembly into macroscopic aerogels

Due to their band gap energy, metal tantalates absorb both ultraviolet and visible parts of the solar spectrum, which is beneficial to applications in photocatalysis. However, tantalates are very challenging to synthesize. In comparison to traditional solid‐state reactions, which often lead to impurities, wet‐chemical approaches starting from molecular precursors offer better homogeneity. In this study, amorphous InTaO₄ nanoparticles were synthesised in a nonaqueous sol‐gel method. Subsequent annealing at 800°C yielded crystalline and phase‐pure nanoparticles. In addition, the amorphous nanoparticles could be used as building blocks for the assembly into macroscopic gels by careful centrifugation. After supercritical drying, the three‐dimensionally interconnected microstructure was preserved, resulting in highly porous aerogel monoliths with a large surface area of 357 m² g^?1. Upon calcination, crystallization and 46% shrinkage of the aerogel occurred and a decrease in surface area to 49 m² g^?1 was observed. Uniaxial compression tests revealed the mechanical stability of these nanoparticle‐based aerogels. Although the large surface area and the ability to absorb visible light, combined with the unique mechanical properties, are ideal prerequisites to make these aerogels promising for photocatalytic reactions, the degradation of methylene blue only showed limited success.     

A method for determining buildings’ material composition prior to demolition

A prerequisite of the efficient recycling of demolition waste and its evaluation in terms of the material specific recycling rates is information on the composition of the building material stock (as the source of future demolition waste). A practical method is presented that characterizes the material composition of buildings prior to their demolition. The characterization method is based on the analysis of available construction documents and different approaches of on-site investigation. The method is tested in different buildings and the results from four case studies indicate that the documents are useful to quantify bulk materials (e.g. bricks, concrete, sand/gravel, iron/steel and timber). However, on-site investigations are necessary to locate and determine the trace materials such as metals (e.g. copper and aluminium), or different types of plastics. The overall material intensity of the investigated buildings ranges from 270 to 470?kg/m³ gross volume. With ongoing surveys about the composition of different buildings, the collected data will be used to establish a building-specific database about the amount of materials contained in Vienna's building stock.