On improving resistance to Denial of Service and key provisioning scalability of the DTLS handshake

DTLS is a transport layer security protocol designed to provide secure communication over unreliable datagram protocols. Before starting to communicate, a DTLS client and server perform a specific handshake in order to establish a secure session and agree on a common security context. However, the DTLS handshake is affected by two relevant issues. First, the DTLS server is vulnerable to a specific Denial of Service (DoS) attack aimed at forcing the establishment of several half-open sessions. This may exhaust memory and network resources on the server, so making it less responsive or even unavailable to legitimate clients. Second, although it is one of the most efficient key provisioning approaches adopted in DTLS, the pre-shared key provisioning mode does not scale well with the number of clients, it may result in scalability issues on the server side, and it complicates key re-provisioning in dynamic scenarios. This paper presents a single and efficient security architecture which addresses both issues, by substantially limiting the impact of DoS, and reducing the number of keys stored on the server side to one unit only. Our approach does not break the existing standard and does not require any additional message exchange between DTLS client and server. Our experimental results show that our approach requires a shorter amount of time to complete a handshake execution and consistently reduces the time a DTLS server is exposed to a DoS instance. We also show that it considerably improves a DTLS server in terms of service availability and robustness against DoS attack.     

Performance evaluation of semantic registries: OWLJessKB and instanceStore

Service discovery is a critical task in distributed computing architectures for finding a particular service instance. Semantic annotations of services help to enrich the service discovery process. Semantic registries are an important component for the discovery of services and they allow for semantic interoperability through ontology-based query formulation and dynamic mapping of terminologies between system domains. This paper evaluates two semantic registries—OWLJessKB implementation and instanceStore—to determine the suitability of these with regards to the query response time and the overall scalability for use in mathematical services. Mathematical ontologies from the MONET project are used to undertake comparison. The results demonstrate that the performance of registries may be compared across two axes: (1) time to initialize (i.e. time to load an initial ontology into memory); (2) time to query (i.e. time to reason with an ontology loaded into memory).     

Application of polymerase chain reaction for the correlation of Salmonella serovars recovered from greyhound feces with their diet

The polymerase chain reaction was employed to correlate Salmonella serovars isolated from fecal material of greyhounds suffering from gastroenteritis with those isolated from the diet fed to the greyhounds prior to onset of diarrhea. Kennels around the Abilene, Kansas, area were contacted and supplied with materials needed to collect a portion of the diet each day. With the onset of diarrhea, the kennels were instructed to ship the fecal material and diet from the previous 10 days to the laboratory for testing. Forty-one fecal samples and corresponding diets were screened for Salmonella, Clostridium perfringens, Campylobacter jejuni, Staphylococcus aureus, Staphylococcus intermedius, and pathogenic (piliated) Escherichia coli by direct culture using standard procedures. The fecal material was also screened for coronavirus and parvovirus using electron microscopy. Thirty-five "normal" fecal samples were screened for all of the above mentioned microorganisms as a control. In addition, the fecal material was screened for E. coli verotoxins I and II and clostridial enterotoxins. A total of 61 Salmonella isolates were recovered from the 41 samples of feces and diet submitted for testing; 31 were recovered from the feces and 30 from the diet. Four Salmonella isolates were recovered from the normal fecal samples. Results obtained by PCR, plasmid profiles, antigenic analysis, and antibiogram profiles indicated that 16 of the 31 isolates recovered from the fecal material were the same strain as that recovered from the diet.     

Natural Borna disease in domestic animals others than horses and sheep

In 24 cats (Uppsala, Sweden) with neurological signs of "staggering disease" and typical neuropathology, 44% had Borna disease virus (BDV)-specific antibodies. In 173 cat sera (Berlin, Germany) of animals with unknown record, 7% were BDV positive. Out of 24 cats with undefined neurological disorders, 13% were BDV positive. Similarities in staggering disease of cats and Borna disease of horses and sheep suggest related etiological agents.     

Gepulstes Heißdraht‐Vakuummeter mit Pirani‐Sensor. Pulsed hot filament vacuum gauge with Pirani sensor

The hot filament gauge according to Pirani is usually operated in the stationary mode in which the applied electrical heating power equals the total heat losses. The heat loss by the thermal conductivity of the gas increases with increasing pressure which allows to derive the measuring signal for the pressure. However, at pressures above some 100 mbar the thermal conductivity starts to saturate which results in a strong decrease of the measuring accuracy of the hot wire gauge. A few years ago, a proposal was published to make use of the heat capacity of the gas which is proportional to pressure. Subject of the present paper is a decisive investigation of the dynamical behaviour of the Pirani sensor. For this purpose, both the heating and cooling processes of the wire were measured. As follows from the experimental data and theoretical estimations, a considerable amount of energy is stored in the gas at atmospheric pressure, i.e. much more than in the wire, but this energy content has only a small effect on heating and cooling rates. Reasons for this behaviour are the strong heat losses by the thermal conductivity of the gas, the rather weak thermal coupling between the wire and surrounding as well as the smallness of the average temperature increase of the gas. Furthermore, an intermittent operation of the Pirani sensor was tested in which the voltage applied to the wire gradually increases. Advantages of this operation mode are a significant improvement of the measuring characteristics above 100 mbar and a substantial reduction of the power consumption.     

Gepulstes Pirani‐Vakuummeter: Berechnung von Aufheizung und Abkühlung. Pulsed Pirani vacuum gauge: calculation of heating and cooling

The pulsed operation of the hot filament gauge according to Pirani offers several advantages: extension of the measuring range towards larger pressures, reduced influence of the gas species, and smaller power consumption. The heating and cooling of the wire has already been experimentally investigated. However, the observed characteristics in its details can not be easily understood. In the present paper, we report on theoretical calculations of the heating and cooling processes of the sensor system consisting of wire and surrounding gas. The processes can be modelled by the Fourier differential equation of heat transport. Calculations can be performed more easily by dividing the interior of the sensor into discrete annular elements and applying the finite‐element‐method under the given boundary conditions. The results provide a quantitative and illustrative presentation of the radial temperature profile of the gas and of its time‐evolution.     

Diagnostic value of determining hemoglobin in cerebrospinal fluid in acute cerebral circulatory disorders

The results of hemoglobin determination in the CSF by the method of fluorescence microscopy in 195 patients speaks in favor of relative diagnostical importance of hemoglobin in the supra fall-out CSF for establishing the character of the stroke. The following circumstances testify to this fact: 1) in an artificial admixture of blood in the CSF in some cases there may be hemolysis of "passing" erythrocytes; 2) in a genuine admixture of blood, tests of hemoglobin in the centrifugate of the CSF may be negative since in some cases the transition of hemoglobin into bilirubin in the subarachmoid space occurs more rapidly than the hemolysis of erythrocytes. Thus, the hemoglobin does not accumulate in the liquid in quantities, sufficient enough to be measured by the existing methods; 3) in a large amount of artificial blood admixture, even without a hemolysis of "passing" erythrocytes the hemoglobin tests in the centrifugate of the CSF may be positive at the expense of hemoglobin of the blood plasma.     

Gasadsorptionschromatographie höherer Kohlenwasserstoffe. Normalparaffinbestimmung durch temperaturprogrammierte Segregations-Gaschromatographie an 5A Molekularsieb

Gas Adsorption Chromatography of Higher Hydrocarbons. Determination of Normal Paraffins by Temperature-Programmed Segregation Gas Chromatography on 5A Molecular Sieve A fast temperature program makes it possible to determine the normal paraffins up to C 20 in the concentration range between 0.1 and 99.9 percent (molecule type analysis). From the group peak of the normal paraffins we can obtain on line the distribution of the carbon numbers. As the normal paraffin selectivity of the molecular sieve S ≈ 1 can be assumed. Isoparaffin memory could not be detected. The new method makes it possible to perform analysis with great accuracy within three minutes or less. Connected to a computer it is excellently suitable for large series of samples. Under the standard conditions of this method only a little paraffin cracking has been found. Type and quantity of the cracked products proved to be independent of the chain length of the individual normal paraffin.