DDoS defense by offense

This article presents the design, implementation, analysis, and experimental evaluation of speak-up, a defense against application-level distributed denial-of-service (DDoS), in which attackers cripple a server by sending legitimate-looking requests that consume computational resources (e.g., CPU cycles, disk). With speak-up, a victimized server encourages all clients, resources permitting, to automatically send higher volumes of traffic. We suppose that attackers are already using most of their upload bandwidth so cannot react to the encouragement. Good clients, however, have spare upload bandwidth so can react to the encouragement with drastically higher volumes of traffic. The intended outcome of this traffic inflation is that the good clients crowd out the bad ones, thereby capturing a much larger fraction of the server's resources than before. We experiment under various conditions and find that speak-up causes the server to spend resources on a group of clients in rough proportion to their aggregate upload bandwidths, which is the intended result.National Science Foundation (U.S.) (NSF grant CNS-0225660)National Science Foundation (U.S.) (NSF grant CNS-0520241)United States. Dept. of Defense (National Security Science and Engineering Faculty Fellowship

XML data clustering: An overview

In the last few years we have observed a proliferation of approaches for clustering XML docu- ments and schemas based on their structure and content. The presence of such a huge amount of approaches is due to the different applications requiring the XML data to be clustered. These applications need data in the form of similar contents, tags, paths, structures and semantics. In this paper, we first outline the application contexts in which clustering is useful, then we survey approaches so far proposed relying on the abstract representation of data (instances or schema), on the identified similarity measure, and on the clustering algorithm. This presentation leads to draw a taxonomy in which the current approaches can be classified and compared. We aim at introducing an integrated view that is useful when comparing XML data clustering approaches, when developing a new clustering algorithm, and when implementing an XML clustering compo- nent. Finally, the paper moves into the description of future trends and research issues that still need to be faced

Acute Effects of Hexavalent Chromium on Survival, Oxygen Consumption, Hematological Parameters and Some Biochemical Profiles of the Indian Major Carp, Labeo rohita

An attempt has been made in the present investigation to determine the acute toxicity of hexavalent chromium and its toxicological effects on survival, physiological, hematological and biochemical parameters of the widely consumed Indian major carp, Labeo rohita. Short-term acute toxicity tests were performed adopting renewal bioassay technique (USEPA, 1975) over a period of 96h, using different concentrations of potassium dichromate to the fish and the 96 h LC50 value was found to be 111.45 mg/l (Cr+6 as 39.40 mg/l). ANOVA results showed that the normal respiratory activity of the fish was significantly affected and there is a depression in the metabolic rate at the end of 24, 48, 72 and 96h exposure. The metal also induced significant decrease (

Surface Plasmon Resonance Spectroscopy-Based High-Throughput Screening of Ligands for Use in Affinity and Displacement Chromatography

We describe an approach that uses surface plasmon resonance (SPR) spectroscopy and self-assembled monolayers (SAMs) for the high-throughput screening of ligands for use in displacement and affinity chromatographic processes. We identified a set of commercially available organic amines and allowed them to react with SAMs presenting interchain carboxylic anhydride groups; the resulting surfaces presented ligands of interest in a background of carboxylic acid groups. We used SPR spectroscopy to determine the extent of adsorption of two model proteinslysozyme and cytochrome conto these “multimodal” surfaces and to select promising “affinity” ligands for further characterization. The attachment of selected ligands to UltraLink Biosupport resulted in beads with a significantly greater affinity for lysozyme than for cytochrome c that would be suitable for use in affinity chromatographic processes. Furthermore, we also used the screens to design “affinity displacers”small molecules that selectively retain lysozyme on chromatographic resins, while displacing cytochrome c. The combination of SPR spectroscopy and SAMs represents a powerful technique for identifying novel ligands that enable the purification of complex protein mixtures