Showing papers by "Miguel Castro published in 2004"

PIC: practical Internet coordinates for distance estimation

Abstract: We introduce PIC, a practical coordinate-based mechanism to estimate Internet network distance (i.e., round-trip delay or network hops). Network distance estimation is important in many applications; for example, network-aware overlay construction and server selection. There are several proposals for distance estimation in the Internet but they all suffer from problems that limit their benefit. Most rely on a small set of infrastructure nodes that are a single point of failure and limit scalability. Others use sets of peers to compute coordinates but these coordinates can be arbitrarily wrong if one of these peers is malicious. While it may be reasonable to secure a small set of infrastructure nodes, it is unreasonable to secure all peers. PIC addresses these problems: it does not rely on infrastructure nodes and it can compute accurate coordinates even when some peers are malicious. We present PIC's design, experimental evaluation, and an application to network-aware overlay construction and maintenance.

Performance and dependability of structured peer-to-peer overlays

Abstract: Structured peer-to-peer (P2P) overlay networks provide a useful substrate for building distributed applications. They map object keys to overlay nodes and offer a primitive to send a message to the node responsible for a key. They can implement, for example, distributed hash tables and multicast trees. However, there are concerns about the performance and dependability of these overlays in realistic environments. Several studies have shown that current P2P environments have high churn rates: nodes join and leave the overlay continuously. This paper presents techniques that continuously detect faults and repair the overlay to achieve high dependability and good performance in realistic environments. The techniques are evaluated using large-scale network simulation experiments with fault injection guided by real traces of node arrivals and departures. The results show that previous concerns are unfounded; our techniques can achieve dependable routing in realistic environments with an average delay stretch below two and a maintenance overhead of less than half a message per second per node.

Defending against eclipse attacks on overlay networks

Abstract: Overlay networks are widely used to deploy functionality at edge nodes without changing network routers. Each node in an overlay network maintains pointers to a set of neighbor nodes. These pointers are used both to maintain the overlay and to implement application functionality, for example, to locate content stored by overlay nodes. If an attacker controls a large fraction of the neighbors of correct nodes, it can "eclipse" correct nodes and prevent correct overlay operation. This Eclipse attack is more general than the Sybil attack. Attackers can use a Sybil attack to launch an Eclipse attack by inventing a large number of seemingly distinct overlay nodes. However, defenses against Sybil attacks do not prevent Eclipse attacks because attackers may manipulate the overlay maintenance algorithm to mount an Eclipse attack. This paper discusses the impact of the Eclipse attack on several types of overlay and it proposes a novel defense that prevents the attack by bounding the degree of overlay nodes. Our defense can be applied to any overlay and it enables secure implementations of overlay optimizations that choose neighbors according to metrics like proximity. We present preliminary results that demonstrate the importance of defending against the Eclipse attack and show that our defense is effective.

Should we build Gnutella on a structured overlay

Abstract: There has been much interest in both unstructured and structured overlays recently. Unstructured overlays, like Gnutella, build a random graph and use flooding or random walks on the graph to discover data stored by overlay nodes. Structured overlays assign keys to data items and build a graph that maps each key to a specific node. The structure of the graph enables efficient discovery of data items given their keys but it does not support complex queries.Should we build Gnutella on a structured overlay? We believe the answer is yes. We replaced the random graph in Gnutella by a structured overlay while retaining the content placement and discovery mechanisms of unstructured overlays to support complex queries. Our preliminary results indicate that we can use structure to improve the performance of floods and rondom walks. They also indicate that structure can be used to reduce maintenance overhead, which is surprising because it is commonly believed that unstructured overlays have lower maintenance overhead than structured overlays.

Vibrational Spectroscopy Study of β and α RDX Deposits

Abstract: Deposits of β and α RDX on glass substrates have been examined with optical and Raman microscopy. The measurements reveal significant differences in the morphology and Raman spectra of β and α RDX. Structures that resemble an island, as well as scattered particles, are observed in white light images of β RDX. Well-defined crystals are observed in white light images of α RDX. The spectroscopic signature of these forms of RDX has marked differences in Raman frequencies and relative intensities. The transition from β to α RDX is driven by the amount of RDX deposited. There is a close agreement between measured and calculated vibrational frequencies for β and gas-phase RDX. A poor correlation is found between measured and predicted Raman intensities and depolarization ratios for β and gas-phase RDX, respectively. These differences lead us to conclude that the properties of β and gas phase RDX are markedly different, despite the similarities in the vibrational frequencies.

Peer-to-peer overlays: structured, unstructured, or both?

Abstract: We compare structured and unstructured overlays and derive a hybrid overlay that can outperform both. Unstructured overlays build a random graph and use flooding or random walks on that graph to discover data stored by overlay nodes. Structured overlays assign keys to data items and build a graph that maps each key to the node that stores the corresponding data. Unstructured overlays are widely used in popular applications because they can perform complex queries more efficiently than structured overlays. It is also commonly believed that structured graphs are more expensive to maintain than unstructured graphs and that the constraints imposed by the structure make it harder to exploit heterogeneity to improve scalability. This is not a fundamental problem. We describe techniques that exploit structure to achieve low maintenance overhead, and we present a modified proximity neighbor selection algorithm that can exploit heterogeneity effectively. We performed detailed comparisons of structured and unstructured graphs using simulations driven by real-world traces. Inspired by these results, we developed a hybrid system that uses the graph from structured overlays with the data placement and search strategies of unstructured overlays. The results show that our hybrid system supports complex queries more efficiently than unstructured overlays in realistic scenarios.

Can we contain Internet worms

Abstract: Worm containment must be automatic because worms can spread too fast for humans to respond. Recent work has proposed a network centric approach to automate worm containment: network traffic is analyzed to derive a packet classifier that blocks (or rate-limits) worm propagation. This approach has fundamental limitations because the analysis has no information about the application vulnerabilities exploited by worms. This paper proposes Vigilante, a new host centric approach for automatic worm containment that addresses these limitations. Vigilante relies on collaborative worm detection at end hosts in the Internet but does not require hosts to trust each other. Hosts detect worms by analysing attempts to infect applications and broadcast self-certifying alerts (SCAs) when they detect a worm. SCAs are automatically generated machine-verifiable proofs of vulnerability; they can be independently and inexpensively verified by any host. Hosts can use SCAs to generate filters or patches that prevent infection. We present preliminary results showing that Vigilante can effectively contain fast spreading worms that exploit unknown vulnerabilities.

Nucleation and crystalization studies: a vibrational-spectroscopy investigation of 2,4,6-TNT

Abstract: 2,4,6-Trinitrotoluene, commonly known as TNT, is an explosive used in military shells, bombs, landmines, grenades, demolition operations, and underwater blasting. It is produced in the United States only at military facilities. Accidental releases of TNT and residues in battle fields have contaminated groundwater, soil, and sand at numerous sites around the world. TNT exists in two physical forms at room temperature: droplets and crystals. The spectroscopic information conveyed depends on its physical form and the substrate on which it is deposited. Vibrational spectroscopy is a powerful tool that can be used to characterize TNT in its diverse forms. Crystallization of TNT from different solvents (acetonitrile, methanol, and water) was carried out to subsequently measure the vibrational spectra. The important nitroaromatic compound exhibits a series of unique characteristic bands that allow its detection and spectroscopic characterization. The spectroscopic signatures of neat TNT samples were determined with Raman Microspectroscopy and Fourier Transform Infrared (FTIR) Microscopy. The Raman spectra of neat TNT are dominated by strong bands at about 1365 and 2956 cm-1. The intensity and even the presence of these bands are found to be remarkably dependent on TNT form and source.

Spectroscopic investigation of the spectroscopic signatures of 2,4-DNT and 2,6-DNT: their interactions with sand particles

Abstract: Raman Spectroscopy is a well established tool for vibrational spectroscopy analysis. Interactions of explosives with different substrates can be measured by using quantitative vibrational signal shift information of scattered Raman light associated with these interactions. A vibrational spectroscopic study has been carried out on 2,4-DNT and 2,6-DNT crystals. Raman Microscopy spectrometers equipped with 514 nm and 785 nm laser excitation lines were used. The samples were recrystallized on different solvents (water, methanol and acetonitrile) and allowed to interact with soil samples. The interaction with sand and soil samples doped with the nitroaromatic compounds showed significant shifts in its peaks. The above information was used to detect DNT in soil using Raman Microscopy. These results will make possible the development of highly sensitive sensors for detection of explosives materials.

Spectroscopic characterization of nitroaromatic landmine signature explosives

Abstract: TNT and DNT are important explosives used as base charges of landmines and other explosive devices. They are often combined with RDX in specific explosive formulations. Their detection in vapor phase as well as in soil in contact with the explosives is important in landmine detection technology. The spectroscopic signatures of nitroaromatic compounds in neat forms: crystals, droplets, and recrystallized samples were determined by Raman Microspectroscopy (RS), Fourier Transform Infrared Microscopy (FTIR) and Fiber Optics Coupled - Fourier Transform Infrared Spectroscopy (FOC-FTIR) using a grazing angle (GA) probe. TNT exhibits a series of characteristic bands: vibrational signatures, which allow its detection in soil. The spectroscopic signature of neat TNT is dominated by strong bands about 1380 and 2970 cm -1 . The intensity and position of these bands were found remarkably different in soil samples spiked with TNT. The 1380 cm -1 band is split into a number of bands in that region. The 2970 cm -1 band is reduced in intensity and new bands are observed about 2880 cm -1 . The results are consistent with a different chemical environment of TNT in soil as compared to neat TNT. Interactions were found to be dependent on the physical source of the explosive. In the case of DNT-sand interactions, shifts in vibrational frequencies of the explosives as well as the substrates were found.

Proceedings of the 11th workshop on ACM SIGOPS European workshop

Abstract: The 11th ACM SIGOPS European Workshop will take place in Leuven (near Brussels), Belgium, from September 19th to September 22nd 2004.Leuven is one of Europe's ancient university towns with many old beautiful buildings. The town hall, the famous Beguinage (Begijnhof), the churches, cloisters and colleges stand silent witness to the rich history of Leuven and make it the interesting place it is. Leuven is only 25 km (15 miles) away from Brussels, the capital of Belgium and the centre of the European Union.The Conference will take place in the unique setting of the Beguine Convent, the "Groot Begijnhof", situated at the south edge of Leuven.

Adsorption of RDX on clay

Abstract: The chemical spectroscopic signature of the RDX-clay mineral complex has been investigated by means of reflectance FT-IR micro spectroscopy. The mechanical analysis method was used to separate the clay from the other soil components. The soil was obtained from the University of Puerto Rico at Mayaguez (UPRM) campus backyard. B3LYP/6-311G** calculations performed on RDX helped to determine the most stable conformations, their symmetry, and vibrational spectra. The FTIR technique confirmed the existence of two different RDX solid phases, known as the α-RDX and β-RDX, which have different symmetries and revealed significant differences in their spectra. The IR microspectroscopic study showed that the RDX-clay mineral complex and its interactions can be detected using the FTIR technique at a low concentration of 1000 part-per-millions. The results also suggest that the vibrational modes presenting changes in the different vibrational spectra correspond to the C-N and NO 2 groups. In comparison with α-RDX spectrum, the complex exhibits three bands at 740, 754 and 792 cm -1 . A 12 cm -1 red shift is observed in this last band assign to the C-N stretching and NO 2 scissoring vibrations in the equatorial position. Differences in the spectra were also seen in the shifted bands at 942 and 953 cm -1 . These vibrational modes are assigned to the ring breathing and N-N stretching vibration in the axial position for the -phase. Comparison of the spectra of the α-RDX, the β-RDX and the RDX mixed with clay in the range from 1190 to 1700 cm -1 clearly indicated that the FTIR technique can be used to study the interaction between RDX and clay. The results also indicate that the interaction between the RDX and the clay minerals affects mainly the NO 2 groups of the explosive molecules. It is suggested that the electron donor nitrogen atoms from RDX are interacting with the electron acceptor oxygen atoms of the siloxane surface that is present in the majority of clays.

Imaging and characterization of aerosol-deposited TNT nanoparticles: a near-field optical microscopy study

Abstract: Trace detection of energetic materials has turned into a continuously growing field of interest for environmental and security reasons. The spectroscopic and imaging characterization of these materials at trace level play a major role in the development of sensing devices that enable their detection. In this work, the synthesis and imaging characterization of TNT particles over glass and gold substrates is performed. TNT solution in HPLC grade solvent was utilized as an aerosol jet coupled to a crossed beam of nitrogen gas to dry the aerosol during the path to the glass surface. Two different temperatures were set for the drier gas, 293 and 328 K. Atomic force microscopy (AFM), near field optical microscopy (NSOM), and scanning electron microscopy (SEM) reveal that a hot aerosol jet of TNT produced the smaller particles of these materials. TNT deposits resemble liquid like droplets with an ellipsoidal shape. TNT droplets prepared at room temperature and 320 K were (1736 ± 600) and (1379 ± 503)nm in diameter, respectively. The spectroscopic measurements revealed that nanosized formations correspond with TNT signature.

Femtosecond laser UV photochemistry of TNT deposits: the role of hydroxyls

Abstract: The photochemistry of TNT in toluene, water and methanol has been studied with femtosecond laser spectroscopy, surface reflection Fourier transform infrared absorption spectroscopy and ultraviolet-visible absorption spectroscopy measurements. Aqueous and alcoholic TNT solutions change from colorless to yellow or red upon irradiation with ultrafast 266.7 nm laser pulses. Irradiated aqueous or alcoholic TNT solutions exhibit increased absorption of light above 300 nm. Surface reflection FTIR measurements of dry deposits of irradiated samples are consistent with the formation of amines or alcohols in the photochemistry of TNT in aqueous or alcoholic solutions. In contrast, no evidence is observed in post irradiation UV-visible absorption or surface reflection FTIR measurements of TNT in toluene samples exposed to 266.7 nm femtosecond laser pulses. The results suggest that the hydroxyl group is involved in the formation of photoproducts of TNT photolysis. In addition, the results suggest that femtosecond laser photolysis is suitable for TNT detection in wet media.