260 research outputs found
CONSTRUCTION OF EFFICIENT AUTHENTICATION SCHEMES USING TRAPDOOR HASH FUNCTIONS
In large-scale distributed systems, where adversarial attacks can have widespread impact, authentication provides protection from threats involving impersonation of entities and tampering of data. Practical solutions to authentication problems in distributed systems must meet specific constraints of the target system, and provide a reasonable balance between security and cost. The goal of this dissertation is to address the problem of building practical and efficient authentication mechanisms to secure distributed applications. This dissertation presents techniques to construct efficient digital signature schemes using trapdoor hash functions for various distributed applications. Trapdoor hash functions are collision-resistant hash functions associated with a secret trapdoor key that allows the key-holder to find collisions between hashes of different messages. The main contributions of this dissertation are as follows:
1. A common problem with conventional trapdoor hash functions is that revealing a collision producing message pair allows an entity to compute additional collisions without knowledge of the trapdoor key. To overcome this problem, we design an efficient trapdoor hash function that prevents all entities except the trapdoor key-holder from computing collisions regardless of whether collision producing message pairs are revealed by the key-holder.
2. We design a technique to construct efficient proxy signatures using trapdoor hash functions to authenticate and authorize agents acting on behalf of users in agent-based computing systems. Our technique provides agent authentication, assurance of agreement between delegator and agent, security without relying on secure communication channels and control over an agent’s capabilities.
3. We develop a trapdoor hash-based signature amortization technique for authenticating real-time, delay-sensitive streams. Our technique provides independent verifiability of blocks comprising a stream, minimizes sender-side and receiver-side delays, minimizes communication overhead, and avoids transmission of redundant information.
4. We demonstrate the practical efficacy of our trapdoor hash-based techniques for signature amortization and proxy signature construction by presenting discrete log-based instantiations of the generic techniques that are efficient to compute, and produce short signatures.
Our detailed performance analyses demonstrate that the proposed schemes outperform existing schemes in computation cost and signature size. We also present proofs for security of the proposed discrete-log based instantiations against forgery attacks under the discrete-log assumption
Extrapolation of post-harvest soil test values in barnyard millet-based cropping sequence through multivariate analysis
The soil test value is based on the soil test-based fertilizer prescription/ recommendation equation. Each crop harvesting after the next crop is necessary to analyze the soil. Therefore, it is necessary to develop an alternative technique to predict postharvest soil tests after the harvest of every crop. For that a study was conducted in mixed black calcareous soils at Tamil Nadu agricultural University, Coimbatore to develop the post-harvest prediction equations for available nitrogen, phosphorus and potassium in barnyard millet cropping sequence based on a multiple regression model by considering post-harvest soil test value as the dependent variable and initial available nutrients, fertilizer doses and crop yield or crop nutrient uptake as an independent variables. The developed model was validated by computing R2 value, RMSE (root means square error), RE (relative error), and the ratio of performance to deviation (RPD) and the developed model was found to be valid. Using the validated model, post-harvest soil test values were predicted. A fertilizer recommendation was made for blackgram based on predicted post-harvest soil test values in the barnyard millet-blackgram cropping sequence. The predicted soil test values were compared with actual soil test values and it revealed that the developed model is fairly accurate and best-fitted with more precision. The predicted post-harvest soil test values of barnyard millet could be used in order to prescribe fertilizer for desired yield targets for subsequent crops
Secondary crystalline phases identification in Cu2ZnSnSe4 thin films: contributions from Raman scattering and photoluminescence
In this work, we present the Raman peak
positions of the quaternary pure selenide compound
Cu2ZnSnSe4 (CZTSe) and related secondary phases that
were grown and studied under the same conditions. A vast
discussion about the position of the X-ray diffraction
(XRD) reflections of these compounds is presented. It is
known that by using XRD only, CZTSe can be identified
but nothing can be said about the presence of some secondary
phases. Thin films of CZTSe, Cu2SnSe3, ZnSe,
SnSe, SnSe2, MoSe2 and a-Se were grown, which allowed
their investigation by Raman spectroscopy (RS). Here we
present all the Raman spectra of these phases and discuss
the similarities with the spectra of CZTSe. The effective
analysis depth for the common back-scattering geometry
commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated
for different wavelength values. The observed
asymmetric PL band on a CZTSe film is compatible with
the presence of CZTSe single-phase and is discussed in the
scope of the fluctuating potentials’ model. The estimated
bandgap energy is close to the values obtained from
absorption measurements. In general, the phase identification
of CZTSe benefits from the contributions of RS and
PL along with the XRD discussion.info:eu-repo/semantics/publishedVersio
Variations in the copper(I)-copper(I) distances in multinuclear clusters with identical coordination geometries. Short metal-metal contacts induced by oligomerization
Factors contributing to the variations in the Cu(I)-Cu(I) distances in two clusters with identical ligand and coordination geometries have been analyzed. While the hexamer, 4, exhibits metal-metal distances in the range 2.81-3.25 Angstrom, shorter contacts are found in the corresponding tetramer, 3 (2.60-2.77 Angstrom). EHT calculations reveal relatively little attractive interactions in the corresponding Cu-4(4+) and Cu-6(6+) cores. Introduction of the ligands lowers the reduced overlap populations between the metals further. MNDO calculations with model electrophiles have been carried out to determine the bite angle requirements of the ligands. These are satisfactorily met in the structures of both 3 and 4. The key geometric feature distinguishing 3 and 4 is the Cu-S-Cu angle involving the bridging S- unit. In 4, the corresponding angles are about 90 degrees, while the values in 3 are smaller (70-73 degrees). Wider angles are computed to be energetically favored and are characterized by an open three-center bond and a long Cu-Cu distance. The bridging angles are suggested to be primarily constrained by the mode of oligomerization. Implications of these results for the stability and reactivity of these clusters and for short metal-metal distances in d(10) systems in general are discussed
A Novel Method for Feature Identification of Proteins
With a rapidly growing database of protein structures, one needs fast algorithms for comparison of two protein structures, based on an efficient representation of a protein. As such, the problem has exponential time complexity, which is prohibitive if one has to perform the comparison at the residue level. One needs efficient representation methods to compare 3-D patterns of residues. In this paper, we propose the use of nearest-neighbour clustering as an efficient means to find out higher-level features in a large database of proteins. We also propose a method to estimate the optimal size of a biologically significant feature
Distinctive microRNA signature of medulloblastomas associated with the WNT signaling pathway
Aim: Medulloblastoma is a malignant brain tumor that occurs
predominantly in children. Current risk stratification based on
clinical parameters is inadequate for accurate prognostication.
MicroRNA expression is known to be deregulated in various cancers and
has been found to be useful in predicting tumor behavior. In order to
get a better understanding of medulloblastoma biology, miRNA profiling
of medulloblastomas was carried out in parallel with expression
profiling of protein-coding genes. Materials and Methods: miRNA
profiling of medulloblastomas was carried out using Taqman Low Density
Array v 1.0 having 365 human microRNAs. In parallel, genome-wide
expression profiling of protein-coding genes was carried out using
Affymetrix gene 1.0 ST arrays. Results: Both the profiling studies
identified four molecular subtypes of medulloblastomas. Expression
levels of select protein-coding genes and miRNAs could classify an
independent set of medulloblastomas. Twelve of 31 medulloblastomas were
found to overexpress genes belonging to the canonical WNT signaling
pathway and carry a mutation in CTNNB1 gene. A number of miRNAs like
miR-193a, miR-224/miR-452 cluster, miR-182/miR-183/miR-96 cluster, and
miR-148a having potential tumor/metastasis suppressive activity were
found to be overexpressed in the WNT signaling associated
medulloblastomas. Exogenous expression of miR-193a and miR-224, two
miRNAs that have the highest WNT pathway specific upregulation, was
found to inhibit proliferation, increase radiation sensitivity and
reduce anchorage-independent growth of medulloblastoma cells.
Conclusion: Expression level of tumor/metastasis suppressive miRNAs in
the WNT signaling associated medulloblastomas is likely to determine
their response to treatment, and thus, these miRNAs would be important
biomarkers for risk stratification within the WNT signaling associated
medulloblastomas
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