The χ^2 family of signal fluctuation distributions represents the main fluctuation models which most radar targets follow it in their reflections. This family can be categorized as fluctuation distribution with two d...The χ^2 family of signal fluctuation distributions represents the main fluctuation models which most radar targets follow it in their reflections. This family can be categorized as fluctuation distribution with two degrees of freedom and those with four degrees of freedom. The first category represents all important class of fluctuation models which when illuminated by a coherent pulse train, return a train of fully correlated pulses （Swerling Ⅰ model） or fully decorrelated pulses （Swerling Ⅱ model）. The detection of this type of fluctuating targets is therefore of great importance. This paper is devoted to the analysis of Cell-Averaging （CA） based detectors for the case where the radar receiver noncoherently integrates M square-law detected pulses and the signal fluctuation obeys 2 statistics with two degrees of freedom. These detectors include the Mean-Of （MO）, the Greatest-Of （GO） and the Smallest-Of（SO） schemes. In these processors, the estimation of the noise power levels from the leading and the trailing reference windows is based on the CA technique. Exact formulas for the detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the χ^2 fluctuation model with two degrees of freedom （SWI ＆ SWII）. The numerical results show that the MO version has the best homogeneous performance, the SO scheme has the best multiple-target performance, while the GO procedure does not offer any merits, neither in the absence nor in the presence of outlying targets.展开更多
Access control mechanisms are widely used in multi-user IT systems where it is necessary to restrict access to computing resources.This is certainly true of file systems whereby information needs to be protected again...Access control mechanisms are widely used in multi-user IT systems where it is necessary to restrict access to computing resources.This is certainly true of file systems whereby information needs to be protected against unintended access.User permissions often evolve over time,and changes are often made in an ad hoc manner and do not follow any rigorous process.This is largely due to the fact that the structure of the implemented permissions are often determined by experts during initial system configuration and documentation is rarely created.Furthermore,permissions are often not audited due to the volume of information,the requirement of expert knowledge,and the time required to perform manual analysis.This paper presents a novel,unsupervised technique whereby a statistical analysis technique is developed and applied to detect instances of permission creep.The system(herein refereed to as Creeper)has initially been developed for Microsoft systems;however,it is easily extensible and can be applied to other access control systems.Experimental analysis has demonstrated good performance and applicability on synthetic file system permissions with an average accuracy of 96%.Empirical analysis is subsequently performed on five real-world systems where an average accuracy of 98%is established.展开更多
Access control mechanisms are widely used in multi-user IT systems where it is necessary to restrict access to computing resources.This is certainly true of file systems whereby information needs to be protected again...Access control mechanisms are widely used in multi-user IT systems where it is necessary to restrict access to computing resources.This is certainly true of file systems whereby information needs to be protected against unintended access.User permissions often evolve over time,and changes are often made in an ad hoc manner and do not follow any rigorous process.This is largely due to the fact that the structure of the implemented permissions are often determined by experts during initial system configuration and documentation is rarely created.Furthermore,permissions are often not audited due to the volume of information,the requirement of expert knowledge,and the time required to perform manual analysis.This paper presents a novel,unsupervised technique whereby a statistical analysis technique is developed and applied to detect instances of permission creep.The system(herein refereed to as Creeper)has initially been developed for Microsoft systems;however,it is easily extensible and can be applied to other access control systems.Experimental analysis has demonstrated good performance and applicability on synthetic file system permissions with an average accuracy of 96%.Empirical analysis is subsequently performed on five real-world systems where an average accuracy of 98% is established.展开更多
文摘The χ^2 family of signal fluctuation distributions represents the main fluctuation models which most radar targets follow it in their reflections. This family can be categorized as fluctuation distribution with two degrees of freedom and those with four degrees of freedom. The first category represents all important class of fluctuation models which when illuminated by a coherent pulse train, return a train of fully correlated pulses （Swerling Ⅰ model） or fully decorrelated pulses （Swerling Ⅱ model）. The detection of this type of fluctuating targets is therefore of great importance. This paper is devoted to the analysis of Cell-Averaging （CA） based detectors for the case where the radar receiver noncoherently integrates M square-law detected pulses and the signal fluctuation obeys 2 statistics with two degrees of freedom. These detectors include the Mean-Of （MO）, the Greatest-Of （GO） and the Smallest-Of（SO） schemes. In these processors, the estimation of the noise power levels from the leading and the trailing reference windows is based on the CA technique. Exact formulas for the detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the χ^2 fluctuation model with two degrees of freedom （SWI ＆ SWII）. The numerical results show that the MO version has the best homogeneous performance, the SO scheme has the best multiple-target performance, while the GO procedure does not offer any merits, neither in the absence nor in the presence of outlying targets.
基金This work was undertaken during a project funded by the UK’s Digital Catapult Researcher in Residency Fellowship programme(Grant Ref:EP/M029263/1).The funding supported the research,development,and empirical testing presented in this paper.
文摘Access control mechanisms are widely used in multi-user IT systems where it is necessary to restrict access to computing resources.This is certainly true of file systems whereby information needs to be protected against unintended access.User permissions often evolve over time,and changes are often made in an ad hoc manner and do not follow any rigorous process.This is largely due to the fact that the structure of the implemented permissions are often determined by experts during initial system configuration and documentation is rarely created.Furthermore,permissions are often not audited due to the volume of information,the requirement of expert knowledge,and the time required to perform manual analysis.This paper presents a novel,unsupervised technique whereby a statistical analysis technique is developed and applied to detect instances of permission creep.The system(herein refereed to as Creeper)has initially been developed for Microsoft systems;however,it is easily extensible and can be applied to other access control systems.Experimental analysis has demonstrated good performance and applicability on synthetic file system permissions with an average accuracy of 96%.Empirical analysis is subsequently performed on five real-world systems where an average accuracy of 98%is established.
基金undertaken during a project funded by the UK’s Digital Catapult Researcher in Residency Fellowship programme(Grant Ref:EP/M029263/1).
文摘Access control mechanisms are widely used in multi-user IT systems where it is necessary to restrict access to computing resources.This is certainly true of file systems whereby information needs to be protected against unintended access.User permissions often evolve over time,and changes are often made in an ad hoc manner and do not follow any rigorous process.This is largely due to the fact that the structure of the implemented permissions are often determined by experts during initial system configuration and documentation is rarely created.Furthermore,permissions are often not audited due to the volume of information,the requirement of expert knowledge,and the time required to perform manual analysis.This paper presents a novel,unsupervised technique whereby a statistical analysis technique is developed and applied to detect instances of permission creep.The system(herein refereed to as Creeper)has initially been developed for Microsoft systems;however,it is easily extensible and can be applied to other access control systems.Experimental analysis has demonstrated good performance and applicability on synthetic file system permissions with an average accuracy of 96%.Empirical analysis is subsequently performed on five real-world systems where an average accuracy of 98% is established.
