Unidade de Investigação - CIIC - Computer Science and Communication Research Centre
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Percorrer Unidade de Investigação - CIIC - Computer Science and Communication Research Centre por Objetivos de Desenvolvimento Sustentável (ODS) "11:Cidades e Comunidades Sustentáveis"
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- Explaining the seismic moment of large earthquakes by heavy and extremely heavy tailed modelsPublication . Felgueiras, Miguel MartinsThe search of physical laws that explain the energy released by the great magnitude earthquakes is a relevant question, since as a rule they cause heavy losses. Several statistical distributions have been considered in this process, namely heavy tailed laws, like the Pareto distribution with shape parameter α ≈ 0. 6667. Yet, for the usually considered Californian region (where earthquakes with moment magnitude, MW, greater than 7. 9 were never registered) the Pareto distribution with index near the above mentioned seems to have a "too heavy" tail for explaining the bigger earthquakes seismic moments. Usually an exponential tapper is applied to the distribution right tail (above the so called corner seismic moment), or another distribution is considered to explain these high seismic moment data (like another Pareto with different shape parameter). The situation is different for other regions where seisms of larger magnitudes do occur, leading to data sets for which heavy or even extremely heavy tailed models are appropriated. The purpose of this paper is to reduce the seismic moment, M0, of the very large earthquakes to particular heavy and extremely heavy tailed distributions. Using world seismic moment information, we apply Pareto, Log-Pareto and extended slash Pareto distributions to the data, truncated for M0 ≥ 1021 Nm and for M0 ≥ 1021. 25 Nm. For these great seisms we conclude that extended slash Pareto is a promising alternative to the more traditional Pareto and Log-Pareto distributions as a candidate to the real model underlying the data.
- Filtering Email Addresses, Credit Card Numbers and Searching for Bitcoin Artifacts with the Autopsy Digital Forensics SoftwarePublication . Domingues, Patricio; Frade, Miguel; Parreira, João MotaEmail addresses and credit card numbers found on digital forensic images are frequently an important asset in a forensic casework. However, the automatic harvesting of these data often yields many false positives. This paper presents the Forensic Enhanced Analysis (FEA) module for the Autopsy digital forensic software. FEA aims to eliminate false positives of email addresses and credit card numbers harvested by Autopsy, thus reducing the workload of the forensic examiner. FEA also harvests potential Bitcoin public addresses and private keys and validates them by looking into Bitcoin’s blockchain for the transactions linked to public addresses. FEA explores the report functionality of Autopsy and allows exports in CSV, HTML and XLS formats. Experimental results over four digital forensic images show that FEA eliminates as many as of email addresses and of credit card numbers.
- Keeping track of UWP application changes for digital forensic purposesPublication . Andrade, Luis Miguel; Domingues, Patricio; Frade, MiguelDigital forensics aims to collect and interpret artifacts that can help in the understanding of the action performed by a given individual or organization. The forensic artifacts are highly dependent on the inner working of the operating system (OS) and applications. This is the case for applications of the Universal Windows Platform (UWP), with digital forensic practitioners often depending on the data kept in the private database(s) of the application. However, some of these applications evolve rapidly, with new versions bringing changes that sometimes involve their inner databases and thus might impact digital forensic artifacts. In this paper, we present UWPscanner, an open source system that we have developed. The UWPscanner system allows to track the changes of internal databases used by UWP applications, aiming to ease the task of not only digital practitioners, but also of digital forensic tool developers. The paper is complemented with the case-study of tracking Microsoft Skype (SkypeApp) and Your Phone evolution with UWPscanner.
- Perfect Periodic Sequences with Low PAPRPublication . Ferreira, M.; Gasparovic, M.; Manjunath, G.; Priem-Mendes, S.; Pereira, J. S.Different coding sequences have huge effects on the performance of Code Division Multiple Access and Orthogonal Frequency Division Multiple Access communication systems. We propose new perfect sequences, derived from an Inverse Discrete Fourier Transform of Golay codes, and present both a mathematical and hardware-based direct/inverse generator for these new sequences. Our analysis reveals that these new sequences, named Orthogonal Perfect DFT Golay (OPDG) codes, have better autocorrelation and cross-correlation properties than the Golay codes. High Peak-to-Average Power Ratio (PAPR) is identified as one of the main practical problems involving Orthogonal Frequency Division Multiple Access power transmission. To minimize this problem, we introduce a bipolar decomposition of our new perfect sequences that permit the lowest PAPR (equal to 1) for each of the new bipolar codes. Additionally, this paper shows that the new bipolar codes derived from OPDG sequences outperform orthogonal Gold codes regarding error transmission probabilities.