During the rapid development of mobile wireless technologies and applications, the Android operating system, due to its open-source characteristics, has become the most popular development platform in the smartphone market. Meanwhile, as Android-based intelligent mobiles devices experience a rapid increase in numbers, high-tech crimes involving such devices have become more versatile, affecting an ever increasing amount of data, thus making digital evidence an indispensable part of the evidence that needs to be seriously dealt with during crime investigations. Consequently, understanding the internal structure of Android and the various data operations in the file systems becomes necessary in Android-based digital forensics. In this paper, we survey the state-of-the-art of technologies in Android-based digital forensics and some popular tools in the aspects of data recovery and acquisition, file system analysis and data analysis. We also discuss some technical challenges and point out future research directions in Android-based digital forensics.
Purpose
Retinal pigment epithelium (RPE) degeneration is a leading cause of blindness in retinal degenerative diseases, but the mechanism of RPE regional degeneration remains largely unknown. This study aims to investigate the sensitivity of RPE to sodium iodate (SI) injury in the dorsal and ventral visual fields in mice and analyze whether overlaying cone photoreceptors regulate the sensitivity of RPE to SI-induced damage.
Methods
SI was used to induce RPE degeneration in mice. Hematoxylin-eosin staining, immunostaining, and TUNEL assay were used to evaluate retinal degeneration along the dorsal-ventral axis. Flat-mounted and sectional retinal immunostaining were used to analyze the distribution of cones along the dorsoventral axis in C57BL/6, albino, and 129 mice. Electroretinography was used to examine the retinal function.
Results
Dorsal-central RPE was more sensitive to SI-mediated injury along the dorsal-ventral axis in C57BL/6 mice. Compared with the ventral RPE, the dorsal-central RPE was dominantly covered by M cone photoreceptors in these mice. Interestingly, M cone photoreceptor degeneration was followed by dorsal RPE degeneration under a low dose of SI. Furthermore, the sensitivity of dorsal RPE to a low dose of SI was reduced in both albino and 129 mouse strains with dominant mixed cones instead of M cones in the dorsal visual field.
Conclusions
These findings suggest that dorsal-central RPE is more sensitive to SI injury and that SI-induced RPE degeneration could be controlled by modifying the dominant overlying cone population in the mouse dorsal retina, thereby highlighting a potential role of M cones in RPE regional degeneration.
Data recovery from captured intelligent mobile devices such as smartphones plays a significant role in digital forensic analysis. In this paper, we study the main characteristics of NAND flash and YAFFS2 file systems and explore the method for recovering YAFFS2 files for forensic analysis based on Tnode tree that can save a lot of time compared to other data recovery methods. For any broken file that has missing or broken data pages, we propose to reuse pages from previous versions of the current file based on the chunk IDs of the missing pages to replace and thus recover such pages. We will describe the replacement method with detailed steps and also perform some analysis to show that the proposed replacement approach can be feasible and effective in reconstructing YAFFS2 files.
As Android-based intelligent devices get more popular, digital technologies for forensic investigation have received increasingly more attention. Among the main technical issues in digital forensics, however, data recovery requires a significant amount of effort. In this paper, we first analyze the characteristics of the NAND flash storage as well as the mechanisms in the YAFFS2 file system. We then propose a file reconstruction method based on timestamps using Tnode trees in the YAFFS2 file system. Based on the last access timestamp information in the object header and the process of creating Tnode tree, the proposed method can be used to locate valid data blocks so as to recover the original files and would thus be able to reconstruct the file system. Experiments conducted under the Linux operating system over image files show that the proposed method could recover the final version of files effectively and would also perform more efficiently compared to similar methods.
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