Reverse engineering of ReFS

File system forensics is an important part of Digital Forensics. Investigators of storage media have traditionally focused on the most commonly used file systems such as NTFS, FAT, ExFAT, Ext2-4, HFS+, APFS, etc. NTFS is the current file system used by Windows for the system volume, but this may change in the future. In this paper we will show the structure of the Resilient File System (ReFS), which has been available since Windows Server 2012 and Windows 8. The main purpose of ReFS is to be used on storage spaces in server systems, but it can also be used in Windows 8 or newer. Although ReFS is not the current standard file system in Windows, while users have the option to create ReFS file systems, digital forensic investigators need to investigate the file systems identified on a seized media. Further, we will focus on remnants of non-allocated metadata structures or attributes. This may allow metadata carving, which means searching for specific attributes that are not allocated. Attributes found can then be used for file recovery. ReFS uses superblocks and checkpoints in addition to a VBR, which is different from other Windows file systems. If the partition is reformatted with another file system, the backup superblocks can be used for partition recovery. Further, it is possible to search for checkpoints in order to recover both metadata and content.Another concept not seen for Windows file systems, is the sharing of blocks. When a file is copied, both the original and the new file will share the same content blocks. If the user changes the copy, new data runs will be created for the modified content, but unchanged blocks remain shared. This may impact file carving, because part of the blocks previously used by a deleted file might still be in use by another file. The large default cluster size, 64 KiB, in ReFS v1.2 is an advantage when carving for deleted files, since most deleted files are less than 64 KiB and therefore only use a single cluster. For ReFS v3.2 this advantage has decreased because the standard cluster size is 4 KiB.Preliminary support for ReFS v1.2 has been available in EnCase 7 and 8, but the implementation has not been documented or peer-reviewed. The same is true for Paragon Software, which recently added ReFS support to their forensic product. Our work documents how ReFS v1.2 and ReFS v3.2 are structured at an abstraction level that allows digital forensic investigation of this new file system. At the time of writing this paper, Paragon Software is the only digital forensic tool that supports ReFS v3.x.It is the most recent version of the ReFS file system that is most relevant for digital forensics, as Windows automatically updates the file system to the latest version on mount. This is why we have included information about ReFS v3.2. However, it is possible to change a registry value to avoid updating. The latest ReFS version observed is 3.4, but the information presented about 3.2 is still valid. In any criminal case, the investigator needs to investigate the file system version found.     

Structure and application of IconCache.db files for digital forensics

Anti-forensics has developed to prevent digital forensic investigations, thus forensic investigations to prevent anti-forensic behaviors have been studied in various area. In the area of user activity analysis, “IconCache.db” files contain icon cache information related to applications, which can yield meaningful information for digital forensic investigations such as the traces of deleted files. A previous study investigated the general artifacts found in the IconCache.db file. In the present study, further features and structures of the IconCache.db file are described. We also propose methods for analyzing anti-forensic behaviors (e.g., time information related to the deletion of files). Finally, we introduce an analytical tool that was developed based on the file structure of IconCache.db. The tool parses out strings from the IconCache.db to assist an analyst. Therefore, an analyst can more easily analyze the IconCache.db file using the tool.     

Using the HFS+ journal for deleted file recovery

This paper describes research and analysis that were performed to identify a robust and accurate method for identifying and extracting the residual contents of deleted files stored within an HFS+ file system. A survey performed during 2005 of existing tools and techniques for HFS+ deleted file recovery reinforced the need for newer, more accurate techniques.Our research and analysis were based on the premise that a transactional history of file I/O operations is maintained in a Journal on HFS+ file systems, and that this history could be used to reconstruct recent deletions of active files from the file system. Such an approach offered a distinct advantage over other current techniques, including recovery of free/unallocated blocks and “file carving” techniques. If the journal entries contained or referenced file attributes such as the extents that specify which file system blocks were occupied by each file, then a much more accurate identification and recovery of deleted file data would be possible.     

Using the HFS+ journal for deleted file recovery

This paper describes research and analysis that were performed to identify a robust and accurate method for identifying and extracting the residual contents of deleted files stored within an HFS+ file system. A survey performed during 2005 of existing tools and techniques for HFS+ deleted file recovery reinforced the need for newer, more accurate techniques.Our research and analysis were based on the premise that a transactional history of file I/O operations is maintained in a Journal on HFS+ file systems, and that this history could be used to reconstruct recent deletions of active files from the file system. Such an approach offered a distinct advantage over other current techniques, including recovery of free/unallocated blocks and “file carving” techniques. If the journal entries contained or referenced file attributes such as the extents that specify which file system blocks were occupied by each file, then a much more accurate identification and recovery of deleted file data would be possible.     

Bin-Carver: Automatic recovery of binary executable files

File carving is the process of reassembling files from disk fragments based on the file content in the absence of file system metadata. By leveraging both file header and footer pairs, traditional file carving mainly focuses on document and image files such as PDF and JPEG. With the vast amount of malware code appearing in the wild daily, recovery of binary executable files becomes an important problem, especially for the case in which malware deletes itself after compromising a computer. However, unlike image files that usually have both a header and footer pair, executable files only have header information, which makes the carving much harder. In this paper, we present Bin-Carver, a first-of-its-kind system to automatically recover executable files with deleted or corrupted metadata. The key idea is to explore the road map information defined in executable file headers and the explicit control flow paths present in the binary code. Our experiment with thousands of binary code files has shown our Bin-Carver to be incredibly accurate, with an identification rate of 96.3% and recovery rate of 93.1% on average when handling file systems ranging from pristine to chaotic and highly fragmented.     

Forensic artefacts left by Pidgin Messenger 2.0

Pidgin, formerly known as Gaim, is a multi-protocol instant messaging (IM) client that supports communication on most of the popular IM networks. Pidgin is chiefly popular under Linux, and is available for Windows, BSD and other UNIX versions. This article presents a number of traces that are left behind after the use of Pidgin on Linux, enabling digital investigators to search for and interpret instant messaging activities, including online conversations and file transfers. Specifically, the contents and structures of user settings, log files, contact files and the swap partition are discussed. In addition looking for such information in active files on a computer, forensic examiners can recover deleted items by searching a hard drive for file signatures and known file structures detailed in this article.     

A novel file carving algorithm for National Marine Electronics Association (NMEA) logs in GPS forensics

Globe positioning system (GPS) devices are an increasing importance source of evidence, as more of our devices have built-in GPS capabilities. In this paper, we propose a novel framework to efficiently recover National Marine Electronics Association (NMEA) logs and reconstruct GPS trajectories. Unlike existing approaches that require file system metadata, our proposed algorithm is designed based on the file carving technique without relying on system metadata. By understanding the characteristics and intrinsic structure of trajectory data in NMEA logs, we demonstrate how to pinpoint all data blocks belonging to the NMEA logs from the acquired forensic image of GPS device. Then, a discriminator is presented to determine whether two data blocks can be merged. And based on the discriminator, we design a reassembly algorithm to re-order and merge the obtained data blocks into new logs. In this context, deleted trajectories can be reconstructed by analyzing the recovered logs. Empirical experiments demonstrate that our proposed algorithm performs well when the system metadata is available/unavailable, log files are heavily fragmented, one or more parts of the log files are overwritten, and for different file systems of variable cluster sizes.     

Carving contiguous and fragmented files with fast object validation

“File carving” reconstructs files based on their content, rather than using metadata that points to the content. Carving is widely used for forensics and data recovery, but no file carvers can automatically reassemble fragmented files. We survey files from more than 300 hard drives acquired on the secondary market and show that the ability to reassemble fragmented files is an important requirement for forensic work. Next we analyze the file carving problem, arguing that rapid, accurate carving is best performed by a multi-tier decision problem that seeks to quickly validate or discard candidate byte strings – “objects” – from the media to be carved. Validators for the JPEG, Microsoft OLE (MSOLE) and ZIP file formats are discussed. Finally, we show how high speed validators can be used to reassemble fragmented files.     

电子取证中AVI文件的文件雕复

用电子取证中的文件雕复相关技术,并以AVI文件为实例,阐述一种侦测AVI文件碎片,并将碎片排序组合成完整文件的文件雕复方法。通过实例的文件雕复方法基于AVI文件格式的结构特征,借鉴了文件结构关键字匹配,二分碎片间隙雕复等文件雕复思想来完成实验。此方法能在失去系统元信息的情况下完成对AVI文件的文件雕复。实验结果表明,此方法提高了有碎片的AVI文件的雕复成功率。     

The Prevalence of Encoded Digital Trace Evidence in the Nonfile Space of Computer Media,,

Forensically significant digital trace evidence that is frequently present in sectors of digital media not associated with allocated or deleted files. Modern digital forensic tools generally do not decompress such data unless a specific file with a recognized file type is first identified, potentially resulting in missed evidence. Email addresses are encoded differently for different file formats. As a result, trace evidence can be categorized as Plain in File (PF), Encoded in File (EF), Plain Not in File (PNF), or Encoded Not in File (ENF). The tool bulk_extractor finds all of these formats, but other forensic tools do not. A study of 961 storage devices purchased on the secondary market and shows that 474 contained encoded email addresses that were not in files (ENF). Different encoding formats are the result of different application programs that processed different kinds of digital trace evidence. Specific encoding formats explored include BASE64, GZIP, PDF, HIBER, and ZIP.     

Detecting file fragmentation point using sequential hypothesis testing

File carving is a technique whereby data files are extracted from a digital device without the assistance of file tables or other disk meta-data. One of the primary challenges in file carving can be found in attempting to recover files that are fragmented. In this paper, we show how detecting the point of fragmentation of a file can benefit fragmented file recovery. We then present a sequential hypothesis testing procedure to identify the fragmentation point of a file by sequentially comparing adjacent pairs of blocks from the starting block of a file until the fragmentation point is reached. By utilizing serial analysis we are able to minimize the errors in detecting the fragmentation points. The performance results obtained from the fragmented test-sets of DFRWS 2006 and 2007 show that the method can be effectively used in recovery of fragmented files.     

Detecting file fragmentation point using sequential hypothesis testing

File carving is a technique whereby data files are extracted from a digital device without the assistance of file tables or other disk meta-data. One of the primary challenges in file carving can be found in attempting to recover files that are fragmented. In this paper, we show how detecting the point of fragmentation of a file can benefit fragmented file recovery. We then present a sequential hypothesis testing procedure to identify the fragmentation point of a file by sequentially comparing adjacent pairs of blocks from the starting block of a file until the fragmentation point is reached. By utilizing serial analysis we are able to minimize the errors in detecting the fragmentation points. The performance results obtained from the fragmented test-sets of DFRWS 2006 and 2007 show that the method can be effectively used in recovery of fragmented files.     

MEGA: A tool for Mac OS X operating system and application forensics

Computer forensic tools for Apple Mac hardware have traditionally focused on low-level file system details. Mac OS X and common applications on the Mac platform provide an abundance of information about the user's activities in configuration files, caches, and logs. We are developing MEGA, an extensible tool suite for the analysis of files on Mac OS X disk images. MEGA provides simple access to Spotlight metadata maintained by the operating system, yielding efficient file content search and exposing metadata such as digital camera make and model. It can also help investigators to assess FileVault encrypted home directories. MEGA support tools are under development to interpret files written by common Mac OS applications such as Safari, Mail, and iTunes.     

MEGA: A tool for Mac OS X operating system and application forensics

Computer forensic tools for Apple Mac hardware have traditionally focused on low-level file system details. Mac OS X and common applications on the Mac platform provide an abundance of information about the user's activities in configuration files, caches, and logs. We are developing MEGA, an extensible tool suite for the analysis of files on Mac OS X disk images. MEGA provides simple access to Spotlight metadata maintained by the operating system, yielding efficient file content search and exposing metadata such as digital camera make and model. It can also help investigators to assess FileVault encrypted home directories. MEGA support tools are under development to interpret files written by common Mac OS applications such as Safari, Mail, and iTunes.     

Distributed filesystem forensics: XtreemFS as a case study

Distributed filesystems provide a cost-effective means of storing high-volume, velocity and variety information in cloud computing, big data and other contemporary systems. These technologies have the potential to be exploited for illegal purposes, which highlights the need for digital forensic investigations. However, there have been few papers published in the area of distributed filesystem forensics. In this paper, we aim to address this gap in knowledge. Using our previously published cloud forensic framework as the underlying basis, we conduct an in-depth forensic experiment on XtreemFS, a Contrail EU-funded project, as a case study for distributed filesystem forensics. We discuss the technical and process issues regarding collection of evidential data from distributed filesystems, particularly when used in cloud computing environments. A number of digital forensic artefacts are also discussed. We then propose a process for the collection of evidential data from distributed filesystems.     

Information assurance in a distributed forensic cluster

When digital forensics started in the mid-1980s most of the software used for analysis came from writing and debugging software. Amongst these tools was the UNIX utility ‘dd’ which was used to create an image of an entire storage device. In the next decade the practice of creating and using ‘an image’ became established as a fundamental base of what we call ‘sound forensic practice’. By virtue of its structure, every file within the media was an integrated part of the image and so we were assured that it was wholesome representation of the digital crime scene. In an age of terabyte media ‘the image’ is becoming increasingly cumbersome to process, simply because of its size. One solution to this lies in the use of distributed systems. However, the data assurance inherent in a single media image file is lost when data is stored in separate files distributed across a system. In this paper we assess current assurance practices and provide some solutions to the need to have assurance within a distributed system.     

SQLite数据库结构分析在司法鉴足中的应用

SQLite是一个轻量级SQL数据库引擎,由于运行简单、功能强大,被广泛应用在手机短信、浏览器历史记录等各种应用中。在鉴定实践中也经常需要在SQLite的数据库文件中搜索查找特定内容,所以了解SQLite数据库文件结构非常重要。分析了SQLite数据库文件的结构,分析了android手机中的短信息文件的数据结构,以实际案例分析了被删除短信的搜索分析方法．这种检验分析的思路和方法对所有使用SQLite数据库的应用都是可以借鉴的。     

Study on the tracking revision history of MS Word files for forensic investigation

Document forensics remains an important field of digital forensics. To date, previously existing methods focused on the last saved version of the document file stored on the PC; however, the drawback of this approach is that this provides no indication as to how the contents have been modified. This paper provides a novel method for document forensics based on tracking the revision history of a Microsoft Word file. The proposed method concentrates on the TMP file created when the author saves the file and the ASD file created periodically by Microsoft Word during editing. A process whereby the revision history lists are generated based on metadata of the Word, TMP, and ASD files is presented. Furthermore, we describe a technique developed to link the revision history lists based on similarity. These outcomes can provide considerable assistance to a forensic investigator trying to establish the extent to which document file contents have been changed and when the file was created, modified, deleted, and copied.     

Data fragment forensics for embedded DVR systems

A recent increase in the prevalence of embedded systems has led them to become a primary target of digital forensic investigations. Embedded systems with DVR (Digital Video Recorder) capabilities are able to generate multimedia (video/audio) data, and can act as vital pieces of evidence in the field of digital forensics.To counter anti-forensics, it is necessary to derive systematic forensic techniques that can be used on data fragments in unused (unallocated) areas of files or images. Specifically, the techniques should extract meaningful information from various types of data fragments, such as non-sequential fragmentation and missing fragments overwritten by other data.This paper proposes a new digital forensic system for use on video data fragments related to DVRs. We demonstrate in detail special techniques for the classification, reassembly, and extraction of video data fragments, and introduce an integrated framework for data fragment forensics based on techniques described in this paper.