Review of Digital Forensics with Open Source Tools

Monday, June 27, 2011 Posted by Corey Harrell
I became involved in the digital forensics (DF) field when I had to establish and manage a DF process to support financial investigations and fraud audits. When I got to the point of identifying tools I first looked to see what resources I had at my disposal. Lo and behold my security lab had a dongle to a commercial forensic product. In the beginning I exclusively used a few commercial products to perform forensics but over time I added additional tools to my arsenal to expand my capability. I’m bringing up my background since the intended audience for Digital Forensics with Open Source Tools (DFwOST) is new forensic practitioners and experienced DF practitioners new to open source tools. My review of DFwOST is coming from the perspective of an experienced DF practitioner who may rely on a few (or single) commercial tools during examinations.

Before diving into the world of open source tools DFwOST starts out by defining digital forensics and explaining the goals of any examination which is for an examiner to locate artifacts to indicate if a hypothesis is true or false. DFwOST then covers the three different analysis types used during an examination and the analysis types are: system, application, and file. DFwOST explains how to perform the different analysis by explaining the data, the potential artifacts of interest located in the data, and discussing the open source tools to use against the data. The system analysis covers partitioning and disk layouts of physical storage devices. In addition to this, DFwOST discusses the different file types and artifacts specific to the Windows Linux, and Mac operating systems. The application analysis explains the artifacts associated with different web browsers and mail applications. Rounding out the discussion, the file analysis covers the activities for examining the content of individual files and their metadata. The authors provided a listing of references at the end of each chapter that the reader can use to learn more about the topics DFwOST doesn't go into great detail on.

I think DFwOST will be beneficial to anyone who reads it whether if they are new to the field or an experienced practitioner. However, I think the book is a great resource to experienced DF practitioners who are not familiar with open source and free digital forensic tools. My reasoning is because DFwOST can help to expand capabilities in DF examinations, understand how commercial tools work, and identify additional tools.

Expand Capabilities in DF Examinations

Every tool has its strengths and weaknesses, and commercial tools are no different. There is not a single commercial product that has the ability examine every possible type of data or artifact encountered during exams. This issue is one of the reasons why DF practitioners have multiple tools at their disposal. How does DFwOST fit into the picture?

First DFwOST discusses tools and techniques that have a capability not present in the current crop of commercial tools. The additional capability provided by open source tools can be used to compliment the functionality of commercial tools. For example, chapter 9 discusses the timeline analysis technique and mentions a few tools to create timelines that include the metadata from the file system and various artifacts. In my experiences, timeline analysis is a powerful technique and it has helped me on a range of different examinations from financial investigations to human resource policy violation investigations to security incidents. The ability to generate timelines would be lost by solely relying on a single or few commercial products.

Understand How Commercial Tools Work

Some commercial tools automatically extract information from data and this functionality can help reduce the time needed to complete an examination. On the downside, automation provides a layer of abstraction that may result in examiners not completely understanding the data they are seeing or how the tool works. The tools (open source and free ones in Appendix A) highlighted in DFwOST can be a great educational benefit to examiners by helping better understand the data and how their commercial tools work; thus removing the layer of abstraction caused by automation. Open source tools can not only be ran against data to see how the output is different but the tools' various options can be tested and the code can be read to better understand how the tool functions. The educational benefit provided by open source tools will be helpful to any examination even if the tools are not actually used on a case.

Identify Additional Tools

DFwOST points out numerous tools to use during a digital forensic examination. Using additional tools can provide flexibility and additional resources for validation testing. At times there could be a need to only conduct a few activities and using a multipurpose commercial tool may be overkill for the task at hand. Additional time will be needed for a multipurpose tool since it takes time to load and configure the tool even if the task at hand is just to extract specific information from data. The tools in DFwOST provide this kind of flexibility.

In addition to flexibility, open source tools can be used in the validation testing of commercial tools. Does XYZ commercial software extract the information from a certain type of data properly? Does XYZ commercial tool work as advertised? Both questions can be quickly verified by reproducing the results with the open source tools discussed in DFwOST.

Five Star Review

Overall DFwOST will be a welcome addition to anyone’s DFIR library. The one topic I thought was missing from the book (or I overlooked) is mentioning the process or methods to validate digital forensic tools before they are used during an examination. I don't think the authors had to go into great detail on the subject but pointing the reader (especially people new to the field) to a few references could be helpful. Despite this, if I was posting my review on Amazon then DWwOST would get another five star rating.
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  1. Corey,

    Thanks for the review! Great job.

    Do you have any references that point to validating tools?


  2. A couple of references for understanding the process and the ways to perform validation testing.

    "SWGDE Recommended Guidelines for Validation Testing" available on the page

    The paper "Validation of Digital Forensic Tools" by P. Kanellis, E. Kiountouzis, N. Kolokotronis, & M. Drakoulis. I came across the paper in the book "Digital Crime and Forensic Science in Cyberspace" so I'm not sure if it is freely available. Here is a link to the abstract for the paper:

    The DFI News article "Validation of Forensic Tools and Software: A Quick Guide for the Digital Forensic Examiner" available at

    I found these to be good references and they helped me setup my tool validation process with supporting documentation.


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