Digital Forensics

Digital Forensics, Part 4: Finding Key Evidence in the Forensic Image

In the previous articles in this series, we captured an forensic image of the suspect’s hard drive, we captured a forensic image of the suspect’s RAM and we had used Autopsy to recover deleted files from our first image. In this lab, we will use Autopsy to do file analysis. In order words, we will using Autopsy to find keywords, file types, metadata, etc. that may be useful in finding evidence to support our case.

Forensic imaging, also known as disk imaging or cloning, is the process of creating an exact copy of a digital storage device for the purpose of preserving and analyzing evidence. A forensic image can be used to recover deleted files, analyze the contents of a device, and identify potential security threats. Once a forensic image has been created, the next step is to analyze it in order to find key evidence.

There are a number of tools and techniques that can be used to analyze a forensic image, including file carving, keyword searching, and metadata analysis.

File carving is the process of extracting files from a forensic image without relying on the file system. This can be useful for recovering deleted files or files that have been hidden or otherwise obscured. File carving can be done using specialized software that is designed to search for and extract specific types of files, such as image or video files.

Keyword searching is the process of searching for specific keywords or phrases within a forensic image. This can be useful for identifying relevant files or for identifying patterns of behavior. Keyword searching can be done using specialized software that is designed to search for specific keywords within a forensic image.

Metadata analysis is the process of analyzing the metadata of files within a forensic image. Metadata includes information about a file, such as when it was created, last modified, and accessed. This can be useful for identifying patterns of behavior and for determining the order in which events occurred.

Another important aspect of analyzing a forensic image is to examine the file system. Examining the file system allows the analyst to understand the structure of the image, as well as the files and folders that are present, which can provide important context for the analysis.

Finally, it is crucial to keep in mind that the process of finding key evidence in a forensic image is not only technical but also contextual. The analyst should keep in mind the context and the purpose of the investigation, and use a combination of technical and non-technical information to support the findings.

In conclusion, finding key evidence in a forensic image requires a combination of technical and contextual analysis. Tools such as file carving, keyword searching, and metadata analysis can be used to extract and analyze relevant data from a forensic image. Additionally, understanding the file system and the context of the investigation can provide important context for the analysis. It’s important to note that the process of finding key evidence in a forensic image is a complex task that requires specialized knowledge and expertise, and should be performed by qualified forensic analysts.

Step #1

Open Autopsy and navigate to our firstimage.dd.001 file.

Autopsy will immediately begin to index this image for analysis.

When it has completed its analysis, it will then categorize each file by type. As you can see in the screenshot below, Autopsy has categorized each file type including images, videos, audio, documents, executables, and deleted files.

Step #2 Search for Keywords

Let’s assume that we are looking for files that include the keyword “forensics”. We can type this word into the Search window in the upper right of our screen and click Search.

Autopsy will now commence searching every file for that keyword. As you can imagine, in a real investigation this keyword would likely be particular to the investigation such as “ransom”, “extortion”, “sex”, etc.

When Autopsy has completed its search, it will display each file that contains that keyword in the main Table window. We can then click on any of those file to examine it closer.

If we then click on the “Indexed Text” tab in the lower right window, it will show us every instance of that keyword and highlight it for us.

Step #3 Specialized Search Types

Autopsy enables us to do very specialized type searches that may be key to our investigation. These might include URL, email addresses, phone numbers or IP addresses.

Click on the eye near the upper right on this screen. It should open a pull down window like that below. Here we can search for;

1. Phone numbers

2. IP addresses

3. email addresses

4. URL’s

Let’s see if we can find any URL’s in these files that may be useful in identifying what the suspect was doing before the system was seized.

In the pull down window click on the check box next to URLs. It will populate the regex expression is using to find URL’s.

Next, click Search and Autopsy will begin looking through every file for that text pattern. The regular expression it is looking for is displayed in the right hand window.

Regular expression searches are very CPU intensive and slow, so be patient.

When it is done doing this search, it will display the results like below.

As you can see above, Autopsy displays every file that it found a URL in.

In addition, we can use this method to find email addresses as well, but when Autopsy did its initial analysis, it categorized all the email addresses it found in the Explorer pane as seen below.

 

Conclusion

Autopsy is a powerful tool for doing forensic image analysis. Among the many things it is capable of doing is deleted file analysis, file type analysis, keyword analysis, and finding such key artifacts as URL’s, email addresses, IP addresses and phone numbers. In addition, we can create custom regular expressions to search for just about any text pattern one can imagine.