Imaging Hard Drives
The data recovery team has been busy making disk images for the last couple of weeks and working with a variety of unique tools. The objective of our team is to test and determine the effective means of securely deleting data. Our investigation requires a set of samples to test our techniques and programs. The creation of disk images allows us to safely do this and inspect the data without risk. How clean can a hard drive be and what do these standards look like?
What is a Disk Image?
In a world where 95% of people own a smartphone and 85% have a computer, disk images are the norm for digital forensics and criminal justice as a whole. A disk image is a collection of the data that’s stored on a device. Programs can load these files, to display the contains of the original source material. Some of these programs include GetDataBack and Wizard Partition Recovery. Sleuth Kits like FTK Imager can often produce disk images as well.
(From left to right) GetDataBack and Wizard Partition Recovery
Why Use Disk Images?
The most important piece of a case is the evidence that will solve it. The rise of technology has made computers the easiest way to store and send data. Thus, the evidence is mostly localized to a drive and its safety becomes of the utmost importance. Data recovered from a crime scene is volatile and extremely sensitive. Investigators cannot go into the device haphazardly or they run the risk of altering critical data. Altered data is unusable in court, thus data integrity and movement are heavily documented and preserved. However, in conjunction with other investigative devices, disk images allow users to access the data without risk of invalidating the evidence. They also allow an investigator to look through the data without the physical components, allowing easy access and transportation. Not only can disk images come from computers and hard drives, but also from phones and tablets.
The downside to disk images is that files are often quite large, but this depends on the size of the storage device they were made from. Compression usually mitigates this problem, but frequently, the disk images will keep the exact same size as the device being copied. This presents more problems, such as the amount of time it takes to create the file. The means of transportation also pose a problem unless there is another hard drive or cloud storage that is the same size or larger.
Benefits of File Hashing
Every detail of digital evidence is unique and valuable to digital forensic analysts and the law. Even an edit as small as changing a character then changing it back could make the data unusable in court. This is due to the creation of hash files and how they ensure validity. File hashing is the process of creating a code for a file that’s linked to the file itself. If any changes happen, including the opening, copying, pasting, or moving of a file, the hash value will change. This ensures the integrity of the evidence, even if there is no way someone could tell that a change had been made. This code is one way generated, meaning nothing can glean data from the code. Standalone programs found on the internet can generate this code. Integrating file hashing it into programs can generate this code while also completing some other function.
(From left to right) The program File Hasher in standby and File Hasher in progress
The program above is an example of a file hasher, aptly called “file hasher”. It takes the file from the user then generates a code based on the size and order of the characters in the file. This is how it ensures that there have been absolutely no changes to the order of the code. These changes can occur even when moving or copying the image.
The method of creating this code is not universal, and there are many types and methods of hash algorithms. The most popular are MD5 and SHA1, which generate a 40 digit long code. Other types of hash algorithms include RIPEMD, Whirlpool, and Blake, which all vary in the length of the code as well as the structure of the output. Though SHA1 is no longer considered safe for government use, it is still a very effective and safe method to ensure the safety of noncritical data.
As previously mentioned, the hash code changes for all interactions with it. That of course raises the question: How do you copy the data from the device without changing the hash code? The answer is a device called a write blocker, which allows the user to move or copy evidence from a hard drive onto a computer without changing the data. It does this by blocking commands from the computer that attempt to change the data on the device. This preserves integrity for the investigators and allows them to create the hard drive image. This only lets the user read and move the files. Write blockers do not prevent changes in computer data, though. This means data intentionally or unintentionally changed on the computer is still not viable.
Data recovery is the future of criminal justice and the better understanding we have of the technology used, the easier it is to understand what does and does not work. Data recovery programs allow easy access to data and allow the performance of digital investigations without a hitch. Write blockers may not always be a professional tool with limited public access. We believe the future will be more accustomed to these practices, making data easier and safer to store. To stay updated with the conclusion of our project, check out our Twitter, Instagram, and Facebook!