Computer forensics analyzes evidence from computers to determine details on computer incidents, similar to how CSI personnel analyze evidence from crime scenes. If you’re planning to take the Security+ exam, you should have a good understanding of forensic analysis tools used to gather and analyze computer evidence.
For example, can you answer this question?
Q. A forensic expert is preparing to analyze a hard drive. Which of the following should the expert do FIRST?
A. Capture an image.
B. Identify the order of volatility.
C. Create a chain-of-custody document.
D. Take a screenshot.
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.
Capture System Image
A forensic image of a disk captures the entire contents of the drive. Some tools use bit-by-bit copy methods that can read the data without modifying it. Other methods include hardware devices connected to the drive to write-protect it during the copy process.
Chapter 5 of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide introduced disk images as a common method used to deploy systems. These system disk images include mandatory security configurations and help ensure a system starts in a secure state. A distinct difference between standard system images and forensic images is that a forensic image is an exact copy and does not modify the original. This isn’t always true with system imaging tools.
One of the oldest disk imaging tools used for forensics is the dd command available in Unix and Linux systems, and can be installed on Windows systems. However, other tools such as EnCase and Forensic Toolkit are much easier to use so experts don’t use dd as often anymore.
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All of these methods capture the entire contents of the disk, including system files, user files, and files marked for deletion but not overwritten. Similarly, many tools include the ability to capture data within volatile memory and save it as an image.
After capturing an image, experts create a copy and analyze the copy. They do not analyze the original disk and often don’t even analyze the original image. They understand that by analyzing the contents of a disk directly, they can modify the contents. By creating and analyzing forensic copies, they never modify the original evidence.
Do You Want to Play with a Forensics Toolkit?
Kali Linux is a free Debian-based Linux distribution you can use for penetration testing and many other security tasks. If you’re taking a cybersecurity exam, you can use it to experiment with some penetration tools.
Here are three labs you can follow to install Kali Linux in a virtual environment and then run the dd command to see how it works:
Install VMware Workstation Player
Install Kali Linux within a VM
Capture Video
Video surveillance methods such as closed-circuit television (CCTV) system can be used as a detective control during an investigation. They provide reliable proof of a person’s location and activity. For example, if a person is stealing equipment or data, video may provide proof.
I remember a high school student was working nights at a local grocery store. The store had a delivery of beer in a tractor-trailer that hadn’t been unloaded yet but was kept backed up to the store loading dock overnight. The student stole several cases of beer thinking the crime was undetectable. However, the entire scene was recorded on video, and when he showed up for work the next evening, the store promptly called the police and provided a copy of the video. The video provided reliable proof that simply couldn’t be disputed.
Record Time Offset
In some cases, it’s easy to identify the time of an event such as in the following figure. In the figure, you can easily identify the exact dates and times when someone created, modified, last saved, and last accessed the file. However, in some cases you need to consider a time offset.
Windows Explorer showing exact dates and times
For example, Greenwich Mean Time (GMT) identifies the time at the Royal Observatory in Greenwich, London. Other times are based on GMT. I live in the Eastern Standard Time (EST) zone, so you can express the Date Accessed time as 5:10 p.m. EST. However, GMT uses an offset, so the same time is also 9:10 p.m. GMT. One benefit of using GMT is that it doesn’t change for daylight saving time, so it stays constant.
Many video recorders use time offsets to identify times on tape recordings rather than the actual time. For example, a recording may use a displayed counter to identify the time that has passed since the recording started. Imagine that the counter advances 1,000 ticks or counts per hour. If the counter indicates an event occurred at an offset time of 1,500 and the recording started at midnight, then the time of the event was 1:30 a.m.
When analyzing timestamps of any evidence, it’s important to understand that these times are often based on an offset. If you can’t identify the offset, you may not be able to identify the actual time.
Screenshots
Screenshots are simply pictures of what you can see displayed on a computer screen. If you want to capture exactly what a user was doing, or specific displays, a screenshot is the perfect solution.
For example, the figure shown previously, is a screenshot of Windows Explorer. You can save screenshots as graphics files and embed these graphics into documents. Many operating systems include the ability to capture the screen and save it to the Clipboard. For example, you can capture the screen of almost any system by pressing the PrtScn key found on most keyboards. Many applications such as Snagit allow you to capture screenshots from specific windows or applications, any region of the screen, and even scrolling windows such as a long web page.
Q. A forensic expert is preparing to analyze a hard drive. Which of the following should the expert do FIRST?
A. Capture an image.
B. Identify the order of volatility.
C. Create a chain-of-custody document.
D. Take a screenshot.
Answer is A. Before analyzing a hard drive, a forensic expert should capture an image of the hard drive and then analyze the image. This protects it from accidental modifications and preserves it as usable evidence.
The order of volatility identifies what data is most volatile (such as cache) and what is least volatile (such as hard drives).
A chain-of-custody document should be created when evidence is first collected.
A screenshot is taken when a system is operational.
You may also like to check out Security+ Forensic Performance Based Question here
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