Computer forensics analyzes evidence from computers to determine details on computer incidents, similar to how CSI personnel analyze evidence from crime scenes. It uses a variety of different tools to gather and analyze computer evidence. If you’re planning to take the Security+ exam, you should have a basic understanding of basic forensic procedures. This includes analyzing hard drives, network traffic and logs.
For example, can you answer this question?
Q. After a recent incident, a forensic analyst was given several hard drives to analyze. What should the analyst do first?
A. Take screenshots and capture system images.
B. Take hashes and screenshots.
C. Take hashes and capture system images.
D. Perform antivirus scans and create chain-of-custody documents.
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.
Take Hashes
Hashing is an important element of forensic analysis to provide proof that collected data has retained integrity. A hash is simply a number. You can execute a hashing algorithm against data as many times as you like, and as long as the data is the same, the hash will be the same. A captured forensic image (from RAM or a disk) is just a file, and you can use hashing with forensic images to ensure image integrity.
For example, after capturing an image of a disk, an expert can create a hash of the image. The expert can then write-protect the image to prevent accidental modifications during the analysis. Later, the expert can take another hash of the image and compare it with the original hash. As long as both hashes are the same, it provides proof that the image is the same and the analysis did not modify it.
Forensic analysts sometimes make a copy of the image to analyze, instead of analyzing the first image they capture. If they ever need to verify the integrity of the copy, they run the same hashing algorithm against it. Again, as long as the hash is the same, they know the analyzed data is the same as the captured data.
Similarly, some tools allow you to create a hash of an entire drive. These verify that the imaging process has not modified data. For example, you can create a hash of a drive before capturing the image and after capturing the image. If the hashes are the same, it verifies that the imaging process did not modify the drive.
Remember this
A forensic image is a bit-by-bit copy of the data and does not modify the data during the capture. Experts capture an image of the data before analysis to preserve the original and maintain its usability as evidence. Hashing provides integrity for captured images, including images of both memory and disk drives. You can take a hash of a drive before and after capturing an image to verify that the imaging process did not modify the drive contents.
Network Traffic and Logs
A forensic investigation often includes an analysis of network traffic and available logs. This information helps the investigators re-create events leading up to and during an incident.
As an example, an organization may want to prove that a specific computer was involved in an attack. One way is to match the media access control (MAC) address used by the attacking computer with an existing computer. The MAC address is permanently assigned to a network interface card, and even though the operating system can be manipulated to use a different MAC, the actual MAC isn’t changed. In contrast, the IP address and name of the computer are not permanently assigned, and it is relatively easy to change them.
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The following figure shows a capture with an expanded packet. Data within packets identifies computers involved in a conversation based on their IP address and their MAC address. If a data capture shows a MAC address matches the actual MAC address of a suspected computer, it provides a strong indication the computer was involved in the attack.
Wireshark capture
Similarly, if the attack came from the Internet, you can trace the IP address back to the Internet Service Provider (ISP). ISPs issue IP addresses to users and the ISP logs identify exactly who was issued an IP address at any given time. For example, when David Kernell hacked into Sarah Palin’s Yahoo! email account in 2008, security experts quickly traced the attack back to him based on his IP address.
Logs record what happened during an event, when it happened, and what account was used during the event. You may remember that a Security log records logon and logoff events. Similarly, many applications require users to authenticate, and applications log authentication events. All of these logs can be invaluable in re-creating the details of an event after a security incident, including the identity of the account used in the attack.
Q. After a recent incident, a forensic analyst was given several hard drives to analyze. What should the analyst do first?
A. Take screenshots and capture system images.
B. Take hashes and screenshots.
C. Take hashes and capture system images.
D. Perform antivirus scans and create chain-of-custody documents.
Answer is C. Forensic analysts capture images and take hashes before beginning analysis, and they only analyze the image copies, not the original drive.
Screenshots are taken when a computer is running.
An antivirus scan might modify the drive and chain-of-custody documents are created when evidence is collected.
