Identifying and analyzing information security incidents and the related digital evidence is called digital forensics. Generally, forensic science is the scientific method of gathering and examining data about the past to extract useful information related to the case under investigation. Digital forensics is the analysis of digital evidence in order to answer questions related to a digital incident, which takes place at the time of the analysis in case of a live analysis or takes place in the past; this is called postmortem analysis.

Postmortem analysis is applied after the incident has occurred, and it usually takes place in all cases. However, some cases require the analysis to be conducted during the incident. Generally, the analysis can confirm or refute a hypothesis about the incident to rebuild a full picture about the activities of both the attacker and the victim during the time of the incident.

One of the definitions of digital forensics is Rodney McKemmish's, which stated the following:

From this, we can divide the digital forensics analysis into four subphases, which also represent the four principles of a successful process:

As a normal reaction, the change in technology led to a change of possible evidence, as compared to previous traditional evidence. All the components of the computer system could be evidence, such as the following:

Due to the wide range of possible evidence, the incident handler or first responder who will handle and process the available devices in the incident scene must have sufficient experience in dealing with whatever types of evidence they may find at the scene.

Handling digital devices is a very significant task, which the whole investigation process relies on. This is considered to be one of the main principal needs that have to be fulfilled in order to conduct successful digital analysis.

The main object in the digital forensic analysis is the digital device related to the security incident under investigation. The digital device was either used to commit a crime, to target an attack, or is a source of information for the analyst. The goals of the analysis phase in the digital forensics process differ from one case to another. It can be used to support or refute assumptions against individuals or entities, or it can be used to investigate information security incidents locally on the system or over a network.

Consider analyzing a compromised system, the goals of the digital forensics, as a whole, are to answer these questions:

During the analysis too, the analyst could answer some other questions based on their findings, such as the following:

During incident handling, each case can be considered as a different scenario. Therefore, different approaches can take place during the first response, based on the circumstances of the individual case. There are two general approaches that can be used to deal with a security incident:

Mainly, the hybrid approach is considered the best, where the responder conducts the live analysis on the powered on and accessible systems, records their findings, and acquires all the data, including the live ones, for postmortem analysis. Combining both results from live and postmortem analysis can clearly explain the status of the system under investigation. Performing the acquisition first in such a case is the best practice as the evidence will be acquired before any analysis traces are in the system.

In this introductory chapter, we discussed some definitions that are related to digital forensic science, its goals, and its analysis approaches.

In the next chapter, the live and postmortem analysis approaches will be explained in details with the tools that are recommended for each approach.