Digital Forensic Science

Digital forensics

Digital forensics (sometimes known as digital forensic science) is a branch of forensic science encompassing the recovery and investigation of material found in digital devices, often in relation to computer crime.[1][2] The term digital forensics was originally used as a synonym for computer forensics but has expanded to cover investigation of all devices capable of storing digital data.

Digital forensics investigations have a variety of applications. The most common is to support or refute a hypothesis before criminal or civil (as part of the electronic discovery process) courts. Forensics may also feature in the private sector; such as during internal corporate investigations or intrusion investigation (a specialist probe into the nature and extent of an unauthorized network intrusion).

The technical aspect of an investigation is divided into several sub-branches, relating to the type of digital devices involved; computer forensics, network forensics, forensic data analysis and mobile device forensics. The typical forensic process encompasses the seizure, forensic imaging (acquisition) and analysis of digital media and the production of a report into collected evidence.

As well as identifying direct evidence of a crime, digital forensics can be used to attribute evidence to specific suspects, confirm alibis or statements, determine intent, identify sources (for example, in copyright cases), or authenticate documents. Investigations are much broader in scope than other areas of forensic analysis (where the usual aim is to provide answers to a series of simpler questions) often involving complex time-lines or hypotheses.

A digital forensic investigation commonly consists of 3 stages: acquisition or imaging of exhibits,[23] analysis, and reporting.[6][24] Ideally acquisition involves capturing an image of the computer's volatile memory (RAM) and creating an exact sector level duplicate (or "forensic duplicate") of the media, often using a write blocking device to prevent modification of the original. However, the growth in size of storage media and developments such as cloud computing [26] have led to more use of 'live' acquisitions whereby a 'logical' copy of the data is acquired rather than a complete image of the physical storage device.[23] Both acquired image (or logical copy) and original media/data are hashed (using an algorithm such as SHA-1 or MD5) and the values compared to verify the copy is accurate.

Application

An example of an image's Exif metadata that might be used to prove its origin

Digital forensics is commonly used in both criminal law and private investigation. Traditionally it has been associated with criminal law, where evidence is collected to support or oppose a hypothesis before the courts. As with other areas of forensics this is often as part of a wider investigation spanning a number of disciplines. In some cases the collected evidence is used as a form of intelligence gathering, used for other purposes than court proceedings (for example to locate, identify or halt other crimes). As a result, intelligence gathering is sometimes held to a less strict forensic standard.

In civil litigation or corporate matters digital forensics forms part of the electronic discovery (or eDiscovery) process. Forensic procedures are similar to those used in criminal investigations, often with different legal requirements and limitations. Outside of the courts digital forensics can form a part of internal corporate investigations.

A common example might be following unauthorized network intrusion. A specialist forensic examination into the nature and extent of the attack is performed as a damage limitation exercise. Both to establish the extent of any intrusion and in an attempt to identify the attacker. Such attacks were commonly conducted over phone lines during the 1980s, but in the modern era are usually propagated over the Internet.

The main focus of digital forensics investigations is to recover objective evidence of a criminal activity (termed actus reus in legal parlance). However, the diverse range of data held in digital devices can help with other areas of inquiry.

Attribution

Meta data and other logs can be used to attribute actions to an individual. For example, personal documents on a computer drive might identify its owner.

Alibis and statements

Information provided by those involved can be cross checked with digital evidence. For example, during the investigation into the Soham murders the offender's alibi was disproved when mobile phone records of the person he claimed to be with showed she was out of town at the time.

Intent

As well as finding objective evidence of a crime being committed, investigations can also be used to prove the intent (known by the legal term mens rea). For example, the Internet history of convicted killer Neil Entwistle included references to a site discussing How to kill people.

Evaluation of source

File artifacts and meta-data can be used to identify the origin of a particular piece of data; for example, older versions of Microsoft Word embedded a Global Unique Identifer into files which identified the computer it had been created on. Proving whether a file was produced on the digital device being examined or obtained from elsewhere (e.g., the Internet) can be very important.

Document authentication

Related to "Evaluation of source," meta data associated with digital documents can be easily modified (for example, by changing the computer clock you can affect the creation date of a file). Document authentication relates to detecting and identifying falsification of such details.

Branches

Digital forensics investigation is not restricted to retrieve data merely from the computer, as laws are breached by the criminals and small digital devices (e.g. tablets, smartphones, flash drives) are now extensively used. Some of these devices have volatile memory while some have non-volatile memory. Sufficient methodologies are available to retrieve data from volatile memory, however, there is lack of detailed methodology or a framework for data retrieval from non-volatile memory sources.[37] Depending on the type of devices, media or artifacts, digital forensics investigation is branched into various types.

Computer forensics

Main article: Computer forensics

The goal of computer forensics is to explain the current state of a digital artifact; such as a computer system, storage medium or electronic document. The discipline usually covers computers, embedded systems (digital devices with rudimentary computing power and onboard memory) and static memory (such as USB pen drives).

Computer forensics can deal with a broad range of information; from logs (such as internet history) through to the actual files on the drive. In 2007 prosecutors used a spreadsheet recovered from the computer of Joseph E. Duncan III to show premeditation and secure the death penalty. Sharon Lopatka's killer was identified in 2006 after email messages from him detailing torture and death fantasies were found on her computer.

cell phone in bag
Fig.1. - Mobile phones in a Evidence bag
cell phone in bag
Fig.2. - Private Investigator & Certified Digital Forensics Examiner Imaging a hard drive in the field for forensic examination.

Mobile device forensics

Main article: Mobile device forensics

Mobile device forensics is a sub-branch of digital forensics relating to recovery of digital evidence or data from a mobile device. It differs from Computer forensics in that a mobile device will have an inbuilt communication system (e.g. GSM) and, usually, proprietary storage mechanisms. Investigations usually focus on simple data such as call data and communications (SMS/Email) rather than in-depth recovery of deleted data. SMS data from a mobile device investigation helped to exonerate Patrick Lumumba in the murder of Meredith

Mobile devices are also useful for providing location information; either from inbuilt gps/location tracking or via cell site logs, which track the devices within their range. Such information was used to track down the kidnappers of Thomas Onofri in 2006.

Network forensics

Main article: Network forensics

Network forensics is concerned with the monitoring and analysis of computer network traffic, both local and WAN/internet, for the purposes of information gathering, evidence collection, or intrusion detection. Traffic is usually intercepted at the packet level, and either stored for later analysis or filtered in real-time. Unlike other areas of digital forensics network data is often volatile and rarely logged, making the discipline often reactionary.

In 2000 the FBI lured computer hackers Aleksey Ivanov and Gorshkov to the United States for a fake job interview. By monitoring network traffic from the pair's computers, the FBI identified passwords allowing them to collect evidence directly from Russian-based computers.

Forensic data analysis

Main article: Forensic data analysis

Forensic Data Analysis is a branch of digital forensics. It examines structured data with the aim to discover and analyse patterns of fraudulent activities resulting from financial crime.

Database forensics

Main article: Database forensics

Database forensics is a branch of digital forensics relating to the forensic study of databases and their metadata. Investigations use database contents, log files and in-RAM data to build a timeline or recover relevant information.

cell phone in bag