02 May 2010
Posted in C
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Computer Forensics - refers to the science of retrieving legal evidence found inside the computer or on digital media source of some type. Computer forensics can be used to merely describe the current state of some typical piece of stored data or can be expanded to aid in the reconstruction of a series of events that may have lead up to a cyber crime for instance.
Computer forensics (sometimes known as computer forensic science) is a branch of digital forensic science pertaining to legal evidence found in computers and digital storage media. The goal of computer forensics is to examine digital media in a forensically sound manner with the aim of identifying, preserving, recovering, analyzing and presenting facts and opinions about the information.
Although it is most often associated with the investigation of a wide variety of computer crime, computer forensics may also be used in civil proceedings. The discipline involves similar techniques and principles to data recovery, but with additional guidelines and practices designed to create a legal audit trail.
Evidence from computer forensics investigations is usually subjected to the same guidelines and practices of other digital evidence. It has been used in a number of high profile cases and is becoming widely accepted as reliable within US and European court systems.
In the early 1980s personal computers became more accessible to consumers leading to their increased use in criminal activity (for example, to help commit fraud). At the same time, several new "computer crimes" were recognized (such as hacking). The discipline of computer forensics emerged during this time as a method to recover and investigate digital evidence for use in court. Today it is used to investigate a wide variety of crime, including child pornography, fraud, cyberstalking, murder and rape. The discipline also features in civil proceedings as a form of information gathering (for example, Electronic discovery)
Forensic techniques and expert knowledge are used to explain the current state of a digital artifact; such as a computer system, storage medium (e.g. hard disk or CD-ROM), an electronic document (e.g. an email message or JPEG image). The scope of a forensic analysis can vary from simple information retrieval to reconstructing a series of events. In a 2002 book Computer Forensics authors Kruse and Heiser define computer forensics as involving "the preservation, identification, extraction, documentation and interpretation of computer data". They go on to describe the discipline as "more of an art than a science", indicating that forensic methodology is backed by flexibility and extensive domain knowledge.
In court computer forensic evidence is subject to the usual requirements for digital evidence; requiring information to be authentic, reliably obtained and admissible. Different countries have specific guidelines and practices for the recovery of evidence. In the United Kingdom examiners often follow guidelines from the Association of Chief Police Officers which help ensure the authenticity and integrity of evidence. While the guidelines are voluntary they are widely accepted in courts of Wales, England and Scotland.
Computer forensics has been used as evidence in criminal law since the mid 1980s, some notable examples include:
Dennis Rader was convicted of a string of serial killings that occurred over a period of sixteen years. Towards the end of this period, Rader sent letters to the police on a floppy disk. Metadata within the documents implicated an author named "Dennis" at "Christ Lutheran Church"; this evidence helped lead to Rader's arrest.
Joseph E. Duncan III
A spreadsheet recovered from Duncan's computer contained evidence which showed him planning his crimes. Prosecutors used this to show premeditation and secure the death penalty.
Hundreds of emails on Lopatka's computer lead investigators to her killer, Robert Glass.
This case confirmed parties' duties to preserve digital evidence when litigation has commenced or is reasonably anticipated. Hard drives were analyzed by a Computer Forensics expert and could not find relevant emails which the Defendants should have. Although no evidence of deletion on the hard drives were found, evidence came out before the Court that the Defendants were found to have intentionally destroyed emails, misled and failed to disclose material facts to the Plaintiffs and the Court.
Computer forensic investigations usually follow the standard digital forensic process (acquisition, analysis and reporting). Investigations are performed on static data (i.e. acquired images) rather than "live" systems. This is a change from early forensic practices which, due to a lack of specialist tools, saw investigations commonly carried out on live data.
A number of techniques are used during computer forensics investigations.
A forensic technique that correlates information found on multiple hard drives. The process, which is still being researched, can be used for identifying social networks and for performing anomaly detection.
The examination of computers from within the operating system using custom forensics or existing sysadmin tools to extract evidence. The practice is useful when dealing with Encrypting File Systems, for example, where the encryption keys may be collected and, in some instances, the logical hard drive volume may be imaged (known as a live acquisition) before the computer is shut down.
A common technique used in computer forensics is the recovery of deleted files. Modern forensic software have their own tools for recovering or carving out deleted data. Most operating systems and file systems do not always erase physical file data, allowing it to be reconstructed from the physical disk sectors. File carving involves searching for known file headers within the disk image and reconstructing deleted materials.
When seizing evidence, if the machine is still active, any information stored solely in RAM that is not recovered before powering down may be lost. One application of "live analysis" is to recover RAM data (for example, using Microsoft's COFEE tool) prior to removing an exhibit.
RAM can be analyzed for prior content after power loss, because the electrical charge stored in the memory cells takes time to dissipate. The length of time for which data recovery is possible is increased by low temperatures and higher cell voltages. Holding unpowered RAM below −60 °C will help preserve the residual data by an order of magnitude, thus improving the chances of successful recovery. However, it can be impractical to do this during a field examination.
A number of open source and commercial tools exist for computer forensics investigation. Typical forensic analysis includes a manual review of material on the media, reviewing the Windows registry for suspect information, discovering and cracking passwords, keyword searches for topics related to the crime, and extracting e-mail and pictures for review.