1 COMPUTER FORENSICS Introduction 2 Computers have permeated society and are used in countless ways with innumerable applications. Similarly, the role of electronic data in investigative work has realized exponential growth in the last decade. The usage of computers and other electronic data storage devices leaves the footprints and data trails of their users. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Introduction 3 Computer forensics involves the preservation, acquisition, extraction, and interpretation of computer data. In today’s world of technology, many devices are capable of storing data and could thus be grouped into the field of computer forensics. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- The Basics 4 Before getting into the nuts and bolts of computers, the important distinction between hardware and software must be established. Hardware comprises the physical and tangible components of the computer. Software conversely, is a set of instructions compiled into a program that performs a particular task. Software are those programs and applications that carry out a set of instructions on the hardware. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Terminology 5 Computer Case/Chassis: This is the physical box holding the fixed internal computer components in place. Power Supply: PC’s power supply converts the power it gets from the wall outlet to a useable format for the computer and its components. Motherboard: The main circuit board contained within a computer (or other electronic devices) is referred to as the motherboard. System Bus: Contained on the motherboard, the system bus is a vast complex network of wires that serves to carry data from one hardware device to another. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Terminology 6 Read Only Memory (ROM): ROM chips store programs called firmware, used to start the boot process and configure a computer’s components. Random Access Memory (RAM): RAM serves to take the burden off of the computer’s processor and Hard Disk Drive (HDD). The computer, aware that it may need certain data at a moments notice, stores the data in RAM. RAM is referred to as volatile memory because it is not permanent; its contents undergo constant change and are forever lost once power is taken away from the computer. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Terminology 7 Central Processing Unit (CPU): The CPU, also referred to as a processor, is essentially the brains of the computer. Input Devices: These devices are used to get data into the computer To name a few: Keyboard Mouse Joy stick Scanner Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Terminology 8 Output Devices: Equipment through which data is obtained from the computer. To name a few: Monitor Printer Speakers The Hard Disk Drive (HDD) is typically the primary location of data storage within the computer. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Terminology 9 Different operating systems map out (partition) HDDs in different manners Examiners must be familiar with the file system they are examining. Evidence exists in many different locations and in numerous forms on a HDD. The type of evidence can be grouped under two major sub-headings: visible and latent data. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- How Data is Stored 10 Generally speaking a HDD needs to have its space defined before it is ready for use. Partitioning the HDD is the first step. When partitioned, HDDs are mapped (formatted) and have a defined layout. They are logically divided into sectors, clusters, tracks, and cylinders. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- How Data is Stored 11 Sectors are typically 512 bytes in size. Remember a byte is 8 bits . A bit is a single 1 or 0. Clusters are groups of sectors and their size is defined by the operating system. Clusters are always in sector multiples of two. A cluster, therefore, will consist of 2, 4, 6, 8, or etc. sectors. (With modern day operating systems, the user can exercise some control over the amount of sectors per cluster.) Tracks are concentric circles that are defined around the platter. Cylinders are groups of tracks that reside directly above and below each other. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- How Data is Stored 12 After the partitioning and formatting processes are complete, the HDD will have a map of the layout of the defined space in that partition. Partitions utilize a File Allocation Table “FAT” to keep track of the location of files and folders (data) on the HDD. While the NTFS partition (most current Window systems-2000 and XP) utilizes, among other things, a Master File Table (MFT). Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- How Data is Stored 13 Each partition table (map) tracks data in different ways. The computer forensic examiners should be versed in the technical nuances of the HDDs they examine. It is sufficient for purposes here, however, to merely visualize the partition table as a map to where the data is located. This map uses the numbering sectors, clusters, tracks, and cylinders to keep track of the data. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Processing the Electronic CS 14 Processing the electronic crime scene has a lot in common with processing a traditional crime scene. Warrants Documentation Good investigation techniques At this point, a decision must be made as to whether a live acquisition of the data is necessary. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Shutdown vs. Pulling the Plug 15 Several factors influence the systematic shutdown vs. pulling the plug decision. For example, if encryption is being used and pulling the plug will encrypt the data rendering it unreadable without a password or key, therefore pulling the plug would not be prudent. Similarly, if crucial evidentiary data exists in RAM and has not been saved to the HDD and will thus be lost with discontinuation of power to the system, another option must be considered. Regardless, the equipment will most likely be seized. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Forensic Image Acquisition 16 Now that the items have been seized, the data needs to be obtained for analysis. The computer Hard Disk Drive will be used as an example, but the same “best practices” principals apply for other electronic devices as well. Throughout the entire process, the computer forensic examiner must adopt the method that is least intrusive. The goal with obtaining data from a HDD is to do so with out altering even one bit of data. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Forensic Image Acquisition 17 Because booting a HDD to its operating system changes many files and could potentially destroy evidentiary data, obtaining data is generally accomplished by removing the HDD from the system and placing it in a laboratory forensic computer so that a forensic image can be created. Occasionally, in cases of specialized or unique equipment or systems the image of the HDD must be obtained utilizing the seized computer. Regardless, the examiner needs to be able to prove that the forensic image he/she obtained includes every bit of data and caused no changes (writes) to the HDD. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Computer Fingerprint 18 To this end, a sort of fingerprint of the drive is taken before and after imaging. This fingerprint is accomplished through the use of a Message Digest 5 (MD5), Secure Hash Algorithm (SHA), or similar validated algorithm. Before imaging the drive the algorithm is run and a 32 character alphanumeric string is produced based on the drive’s contents. It then run against the resulting forensic image and if nothing changed the same alphanumeric string will be produced, thus demonstrating that the image is all-inclusive of the original contents and that nothing was altered in the process. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Visible Data 19 Visible data is that data which the operating system is aware of. Consequently this data is easily accessible to the user. From an evidentiary standpoint, it can encompass any type of user created data like: Word processing documents Spread sheets Accounting records Databases Pictures Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Temporary Files and Swap Space 20 Temporary files, created by programs as a sort of “back-up on the fly” can also prove valuable as evidence. Finally, data in the swap space (utilized to conserve the valuable RAM within the computer system) can yield evidentiary data. Latent data, on the other hand, is that data which the operating system is not aware of. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Latent Data 21 Evidentiary latent data can exist in both RAM and file slack. RAM slack is the area from the end of the logical file to the end of the sector. File slack is the remaining area from the end of the final sector containing data to the end of the cluster. Another area where latent data might be found is in unallocated space. Unallocated space is that space on a HDD the operating system sees as empty and ready for data. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Latent Data 22 The constant shuffling of data through deletion, defragmentation, swapping, etc., is one of the ways data is orphaned in latent areas. Finally, when a user deletes files the data typically remains behind. Deleted files are therefore another source of latent data to be examined during forensic analysis. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Knowledge and Skill 23 Computer file systems and data structures are vast and complex. Therefore, areas of forensic analysis are almost limitless and constrained only by the knowledge and skill of the examiner. With a working knowledge of a computer’s function, how they are utilized, and how they store data, an examiner is on his or her way to begin to locate the evidentiary data. Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Review Questions 1-12 24 Describe the difference between software and media and give two examples of each What is the motherboard and why is it central to the functioning of a computer? Define RAM and ROM and explain the difference between the two. Define the terms input device and output device and name three examples of each/ What is the most common storage device on most computers? Name three other types of storage devices. What type of hardware device do personal computers typically use to communicate with one another? Name two ways this device can send and receive data. What is the role of the operating system in a computer? Name three common operating systems. Name and describe the two processes that must be performed on a hard disk drive (HDD) before it is ready for use. What is a FAT and what is its purpose? What is the forensic examiner’s main goal when obtaining data from an HDD? Why is this best accomplished by removing the HDD from the system and placing it in a laboratory forensic computer? Why does a forensic examiner take a “fingerprint ” of a drive before and after imaging its contents? What is a swap file and how is it useful for forensic examiners? Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Review Questions 13-17 25 What is the difference between visible and latent data? How is latent data viewed? What is file slack? How can it be useful to the forensic examiner? What is unallocated space? Name three processes that cause latent data to be stored in unallocated space. What is an Internet cache and why is it of interest to forensic examiners? What are cookies? What is their basic purpose and how are they used by forensic examiners? Criminalistics, 10e Richard Saferstein © 2011, 2007, 2004, 2001, 1998, 1995 Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved. 19- Figure 19–3 Partitions of a hard disk drive. 26 Figure 19–7 As user switches between applications and performs multiple tasks, data is swapped back and forth between RAM and the computer’s hard drive. This area on the hard drive is referred to as either swap space or a paging file. 27 Figure 19–8 Slack space illustrated in a two-sector cluster. Cluster sizes are typically greater than two sectors, but two sectors are displayed here for simplicity. 28 Figure 19–9 File slack. 29