2. Objectives
• Explain the purpose and structure of file systems
• Describe Microsoft file structures
• Explain the structure of New Technology File
System (NTFS) disks
• List some options for decrypting drives encrypted
with whole disk encryption
3. Objectives (continued)
• Explain how the Windows Registry works
• Describe Microsoft startup tasks
• Describe MS-DOS startup tasks
• Explain the purpose of a virtual machine
5. Understanding File Systems
• File system-controls how data is stored and retrieved.
• Without a file system, data placed in a storage medium
would be one large body of data with no way to tell where
one piece of data stops and the next begins.
• Type of file system an OS uses determines how data is
stored on the disk
• A file system is usually directly related to an OS
• When you need to access a suspect’s computer to
acquire or inspect data
– You should be familiar with the computer’s platform.
6. Understanding the Boot Sequence
• Complementary Metal Oxide Semiconductor
(CMOS)
– Computer stores system configuration and date and
time information in the CMOS
• When power to the system is off
• Basic Input/Output System (BIOS)
– Contains programs that perform input and output at
the hardware level
7. Understanding the Boot Sequence
(continued)
• Bootstrap process
– start up process that takes place when you start up a computer.
When you turn on or restart a computer, it automatically loads a
sequence of commands that initializes the system, checks for
hardware and loads the operating system.
– Contained in ROM, tells the computer how to proceed
– Displays the key or keys you press to open the CMOS setup
screen
• Could be Delete, F2, F10, Ctrl+Alt+Insert, Ctrl+A, Ctrl+S, Ctrl+F1,
or something else
• CMOS should be modified to boot from a forensic floppy disk
or CD
9. Understanding Disk Drives
• Disk drives are made up of one or more platters
coated with magnetic material.
• Disk drive components
– Geometry
– Head
– Tracks
– Cylinders
– Sectors
• Holds 512 bytes, you cannot read or write anything
less than a sector
12. Understanding Disk Drives (continued)
• Properties handled at the drive’s hardware or firmware level
– Zoned bit recording (ZBR)- method of increasing available hard
drive by increasing the amount of sectors per track.
– Track density-tracks are concentric circles around the disk.
– Areal density-It is a measurement of the amount of data that can
be stored on a given unit of physical space on storage media.
– Head and cylinder skew
13. – The offset distance from the start of the last track of the
previous cylinder so that the head has time to seek from
cylinder to cylinder and be at the start of the first track of the
new cylinder.
– The offset distance from the start of the previous track so that
the head has time to switch from top of platter to bottom of
platter and be at the start of the new track
17. Exploring Microsoft File Structures
• In Microsoft file structures, sectors are grouped to
form clusters
– Storage allocation units of one or more sectors
• Clusters are typically 512, 1024, 2048, 4096, or
more bytes each
• Combining sectors minimizes the overhead of
writing or .reading files to a disk.
18. Exploring Microsoft File Structures
(continued)
• Clusters are numbered sequentially starting at 2
– First sector of all disks contains a system area, the
boot record, and a file structure database
• OS assigns these cluster numbers, called logical
addresses
• Sector numbers are called physical addresses
• Clusters and their addresses are specific to a
logical disk drive, which is a disk partition
19. Disk Partitions
• A partition is a logical drive
• FAT16(File Allocation Table) does not recognize disks larger than 2 GB
– Large disks have to be partitioned
• Partition gap
– Unused space between partitions
– The relationship between capacities of sector and cluster in FAT 16 are
following:
Capacity of sector Capacity of cluster
16MB-127MB 2KB
128MB-255MB 4KB
256MB-511MB 8KB
512MB-1023MB 16KB
1024MB-2047MB 32KB
20. Disk Partitions (continued)
• Disk editor utility can alter information in partition
table
– To hide a partition
• Can examine a partition’s physical level with a disk
editor:
– HxD, Norton DiskEdit, WinHex, or Hex Workshop
• Analyze the key hexadecimal codes the OS uses to
identify and maintain the file system.
21. Demo: VM with Three Partitions
• Virtual Machine(VM):creating a computer within a
computer.Each virtual machine provides its own
virtual hardware, including CPUs, memory, hard
drives, network interfaces and other devices.
• Partition Types
– NTFS: 07
– FAT: 06
– FAT32: 0B
22. Viewing the Partition Table HxD
• Start HxD, Extras, Open Disk, choose Physical
Disk
• Partition Table starts at 0x1BE
• Partition Type field is at offset 0x04 in each record
23. Master Boot Record(MBR) Structure
• MBR is a structure
that holds the boot
loader program and
the partition table.
The MBR is always
located at the very
start of the disk.
• The length of the
MBR structure is
512 bytes.
24. Partition Table Structure
• The partition table is
64 bytes long and is
located inside the
MBR at sector
0x1BE.
• The partition table is
an array of 4
partition table
entries each of 16
bytes thus: 16x4 =
64.
26. Partition Mark at Start of Volume
• Start HxD, Extras, Open Disk
• NTFS
• FAT32
27. BMP File in HxD
• Start HxD, File, Open
• BM at start indicates a BMP(Bit Map File) file
28. Word Doc File in HxD
• Start HxD, File, Open
• Word 2003 Format uses these 7 bytes
• .docx format is actually a Zip archive
29. Master Boot Record
• On Windows and DOS computer systems
– Boot disk contains a file called the Master Boot
Record (MBR)
• MBR stores information about partitions on a disk
and their locations, size, and other important items
• Several software products can modify the MBR,
such as PartitionMagic’s Boot Magic
30. Examining FAT Disks
• File Allocation Table (FAT)
– File structure database that Microsoft originally
designed for floppy disks
– Used before Windows NT and 2000
• FAT database is typically written to a disk’s
outermost track and contains:
– Filenames, directory names, date and time stamps,
the starting cluster number, and file attributes
• FAT versions
– FAT12, FAT16, FAT32, FATX (for Xbox), and VFAT
31. FAT Versions
• FAT12—for floppy disks, max size 16 MB
• FAT16—allows hard disk sizes up to 2 GB
• FAT32— allows hard disk sizes up to 2 TB
• FATX—For Xbox media
– The date stamps start at the year 2000, unlike the other FAT
formats that start at 1980
• VFAT (Virtual File Allocation Table)
– Allows long file names on Windows (MS-DOS had 8.3
limitation)
32. Examining FAT Disks (continued)
• Cluster sizes vary according to the hard disk size
and file system
• This table is for FAT-16
33. Examining FAT Disks (continued)
• Microsoft OSs allocate disk space for files by
clusters
– Results in drive slack
• Unused space in a cluster between the end of an
active file and the end of the cluster
• Drive slack includes:
– RAM slack and file slack
• An unintentional side effect of FAT16 having large
clusters was that it reduced fragmentation
– As cluster size increased
34. Examining FAT Disks (continued)
RAM Slack is defined as the slack space in the last written sector of a
file, while file slack is defined as the unwritten sectors left in a cluster.
35. Examining FAT Disks (continued)
• When you run out of room for an allocated cluster
– OS allocates another cluster for your file, which
creates more slack space on the disk
• As files grow and require more disk space,
assigned clusters are chained together
– The chain can be broken or fragmented
37. Examining FAT Disks (continued)
• When the OS stores data in a FAT file system, it
assigns a starting cluster position to a file
– Data for the file is written to the first sector of the first
assigned cluster
• When this first assigned cluster is filled and runs out
of room
– FAT assigns the next available cluster to the file
• If the next available cluster isn’t contiguous to the
current cluster
– File becomes fragmented
38. Deleting FAT Files
• In Microsoft OSs, when a file is deleted
– Directory entry is marked as a deleted file
• With the HEX E5 (σ) character replacing the first letter
of the filename
• FAT chain for that file is set to 0
• Data in the file remains on the disk drive
• Area of the disk where the deleted file resides
becomes unallocated disk space
– Available to receive new data from newly created
files or other files needing more space
39. Examining NTFS Disks
• New Technology File System (NTFS)
– Introduced with Windows NT
– Recommended file system for Windows 200 Pro,
XP, and later versions through Windows 7 at least
• Improvements over FAT file systems
– NTFS provides more information about a file
– NTFS gives more control over files and folders
40. Examining NTFS Disks (continued)
• In NTFS, everything written to the disk is
considered a file
• On an NTFS disk
– First data set is the Partition Boot Sector
– Next is Master File Table (MFT)
• NTFS results in much less file slack space
• Clusters are smaller for smaller disk drives
• NTFS also uses Unicode
– An international data format
42. NTFS File System
• MFT(master file table) contains information about
all files on the disk
– Including the system files the OS uses
• In the MFT, the first 15 records are reserved for
system files
• Records in the MFT are called metadata
45. MFT and File Attributes
• In the NTFS MFT
– All files and folders are stored in separate records of
1024 bytes each
• Each record contains file or folder information
– This information is divided into record fields containing
metadata
• A record field is referred to as an attribute ID
• File or folder information is typically stored in one of
two ways in an MFT record:
– Resident and nonresident
46. MFT and File Attributes (continued)
• Files larger than 512 bytes are stored outside the
MFT
– MFT record provides cluster addresses where the
file is stored on the drive’s partition
• Referred to as data runs
• Each MFT record starts with a header identifying it
as a resident or nonresident attribute
52. Understanding Whole Disk Encryption
• In recent years, there has been more concern
about loss of
– Personal identity information (PII) and trade
secrets caused by computer theft
• Of particular concern is the theft of laptop
computers and other handheld devices
• To help prevent loss of information, software
vendors now provide whole disk encryption
53. Understanding Whole Disk Encryption
(continued)
• Current whole disk encryption tools offer the
following features:
– Preboot authentication(extn of BIOS)
– Full or partial disk encryption with secure hibernation
– Advanced encryption algorithms
– Key management function
– A Trusted Platform Module (TPM) microchip to
generate encryption keys and authenticate logins
54. Understanding Whole Disk Encryption
(continued)
• Whole disk encryption tools encrypt each sector of
a drive separately
• Many of these tools encrypt the drive’s boot sector
– To prevent any efforts to bypass the secured drive’s
partition
• To examine an encrypted drive, decrypt it first
– Run a vendor-specific program to decrypt the drive
55. Examining Microsoft BitLocker
• Available only with Vista/Win 7 Enterprise and Ultimate
editions
• Hardware and software requirements
– A computer capable of running Windows Vista/7
– The TPM microchip, version 1.2 or newer
– A computer BIOS compliant with Trusted Computing
Group (TCG)
– Two NTFS partitions; a 1.5 GB or 100 MB partition use
just for BitLocker, and the partition containing Windows
– The BIOS configured so that the hard drive boots first
before checking other bootable peripherals
56. Examining Third-Party Disk Encryption
Tools
• Some available third-party WDE(whole disk encryption)
utilities:
– PGP (Pretty Good Privacy )Whole Disk Encryption
– Voltage SecureDisk
– Utimaco SafeGuard Easy
– Jetico BestCrypt Volume Encryption
– SoftWinter Sentry 2020 for Windows XP
• Some available open-source encryption tools:
– TrueCrypt
– CrossCrypt
– FreeOTFE
58. Understanding the Windows Registry
• Registry
– A database that stores hardware and software
configuration information, network connections, user
preferences, and setup information
• For investigative purposes, the Registry can
contain valuable evidence
• To view the Registry, you can use:
– Regedit (Registry Editor) program for Windows 9x
systems
– Regedt32 for Windows 2000 and XP
59. Exploring the Organization of the
Windows Registry
• Registry terminology:
– Registry
– Registry Editor
– HKEY
– Key
– Subkey
– Branch
– Value
– Default value
– Hives
63. Understanding Microsoft Startup
Tasks
• Learn what files are accessed when Windows
starts
• This information helps you determine when a
suspect’s computer was last accessed
– Important with computers that might have been used
after an incident was reported
64. Startup in Windows NT and Later
• All Windows NT computers perform the following
steps when the computer is turned on:
– Power-on self test (POST)
– Initial startup
– Boot loader
– Hardware detection and configuration
– Kernel loading
– User logon
65. Startup Process for Windows Vista
• Uses the new Extensible Firmware Interface ( EFI)
as well as the older BIOS system.
• NT Loader (NTLDR) has been replaced by three
boot utilities
– Bootmgr.exe—displays list of operating systems
– Winload.exe—loads kernel, HAL, and drivers
– Winresume.exe—restarts Vista after hibernation
66. Startup Files for Windows XP
• NT Loader (NTLDR)
• Boot.ini
• BootSect.dos
• NTDetect.com
• NTBootdd.sys
• Ntoskrnl.exe
• Hal.dll
• Pagefile.sys
• Device drivers
68. Startup in Windows NT and Later
(continued)
• Contamination Concerns with Windows XP
– When you start a Windows XP NTFS workstation,
several files are accessed immediately
• The last access date and time stamp for the files
change to the current date and time
– Destroys any potential evidence
• That shows when a Windows XP workstation was last
used
69. Startup in Windows 9x/Me
• System files in Windows 9x/Me containing valuable
information can be altered easily during startup
• Windows 9x and Windows Me have similar boot
processes
– With Windows Me you can’t boot to a true MS-DOS
mode
• Windows 9x OSs have two modes:
– DOS protected-mode interface (DPMI)
– Protected-mode GUI
70. Startup in Windows 9x/Me (continued)
• The system files used by Windows 9x have their
origin in MS-DOS 6.22
– Io.sys communicates between a computer’s BIOS,
the hardware, and the OS kernel
• If F8 is pressed during startup, Io.sys loads the
Windows Startup menu
– Msdos.sys is a hidden text file containing startup
options for Windows 9x
– Command.com provides a command prompt when
booting to MS-DOS mode (DPMI)
72. Understanding MS-DOS Startup Tasks
• Two files are used to configure MS-DOS at startup:
– Config.sys
• A text file containing commands that typically run only
at system startup to enhance the computer’s DOS
configuration
– Autoexec.bat
• A batch file containing customized settings for MS-
DOS that runs automatically
• Io.sys is the first file loaded after the ROM
bootstrap loader finds the disk drive
73. Understanding MS-DOS Startup Tasks
(continued)
• Msdos.sys is the second program to load into RAM
immediately after Io.sys
– It looks for the Config.sys file to configure device
drivers and other settings
• Msdos.sys then loads Command.com
• As the loading of Command.com nears completion,
Msdos.sys looks for and loads Autoexec.bat
74. Other Disk Operating Systems
• Control Program for Microprocessors (CP/M)
– First nonspecific microcomputer OS
– Created by Digital Research in 1970
– 8-inch floppy drives; no support for hard drives
• Digital Research Disk Operating System (DR-DOS)
– Developed in 1988 to compete with MS-DOS
– Used FAT12 and FAT16 and had a richer command
environment
75. Other Disk Operating Systems
(continued)
• Personal Computer Disk Operating System (PC-
DOS)
– Created by Microsoft under contract for IBM
– PC-DOS works much like MS-DOS
77. Understanding Virtual Machines
• Virtual machine
– Allows you to create a representation of another
computer on an existing physical computer
• A virtual machine is just a few files on your hard
drive
– Must allocate space to it
• A virtual machine recognizes components of the
physical machine it’s loaded on
– Virtual OS is limited by the physical machine’s OS
79. Understanding Virtual Machines
(continued)
• In computer forensics
– Virtual machines make it possible to restore a
suspect drive on your virtual machine
• And run nonstandard software the suspect might have
loaded
• From a network forensics standpoint, you need to
be aware of some potential issues, such as:
– A virtual machine used to attack another system or
network
80. Creating a Virtual Machine
• Two popular applications for creating virtual
machines
– VMware and Microsoft Virtual PC
• Using Virtual PC
– You must download and install Virtual PC first
83. Creating a Virtual Machine (continued)
• You need an ISO image of an OS
– Because no OSs are provided with Virtual PC
• Virtual PC creates two files for each virtual machine:
– A .vhd file, which is the actual virtual hard disk
– A .vmc file, which keeps track of configurations you
make to that disk
• See what type of physical machine your virtual
machine thinks it’s running
– Open the Virtual PC Console, and click Settings
