Document

Report
BACS 371
Computer Forensics
File Systems 2
NTFS File Systems
File Systems
(See http://www.ntfs.com)


A method for storing and organizing computer files and the
data they contain to make it easy to find and access them
File System Types

FAT (File Allocation Table)






FAT12
FAT16
FAT32
exFAT
NTFS (New Technology File System)
Functions



Manage “free space”
Allocate clusters to file
Track time (MAC – Modify, Access, Create)
NTFS Characteristics
 File
Size
16 exabytes minus 1 KB (264 minus 1KB)
 Reality 16 terabytes minus 64 KB (244 minus 64KB)
 Theoretically
 Volume
Size
 Theoretically
256 terabytes minus 64 KB (232 clusters minus 1
cluster)
 Reality 16 terabytes
 Files
per Volume
 4,294,967,295
(232 minus 1 file)
NTFS Architecture
Always at
cluster 0
MFT can be
anywhere
after boot
sector
File attributes are
stored here. No fixed
structure
MFT copy can
be anywhere
after boot
sector
Notice that the end of sector marker is 55 AA.
You can look for this to find boot sectors for NTFS and
DOS.
NTFS Boot Sector






00 10
3B
Jump Instruction
03 10
11 10
36 10
84 10
510 10
8B
25B
48B
426B
2B
OEM ID
Bios Parameter Block (BPB)
Extended BPB
Bootstrap Code.
End of Sector Marker (55AA)
Boot sector always located a cluster 0 of partition
NTFS BIOS
Parameter
Block
NTFS Boot Sector
Many fields are not important, but these are the key
ones to know about.
 11 10
 13 10
 21 10
 40 10
 48 10
 56 10
 64 10
 72 10
Bytes per sector (2 bytes)
Sectors per Cluster (1 byte)
Media descriptor. F8: HD; F0: HD Floppy (1B)
Total sectors (8 bytes)
Logical cluster number for the MFT (8 bytes)
Logical cluster number copy of the MFT (8 bytes)
Clusters per MFT Record (1 byte)
Volume serial (8 bytes)
NTFS Boot Sector

WinHex allows access to
an interpreted NTFS
Boot Sector.
 Use
the Access Tab.
NTFS Bios Parameter Block
11 10 Bytes per sector: 00 02  020016 = 51210
13 10 Sectors per cluster:
Don’t forget – Little Endian!
0816
= 810
NTFS Bios Parameter Block


21 10: Media Descriptor: F8 is hard drive, F0 is
floppy.
40 10 Total number of sectors:
F7AF4E0900000000  000000094EAFF7 
156,151,799 sectors, i.e., ~80GB
NTFS Bios Parameter Block


48 10: Logical cluster number for MFT copy 1:
cluster C7FE9 (File $MFT)
56 10: Logical cluster number for MFT copy 2:
cluster 40029D
NTFS Bios Parameter Block


64 10: Clusters per MFT record: F6
72 10: Volume Serial Number
Master File Table (MFT)




Is itself a file!
An array of records constituting a database of all
files in system (including a record of the MFT itself)
Each record is usually 1024 bytes
First 16 records contain volume-specific information
 NTFS

Metadata Files
Remaining records are related to specific files
found in the file system
NTFS Metadata Entries
System
File
File
Name
MFT
Record
Master file
table
$Mft
0
Contains one base file record for each file and folder on an NTFS volume. If
the allocation information for a file or folder is too large to fit within a
single record, other file records are allocated as well.
Master file
table 2
$MftMirr
1
A duplicate image of the first four records of the MFT. This file guarantees
access to the MFT in case of a single-sector failure.
Log file
$LogFile
2
Contains a list of transaction steps used for NTFS recoverability. Log file size
depends on the volume size and can be as large as 4 MB. It is used by
Windows NT/2000 to restore consistency to NTFS after a system failure.
Volume
$Volume
3
Contains information about the volume, such as the volume label and the
volume version.
Attribute
definitions
$AttrDef
4
A table of attribute names, numbers, and descriptions.
Root file
name index
$
5
The root folder.
Cluster
bitmap
$Bitmap
6
A representation of the volume showing which clusters are in use.
Boot sector
$Boot
7
Includes the BPB used to mount the volume and additional bootstrap loader
code used if the volume is bootable.
Bad cluster
file
$BadClus
8
Contains bad clusters for the volume.
Security file
$Secure
9
Contains unique security descriptors for all files within a volume.
Upcase
table
$Upcase
10
Converts lowercase characters to matching Unicode uppercase characters.
NTFS
extension
file
$Extend
11
Used for various optional extensions such as quotas, reparse point data, and
object identifiers.
12–15
Reserved for future use.
Purpose of the File
MFT Record






MFT Record entries are associated with each file and
directory in the system.
A single file/directory can occupy from 1 to 4 MFT
records (usually just 1)
An MFT entry is made up of a header, and a series of
attributes.
MFT entry attributes are loosely defined.
Each attribute is preceded by the attribute header.
The attribute header identifies
Type of attribute.
 Size.
 Name.

MFT Record Structure




The attribute header gives basic information about
the attribute.
A resident attribute is stored in the MFT entry.
A non-resident entry is stored in a cluster outside
the MFT.
This example shows 3 attributes.
MFT Record Structure
Some attributes are actually stored in the MFT, others
are pointed to from the MFT
 Resident attributes are stored in MFT record.
 Non-resident attributes are stored in cluster runs.
A cluster run consists of consecutive clusters and are
identified by starting cluster and run length.
 NTFS distinguishes between Virtual Cluster Numbers and
Logical Cluster Numbers.




LCN * (#sectors in cluster) = sector number
LCN 0 is first cluster in the volume (boot sector).
VCN 0 refers to the first cluster in a cluster run.
MFT Record Structure





Each attribute type within an MFT record is
identified by a code number.
A single MFT entry can have multiple attributes of
the same type.
The attribute content sizes of attributes can be of
different sizes (depending on what type they are).
Resident attributes (such as Standard Information,
File Name, and Data) are stored locally.
Non-Resident attributes are stored as a starting
cluster number and a run length.
NTFS File Attributes
Attribute Type
Description
Standard
Information
Includes information such as timestamp and link count.
Attribute List
Lists the location of all attribute records that do not fit in the MFT record.
File Name
A repeatable attribute for both long and short file names. The long name of the file
can be up to 255 Unicode characters. The short name is the 8.3, case-insensitive
name for the file. Additional names, or hard links, required by POSIX can be
included as additional file name attributes.
Security
Descriptor
Describes who owns the file and who can access it.
Data
Contains file data. NTFS allows multiple data attributes per file. Each file typically has
one unnamed data attribute. A file can also have one or more named data
attributes, each using a particular syntax.
Object ID
A volume-unique file identifier. Used by the distributed link tracking service. Not all
files have object identifiers.
Logged Tool
Stream
Similar to a data stream, but operations are logged to the NTFS log file just like NTFS
metadata changes. This is used by EFS.
Reparse Point
Used for volume mount points. They are also used by Installable File System (IFS)
filter drivers to mark certain files as special to that driver.
Index Root
Used to implement folders and other indexes.
Index Allocation
Used to implement folders and other indexes.
Bitmap
Used to implement folders and other indexes.
Volume
Information
Used only in the $Volume system file. Contains the volume version.
Volume Name
Used only in the $Volume system file. Contains the volume label.
$MFT Template
MFT Records for directories



Folders contain index data.
Small folders reside within the MFT record
Larger folders have an index structure to other data
blocks. They use a B-tree structure.
MFT Small File Entry
The master file table allocates a certain amount of space for each file record.
The attributes of a file are written to the allocated space in the MFT. Small files
and directories (typically < 800 bytes), such as the file illustrated in next figure,
can entirely be contained within the master file table record.
NTFS Multiple Data Streams

For compatibility with Mac OS







Fork
Executable
In NTFS, unlimited number of streams
A data stream is not displayed when you open a text file in a
text editor
Must examine the MFT for the file to see if there is a ‘:’
following the file name
Copy to FAT includes only 1st Stream
Example


Innocuousfile.txt
Innocuousfile.txt:hiddenporn
ADS Example
File System Comparisons
Criteria
Operating System
NTFS v.5
exFat
FAT32
FAT16
Windows 2000
Windows XP
Vista, Win 7
Windows XP
Vista, Win 7
Mac OSX
Windows 98
Windows ME
Windows 2000
Windows XP
Vista, Win 7, Mac OSX
DOS
All versions of
Microsoft Windows
Limitations
Max Volume Size
2TB
128 PetaByte
2TB
2GB
Nearly Unlimited
Nearly Unlimited
Nearly Unlimited
~65000
Limit Only by
Volume Size
16 Exabytes
4GB
2GB
Max Clusters Number
Nearly Unlimited
Nearly Unlimited
268435456
65535
Max File Name Length
Up to 255
Up to 255
Up to 255
Standard - 8.3
Extended - up to 255
Max Files on Volume
Max File Size
File System Features
Criteria
Unicode File Names
NTFS5 NTFS FAT32
FAT16
Unicode Character Set
Unicode Character Set
System Character Set
System Character Set
MFT Mirror File
MFT Mirror File
Second Copy of FAT
Second Copy of FAT
Boot Sector Location
First and Last Sectors
First and Last Sectors
First Sector
First Sector
File Attributes
Standard and Custom
Standard and Custom
Standard Set
Standard Set
Alternate Streams
Yes
Yes
No
No
Compression
Yes
Yes
No
No
Encryption
Yes
No
No
No
Object Permissions
Yes
Yes
No
No
Disk Quotas
Yes
No
No
No
Sparse Files
Yes
No
No
No
Reparse Points
Yes
No
No
No
Volume Mount Points
Yes
No
No
No
256 Char
256 Char
256 Char
8.3 Names
System Records Mirror
File Names
Overall Performance
Criteria
NTFS5
NTFS
FAT32
FAT16
Built-In Security
Yes
Yes
No
No
Recoverability
Yes
Yes
No
No
Performance
Low on small
volumes
High on Large
Low on small
volumes
High on Large
High on small
volumes
Low on large
Highest on small
volumes
Low on large
Disk Space
Economy
Max
Max
Average
Minimal on large
volumes
Fault Tolerance
Max
Max
Minimal
Average

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