91.580.203 Computer & Network Forensics Xinwen Fu Chapter 7/8 File Systems - Supplementary Materials.

91.580.203 Computer & Network

Forensics

Xinwen Fu

Chapter 7/8File Systems - Supplementary Materials

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Outline More on recovering secret data

Rename files/directories Delete files/directories Copy files/directories Print files Format a disk

FAT file system Windows registry NTFS file system

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Renaming Files Rename files and/or file extensions Example:

Rename extortion_letter.doc to fuzzy_bunny.jpg People looking for incriminating evidence

probably won’t check a picture file called fuzzy_bunny.jpg

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Rename Files (Cont.) File header implies the file type Check the real file type by hex editor

WinHex or XVI32 File type

424D - .bmp D0CF - .doc

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Copying Files Scenario #1: Copying a file to a floppy

disk or hard disk If you run out of space, the pointer to the file is

removed, but the data that was copied to the sectors is left in place

Scenario #2: Computer crashes while copying a file Again, the file contents copied to the

unallocated sectors will exist, but the pointer to the data will not have been created

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Printing a File When printing a file, it is spooled to the hard disk

before it is printed Spooling involves copying the file to a temporary

location, printing it, then deleting it After the temporary file is deleted, the data still

exists on disk

Windows XP spool folder: C:\WINNT\System32\spool\PRINTERS

1. Click Start, and then click Printers and Faxes2. On the File menu, click Server Properties3. Click the Advanced tab

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Temporary Internet Files Internet explorer stores copies of

webpages, images, and media for faster view later

Default Windows XP Temporary Internet Files folderC:\Documents and Settings\fu\Local Settings\Temporary Internet Files Tools -> General -> Browsing history ->

Settings -> View files

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Formatting a Disk When a disk is quick formatted, the file

table on the disk is cleared, but the data on the disk is left in place

Again, similar to deleting all the files on a disk

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Hiding Folders (DoS/Windows 95) Create files or directories with non-printable

characters [1][2] Example: At a DOS prompt, type the character Alt-255

using the numeric keypad. This will insert a “blank space” character, but it is not an actual space

If you show a directory listing, you can see the file/directory exists, but you might not know exactly how many “non-printing” characters exist, or their location within the file name

You can still access the directory via the Windows Explorer and similar graphical tools

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Attributes In Windows, set the “hidden” attribute on

a file or directory Can still view files if the “Show hidden

files and folders” option is checked in Windows Explorer

Other tools may or may not display hidden files

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Hiding Folders (Unix) In Unix, rename a file or directory starting with a

“.” Example: mv important.doc .important.doc Can still be viewed by listing all files “ls –a” A Linux system for you to play with

putty – mercury.cs.uml.edu user ???; passwd ???

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Swap Space Swap Space (also called a page file) is used to

increase the amount of memory available to the system

The total memory available (real RAM and the swap space) is called virtual memory

Information is constantly being written to memory, and therefore to the hard disk

Information can then be extracted from this file

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Core Dumps Core dumps are created on Unix systems

when a process or program generates a fault

The core dump will contain all the data from CPU registers and memory at the time of the fault

Information can then be extracted from core dump

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RAM Slack is the area from the end of the file to the end of that sector.

- Comes from RAM

RAM Slack

Cluster 2 Cluster 2

Cluster 2RAM Slack

File File

http://www.forensics-intl.com/def6.html

Cluster Size = 8 sectors

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Cluster 2 Cluster 2

Cluster 2 Cluster 2 Cluster 2RAM Slack

Residual Slack

Residual data slack is the area from the end of RAM slack to the end of the cluster – whatever was on the media before

File File

Residual Data Slack

Cluster Size = 8 sectors

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Slack Space A cluster is the smallest logical allocation unit A sector is the smallest physical allocation unit

When files are deleted, both the deleted data and the data in slack space still exists

When a file is wiped from the system (permanently removed), any data in the slack space still exists Wipe tool: EZ Wipe

The data in the slack space will only be removed when it is overwritten, or it is explicitly removed A list of tools: Eraser, etc.

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FTK Imager to Check Deleted Files File -> Add Evidence Item -> Physical

Drive In class exercise

Create a file Delete the file and empty recycler Use FTK imager to load the drive and check the

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Outline More on recovering secret data FAT file system

Write Delete Reformat

Windows registry NTFS file system

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What areas change when a FILE is written?

Root C

Reserved

Writing a file

VBR: Volume Boot Record

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File Allocation Table (FAT) A list of entries that map to each cluster

on the partition. Each entry records one of five things: the address of the next cluster in a chain a special end of file (EOF) character that

indicates the end of a chain a special character to mark a bad cluster a special character to mark a reserved cluster a zero to note that that cluster is unused

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Directory Table A special type of file that represents a directory

(nowadays commonly known as a folder) Each file or directory stored within it is

represented by a 32 byte entry in the table. Each entry records name, extension, attributes (archive, directory, hidden,

read-only, system and volume), the date and time of creation, the address of the first cluster of the the address of the first cluster of the file/directory's data and finally the size of the file/directory's data and finally the size of the file/directory.file/directory.

Aside from the Root Directory Table in FAT12 and FAT16 file systems which occupies the special Root Directory Region location, all Directory Tables are stored in the Data Region

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Root C

Reserved

Filename Start Cluster SizeFILE 2 1024 Unused Directory Entry Unused Directory Entry

Directory entry is created

Writing a file

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Root C

Reserved

FATs are updated

Writing a file

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Root C

Reserved

FATs are updated

FILE contents written to data area

Writing a file

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Root C

Reserved

What areas change when a FILE is deleted?

Deleting a file

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Root C

Reserved

Filename Start Cluster Size ILE 2 1024 Unused Directory Entry Unused Directory Entry

First character of the Directory

entry is changed to (0xe5)

Deleting a file

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Root C

Reserved

FAT entries are ed

entry is changed to

Deleting a file

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Root D

Reserved

FAT entries are ed

entry is changed to

Data area is not changed !

Deleting a file

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Root C

Reserved

What areas change when a partition is reformatted?

Reformatting (DOS 6.22)

http://www.increa.com/articles/DestroyMagneticData/index.htm

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Root C

Reserved

Three areas change when a partition is reformatted

Filename Start Cluster SizeUnused Directory Entry Unused Directory Entry Unused Directory Entry

Root Directory entries are ed

Reformatting

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Root C

Reserved

FAT entries are ed

Reformatting

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Root C

Reserved

Boot Record is written

FAT entries are ed

Reformatting

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Root C

Reserved

Boot Record is written

FAT entries are ed

Data area is not changed

Reformatting

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Outline More on recovering secret data FAT file system Windows registry NTFS file system

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Windows Registry What is it:

A central hierarchical database to store information necessary to configure the system for one or more users, applications and hardware devices

Replaces AUTOEXEC.BAT, CONFIG.SYS and INI files

First introduced in Windows 3.1 for storing OLE Settings (pre 1995)

View Windows Registry: regedit or Ice Sword

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Windows Registry There are five root keys

HKEY_CLASSES_ROOT (HKCR) HKEY_CURRENT_USER (HKCU) HKEY_LOCAL_MACHINE (HKLM) HKEY_USERS (HKU) HKEY_CURRENT_CONFIG (HKCC)

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Two are “Master” keys HKEY_LOCAL_MACHINE

(HKLM) Configuration data

describing hardware and software installed on the computer

HKEY_USERS (HKU) Configuration data for

each user that logs into the computer

http://www.antirootkit.com/software/IceSword.htm

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Three are derived from “Master” keys Architecture HKEY_CLASSES_ROOT

File Associations and OLE HKEY_CURRENT_USER

Currently logged on user HKEY_CURRENT_CONFIG

Current hardware profile

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HKEY_CLASSES_ROOT File Associations and OLE From HKLM\Software\Classes

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HKEY_CURRENT_USER Currently logged on user From HKU\SID (security identifier) of current user User vs SID: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\

CurrentVersion\ProfileList

http://support.microsoft.com/kb/243330http://en.wikipedia.org/wiki/Security_Identifier

http://support.microsoft.com/kb/154599

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HKEY_CURRENT_CONFIG Current hardware profile From HKLM\System\CurrentControlSet\Hardware Profiles\

Current

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Windows Registry Wealth of investigative information

Registered Owner Registered Organization Shutdown Time Recent DOCs Most Recent Used (MRU) List Typed URLs Previous Devices Mounted Software Installed

http://support.microsoft.com/kb/256986/EN-US/

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Registry Tools Registry Reader: Access Data Encase Windows

Regedit Regedt32

Freeware tools Never work on the original Make a copy

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Registry Locations See system files: file explorer -> tools -> folder options -> view Windows NT, 2000, XP, and Server 2003 The following Registry files are stored in %SystemRoot%\System32\Config\:

Sam – HKEY_LOCAL_MACHINE\SAM Security – HKEY_LOCAL_MACHINE\SECURITY Software – HKEY_LOCAL_MACHINE\SOFTWARE System – HKEY_LOCAL_MACHINE\SYSTEM Default – HKEY_USERS\.DEFAULT

The following files are stored in each user's profile folder: %UserProfile%\Ntuser.dat – HKEY_USERS\<User SID> %UserProfile%\Local Settings\Application Data\Microsoft\Windows\Usrclass.dat (path

is localized) – HKEY_USERS\<User SID>_Classes Windows 95, 98, and Me The registry files are named User.dat and System.dat and are stored in the C:\

WINDOWS\ directory. In Windows ME Classes.dat was added. Windows 3.11 The registry file is called Reg.dat and is stored in the C:\WINDOWS\ directory.

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Outline More on recovering secret data FAT file system Windows registry NTFS file system

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NTFS Each system component is a file - even system

information The most important file on NTFS is named MFT

( Master File Table) - the common table of files Centralized directory of all remaining disk files and itself Divided into records of the fixed size (usually 1 KBytes) Each record corresponds to some file The first 16 files are housekeeping with a fixed position;

and they are inaccessible to the operating system; They are named metafiles and the very first metafile is

MFT itself The second copy of the first 3 records, for reliability is

stored exactly in the middle of the disk The remaining MFT-file can be stored as well as any other

file at any places of the disk

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NTFSMaster Boot Record

Volume Boot record

MFT is divided into records of the fixed size (usually 1 Kbytes)

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System FileFile Name

MFT Record

Purpose of the File

Master file table $Mft 0 Contains one base file record

Master file table 2 $MftMirr 1 A duplicate image of the first three records of the MFT

Log file $LogFile 2 Contains a list of transaction steps used for NTFS recoverability.

Volume $Volume 3 Contains information about the volume

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 (one bit refers to one cluster)

Boot sector $Boot 7 Includes the BIOS Parameter Block (BPB)

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

12–15 Reserved for future use

NTFS System Files (Metadata Files)

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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. _DATA_ attribute that describes "data runs“, clusters used by the file

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.

NTFS File Attributes

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Storing Files in NTFS $LogFile metadata file is updated

–Transaction steps are logged

–Used to “roll back” if necessary

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Deleted File Parent directory

Index entry removed $BITMAP attribute updated*

MFT file record marked available MFT $BITMAP attribute Updated $Bitmap Metadata file updated if non-resident

clusters Resident clusters: files can be stored within a MFT

record No-resident clusters: files cannot be stored within a

MFT record

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Deleted File (Cont.)

Index entry removed

File Record (MYFILE.HLP)

File Record (SYSTEM.DLL)

File Record (README.TXT)

Directory Record (Recycler)

Index Entry (S-1-5-21-3xxxxxx)

Directory Record (S-1-5-21-3xxxxxx)

File Record

Directory Record (MYFILES)

Index Entry (README.TXT)

Index Entry (SYSTEM.DLL)

File Record Entry

6 File Record($BITMAP)

[Parent]

Index Entry (MYFILE.HLP)

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Deleted File (Cont.)

MFT record marked available 215

File Record Entry

File Record

[Parent]File Record Entry

6 File Record($BITMAP)

[Parent]

File Record (MYFILE.HLP) [214]216

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$MFT Attribute Updated

File RecordHeader

$MFT$STANDARD_INFORMATION

$DATA $BITMAP

11111111 11111111 0000000011100111 00000001 0000000000000000 00000000 0000000000000000 00000000 00000000The bytes are read from right to left

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File Deleted

$Bitmap updated215

File Record (MYFILE.HLP)

File Record Entry

File Record

[Parent]

File Record Entry

6 File Record ($Bitmap)

[Parent]

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Recovering Deleted Files Software Tools

FTK Toolkits GetDataback (Runtime) R-studio CIA Unerase Etc

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Deleted vs “Recycled” Deleted or “Recycled”

Sent to Recycle Bin Deleted from the Recycle Bin Deleted bypassing the Recycle Bin – shift+del

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Win2K/XP Recycle Bin “Recycler” Folder for NTFS

Configure to see hidden and system files from explorer

SID named subdirectory contains: INFO2 Desktop.ini Place holder(s)

Use FTK Imager to load the Recycler folder for view

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NTFS Recycle Bin

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Placeholder(s)

Entry for each deleted item: Hidden from view in GUI environment Date & time unchanged from original file

If a subdirectory is deleted only one placeholder is made

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Placeholder(s)

D<original drive letter><#>.<original extension>

DC1.TXTDC2.JPGDC3.BMP

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INFO2 File 800 Byte Entry is made for each

Recycled object Recycled date Original path and filename Place holder drive letter and #

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INFO2 File (Cont.)

ASCII File

Drive Letter

Deletion Time

File SizeUnicode

File Name

Record Size

Record ID

Start of the Record

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Recycled date and time issue Windows saves time stamps in “FILETIME”

format. FILETIME format is the number of ticks, in 100ns increments, since 00:00 1 Jan, 1601 (UTC).

Recycle Bin tools (X-Ways Trace, IEHistory, Datalifter) will convert the time for you

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Desktop.ini A folder configuration file

Created when Recycle Bin is created

Only modified if recycle bin is EMPTIED All Date / Time information updated when bin

is emptied

http://www.xs4all.nl/~hwiegman/desktopini.html

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Recovering From Recycle Bin When an object is sent to the recycle bin, the MFT record

for the deleted object is simply changed. The $Filename attribute is changed to: Change the filename to the placeholder name that appears in

the recycle bin (placeholder format: D + drive letter + #) Change the record number of the parent directory from the old

parent directory, to the sid-named directory in the recycler directory.

Copy placeholders to separate drive Copy INFO2 file; use utility to parse out date /

time data X-Ways Trace - http://www.x-ways.net/trace/index-m.html Datalifter IE History

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Summary Deleting and formatting on a Hard Drive

does not touch the data area Often evidence can be found in deleted

files, and the recycle bin System clocks and default timezone

settings are very important

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Review What happens to deleted FAT files What about formatting? What happens to deleted NTFS files? Recovering deleted files

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References1. Nathan Heald, http://dos.rsvs.net/DOSPAGE/DEBUG.HTM, 20082. IronGeek, ALT+NUMPAD ASCII Key Combos: The α and Ω of Creating

Obscure Passwords, 20073. Description of the Microsoft Windows registry,

http://support.microsoft.com/kb/256986/EN-US/, August 12, 2005 4. Dmitrey Mikhailov, NTFS file system, http://www.digit-life.com/articles/ntfs/,

2004 5. NTFS - New Technology File System designed for Windows NT, 2000, XP,

http://www.ntfs.com/, 20056. Brian Mork, Destroying Data on Magnetic Disks - Linux or Windows, 20057. How the Recycle Bin Stores Files,

http://support.microsoft.com/kb/136517/en-us, December 16, 2004 8. The Mysterious Recycle Bin,

http://www.infocellar.com/winxp/Recycle-Bin.htm, 20069. Anders Svensson, Computer Forensics Applied to Windows NTFS Systems,

http://www.dsv.su.se/research/seclab/pages/pdf-files/2005-x-268.pdf, April 2005

10. Keith J. Jones, Forensic Analysis of Microsoft Windows Recycle Bin Records, http://www.e-fense.com/helix/Docs/Recycler_Bin_Record_Reconstruction.pdf, 5/6/03

91.580.203 Computer & Network Forensics Xinwen Fu Chapter 7/8 File Systems - Supplementary Materials.

temporary file

picture file

file header

file menu

file table

file contents

page file

disk slide

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