skins_ntfs.txt

linux下开发的针对所有磁盘的数据恢复的源码

                       The NTFS File System

             Sleuth Kit Implementation Notes (SKINs)
                     http://www.sleuthkit.org

                          Brian Carrier
                     Last Updated: Sept 2008



INTRODUCTION
=======================================================================
The NTFS file system is used in all critical Microsoft Windows
systems.  It is an advanced file system that makes it different
from the UNIX file systems that the original TCT was designed for.
This document gives a quick overview of NTFS and how it was
implemented.  The biggest difference is the use of Alternate Data
Streams (ADS) when specifying a meta data structure.

The Sleuth Kit allows one to investigate an NTFS image in the same
ways as any UNIX image, including:

  - Creation of ASCII timeline of file activity
  - Cluster analysis and mapping between clusters and MFT entries
  - MFT analysis and mapping between MFT entries and file names
  - File and directory level analysis including deleted files


NTFS OVERVIEW
=======================================================================
This provides a quick introduction to the NTFS file system.  The
terms used are different then with other file systems.  For a full
overview of the file system, refer to the "Inside Windows 2000"
book by Solomon and Russinovich and for details of the file system
structures, refer to the NTFS Source Forge project at:

	http://linux-ntfs.sourceforge.net/ntfs/index.html


MFT
-----------------------------------------------------------------------
The Master File Table (MFT) contains entries that describe all
system files, user files, and directories.   The MFT even contains
an entry (#0) that describes the MFT itself, which is how we
determine its current size.  Other system files in the MFT include
the Root Directory (#5), the cluster allocation map, Security
Descriptors, and the journal.


MFT ENTRIES
-----------------------------------------------------------------------
Each MFT entry is given a number (similar to inode numbers in UNIX).
The user files and directories start at MFT #25.  The MFT entry
contains a list of attributes.  Example attributes include "Standard
Information" which stores data such as MAC times, "File Name" which
stores the file or directories name(s), $DATA which stores the
actual file content, or "Index Alloc" and "Index Root" which contain
directory contents stored in a B-Tree.

Each type of attribute is given a numerical value and more than
one instance of a type can exist for a file.  The "id" value for
each attribute allows one to specify an instance.  A given file
can have more than one "$Data" attribute, which is a method that
can be used to hide data from an investigator.  To get a mapping
of attribute type values to name, use the 'fsstat' command.  It
displays the contents of the $AttrDef system file.

Each attribute has a header and a value and an attribute is either
resident or non-resident.  A resident attribute has both the header
and the content value stored in the MFT entry.  This only works
for attributes with a small value (the file name for example).
For larger attributes, the header is stored in the MFT entry and
the content value is stored in Clusters in the data area.  A Cluster
in NTFS is the same as FAT, it is a consecutive group of sectors.
If a file has too many different attributes, an "Attribute List"
is used that stores the other attribute headers in additional MFT
entries.


FILES
-----------------------------------------------------------------------
Files in NTFS typically have the following attributes:

  - $STANDARD_INFORMATION (#16): Contains MAC times, security ID,
    Owners ID, permissions in DOS format, and quota data.
  - $FILE_NAME (#48): Contains the file name in UNICODE, as well
    as additional MAC times, and the MFT entry of the parent
    directory.
  - $OBJECT_ID (#64): Identifiers regarding the files original
    Object ID, its birth Volume ID, and Domain ID.
  - $DATA (#128): The raw content data of the file.

When a file is deleted, the IN_USE flag is cleared from the MFT entry,
but the attribute contents still exist. 


DIRECTORIES
-----------------------------------------------------------------
Directories in NTFS are indexed to make finding a specific entry
in them faster.  By default, they are stored in a B-Tree sorted in
alphabetical order.  There are two attributes that describe the
B-Tree contents.  Directories in NTFS typically have the following
attributes:

  - $STANDARD_INFORMATION (#16): See above
  - $FILE_NAME (#48): See above
  - $OBJECT_ID (#64): See above
  - $INDEX_ROOT (#144): The root of the B-Tree.  The $INDEX_ROOT
    value is one more more "Index Entry" structures that each
    describe a file or directory.  The "Index Entry" structure
    contains a copy of the "$FILE_NAME" attribute for the file or
    sub-directory.
  - $INDEX_ALLOCATION (#160): The sub-nodes of the B-Tree.  For
    small directories, this attribute will not exist and all
    information will be saved in the $INDEX_ROOT structure.  The
    content of this attribute is one or more "Index Buffers".  Each
    "Index Buffer" contains one or more "Index Entry" structures,
    which are the same ones found in the $INDEX_ROOT.
  - $BITMAP (#176): This describes which structures in the B-Tree
    are being used.

When files are deleted from a directory, the tree node is removed
and the tree is resorted.  Therefore, the "Index Entry" for the
deleted file maybe written over when the tree is resorted.  This
is different than what is usually seen with UNIX and FAT file
systems, which always have the original name and structure until
a new file is created.  Also, when the tree is resorted, a file
that is on the bottom of the tree can be moved up and a deleted
file name will exist for the original location (even though it was
never deleted by a user).



USING THE SLEUTH KIT WITH NTFS
=======================================================================
The Sleuth Kit allows one to view all aspects of the NTFS structure.
The biggest difference with using The Sleuth Kit with NTFS instead
of UNIX file systems is the attributes.  With UNIX you only need
to reference the inode number because there is only one piece of
content for the file.  With NTFS, one can either specify just the
MFT number and the default data attribute is used or the type can
be specified by adding it to the end of the MFT entry, 36-128 for
example.  If more than one attribute of the same type exists, then
the id can be used after the type, 36-128-5 for example.


All Sleuth Kit tools can take MFT values in any of the above formats
and output from the tools will also be in one of the above formats.
For example, the 'istat' tool will list all attributes a file has.
To get the details of MFT entry 49, use:

    # istat -f ntfs ntfs.dd 49
    MFT Entry: 49
    Sequence: 2
    Allocated
    UID: 0
    DOS Mode: File
    Size: 15
    Links: 1
    Name: multiple.txt

    $STANDARD_INFORMATION Times:
    File Modified:  Mon Nov  5 19:58:27 2001
    MFT Modified:   Mon Nov  5 19:58:27 2001
    Accessed:       Mon Nov  5 19:58:27 2001

    $FILE_NAME Times:
    Created:        Mon Nov  5 19:57:29 2001
    File Modified:  Mon Nov  5 19:57:29 2001
    MFT Modified:   Mon Nov  5 19:57:29 2001
    Accessed:       Mon Nov  5 19:57:29 2001

    Attributes: 
    Type: $STANDARD_INFORMATION (16-0)   Name: N/A   Resident   size: 72
    Type: $FILE_NAME (48-2)   Name: N/A   Resident   size: 90
    Type: $OBJECT_ID (64-3)   Name: N/A   Resident   size: 16
    Type: $DATA (128-1)   Name: $Data   Resident   size: 15
    Type: $DATA (128-5)   Name: overhere   Resident   size: 26


We see that it has 5 attributes, all of them are resident (notice
the small sizes).  Two of the attributes are $DATA attributes (128-1
and 128-5).  The full name of 128-1 is 'multiple.txt' and the full
name of 128-5 is 'multiple.txt:overhere'.

The following command would display the default data attribute
(128-1):
	# icat -f ntfs ntfs.dd 49

The following is the same:
	# icat -f ntfs ntfs.dd 49-128-1

The following displays the other data stream: 
    # icat -f ntfs ntfs.dd 49-128-5

As an additional example, the raw format of the $FILE_NAME attribute
can be viewed using:
    # icat -f ntfs ntfs.dd 49-48-2

The output of the above command would be a combination of UNICODE
characters and other binary data (I would recommend just using the
output of the istat command for this type of data).
    

The output of the 'fls' command is similar:
    # fls -f ntfs ntfs.dd
    <...>
    r/r 48-128-1:   test-1.txt
    r/r 49-128-1:   multiple.txt
    r/r 49-128-5:   multiple.txt:NEW
    r/r 50-128-1:   test-2.txt
    <...>
This allows you to easily identify all data streams.  

Note that Autopsy can automate this process for you and allows you
to view all attributes.

   http://www.sleuthkit.org/autopsy



WHAT THE SLEUTH KIT CANNOT CURRENTLY DO
=======================================================================
There are a few things that The Sleuth Kit is not yet able to do
with NTFS:

- The Security Descriptors are not yet analyzed.  Therefore, the
  exact ACLs of the object can not be displayed.
- Directories that are indexed by a descriptor other than the file
  name, are not supported.
- Encrypted files are not supported

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Copyright (c) 2002-2008 by Brian Carrier.  All Rights Reserved