Difference between pages "Hashing" and "Windows Prefetch File Format"

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'''Hashing''' is a method for reducing large inputs to a smaller fixed size output. When doing forensics, typically cryptographic hashing algorithms like [[MD5]] and [[SHA-1]] are used. These functions have a few properties useful to forensics.
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A Windows Prefetch file consists of one file header and multiple file sections with different content. Not all content has an obvious forensic value.
  
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== Tools ==
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As far as have been possible to ascertain, there is no public description of the format. The description below has been synthesised from examination
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of multiple prefetch files.
  
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There are literally hundreds of hashing programs out there, but a few related to forensics are:
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== Header ==
  
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* [[md5sum]] - Part of the [[GNU]] coreutils suite, this program is standard on many computers.
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This format has been observed on Windows XP, ...  will need to be modified for Vista/Win7 format
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* [[md5deep]] - Computes hashes, recursively if desired, and can compare the results to known values.
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{| class="wikitable"
 +
|-
 +
! Field
 +
! Offset
 +
! Length
 +
! Type
 +
! Notes
 +
|-
 +
| H1
 +
| 0x0000
 +
| 4
 +
| DWORD
 +
| ? Probably a version number, identifying the file structure. Observed values: 0x11 - Windows XP; 0x17 - Vista, Windows 7
 +
|-
 +
| H2
 +
| 0x0004
 +
| 4
 +
| DWORD
 +
| ? Probably a file magic number. Only observed value: 0x41434353
 +
|-
 +
| H3
 +
| 0x0008
 +
| 4
 +
| DWORD?
 +
| ? Observed values: 0x0F - Windows XP, 0x11 - Windows 7
 +
|-
 +
| H4
 +
| 0x000C
 +
| 4
 +
| DWORD
 +
| Prefetch file length.
 +
|-
 +
| H5
 +
|0x0010
 +
| 60
 +
| USTR
 +
| Name of executable as Unicode string, truncated after character 29 if necessary, and terminated by U+0000. As it appears in the prefetch file file name.
 +
|-
 +
| H6
 +
|0x004C
 +
|4
 +
|DWORD
 +
|The prefetch hash, as it appears in the pf file name.
 +
|-
 +
| H7
 +
|0x0050
 +
|4
 +
|?
 +
|? Observed values: 0 for almost all prefetch files (XP); 1 for NTOSBOOT-B00DFAAD.pf (XP)
 +
|-
 +
| H8
 +
| 0x0054
 +
| 4
 +
| DWORD
 +
| Offset to section A
 +
|-
 +
| H9
 +
| 0x0058
 +
| 4
 +
| DWORD
 +
| ? Nr of entries in section A
 +
|-
 +
| H10
 +
| 0x005C
 +
| 4
 +
| DWORD
 +
| Offset to section B
 +
|-
 +
| H11
 +
| 0x0060
 +
| 4
 +
| DWORD
 +
| Nr of entries in section B
 +
|-
 +
| H12
 +
| 0x0064
 +
| 4
 +
| DWORD
 +
| Offset to section C
 +
|-
 +
| H13
 +
| 0x0068
 +
| 4
 +
| DWORD
 +
| Length of section C
 +
|-
 +
| H14
 +
| 0x006C
 +
| 4
 +
| DWORD
 +
| Offset to section D
 +
|-
 +
| H15
 +
| 0x0070
 +
| 4
 +
| DWORD
 +
| ? Probably the number of entries in the D section header
 +
|-
 +
| H16
 +
| 0x0074
 +
| 4
 +
| DWORD
 +
| Length of section D
 +
|-
 +
| H17
 +
| 0x0078
 +
| 8
 +
| FTIME
 +
| Latest execution time of executable (FILETIME)
 +
|-
 +
| H18
 +
| 0x0080
 +
| 16
 +
| ?
 +
| ? Possibly structured as 4 DWORD. Observed values: /0x00000000 0x00000000 0x00000000 0x00000000/, /0x47868c00 0x00000000 0x47860c00 0x00000000/
 +
|-
 +
| H19
 +
| 0x0090
 +
| 4
 +
| DWORD
 +
| Execution counter
 +
|-
 +
| H20
 +
| 0x0094
 +
| 4
 +
| DWORD?
 +
| ? Observed values: 1, 2, 3, 4, 5, 6 (XP)
 +
|-
 +
|}
 +
 
 +
It's worth noting that the name of a carved prefetch file can be restored using the information in field H5 and H6, and its size can be determined by field H4.
 +
 
 +
== Section A and B ==
 +
 
 +
The content of these two sections is unknown.
 +
 
 +
== Section C ==
 +
 
 +
== Section D ==

Revision as of 10:29, 14 September 2011

A Windows Prefetch file consists of one file header and multiple file sections with different content. Not all content has an obvious forensic value.

As far as have been possible to ascertain, there is no public description of the format. The description below has been synthesised from examination of multiple prefetch files.

Contents

Header

This format has been observed on Windows XP, ... will need to be modified for Vista/Win7 format

Field Offset Length Type Notes
H1 0x0000 4 DWORD  ? Probably a version number, identifying the file structure. Observed values: 0x11 - Windows XP; 0x17 - Vista, Windows 7
H2 0x0004 4 DWORD  ? Probably a file magic number. Only observed value: 0x41434353
H3 0x0008 4 DWORD?  ? Observed values: 0x0F - Windows XP, 0x11 - Windows 7
H4 0x000C 4 DWORD Prefetch file length.
H5 0x0010 60 USTR Name of executable as Unicode string, truncated after character 29 if necessary, and terminated by U+0000. As it appears in the prefetch file file name.
H6 0x004C 4 DWORD The prefetch hash, as it appears in the pf file name.
H7 0x0050 4 ? ? Observed values: 0 for almost all prefetch files (XP); 1 for NTOSBOOT-B00DFAAD.pf (XP)
H8 0x0054 4 DWORD Offset to section A
H9 0x0058 4 DWORD  ? Nr of entries in section A
H10 0x005C 4 DWORD Offset to section B
H11 0x0060 4 DWORD Nr of entries in section B
H12 0x0064 4 DWORD Offset to section C
H13 0x0068 4 DWORD Length of section C
H14 0x006C 4 DWORD Offset to section D
H15 0x0070 4 DWORD  ? Probably the number of entries in the D section header
H16 0x0074 4 DWORD Length of section D
H17 0x0078 8 FTIME Latest execution time of executable (FILETIME)
H18 0x0080 16  ?  ? Possibly structured as 4 DWORD. Observed values: /0x00000000 0x00000000 0x00000000 0x00000000/, /0x47868c00 0x00000000 0x47860c00 0x00000000/
H19 0x0090 4 DWORD Execution counter
H20 0x0094 4 DWORD?  ? Observed values: 1, 2, 3, 4, 5, 6 (XP)

It's worth noting that the name of a carved prefetch file can be restored using the information in field H5 and H6, and its size can be determined by field H4.

Section A and B

The content of these two sections is unknown.

Section C

Section D

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