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

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Windows Prefetch files, introduced in [[Windows|Windows XP]], are designed to speed up the application startup process. Prefetch files contain the name of the executable, a Unicode list of DLLs used by that executable, a count of how many times the executable has been run, and a timestamp indicating the last time the program was run. Although Prefetch is present in Windows 2003, by default it is only enabled for boot prefetching. The feature is also found in [[Windows|Windows Vista]], where it has been augmented with [[SuperFetch]], [[ReadyBoot]], and [[ReadyBoost]].
  
A Windows Prefetch file consists of one file header and multiple file sections with different content. Not all content has an obvious forensic value.
+
From [http://msdn.microsoft.com/en-us/library/windows/hardware/dn653317(v=vs.85).aspx]:
 +
* [[SuperFetch]]; analyzes per-machine usage patterns over time and optimizes the data that is kept in memory.
 +
* [[ReadyBoot]]; decreases boot time (the time from turning power on to reaching the log-on screen) by preloading the files and startup programs needed per-machine into a cache.
 +
* [[ReadyBoost]]; supports the use of flash storage devices like Universal Serial Bus (USB) flash drives and Secure Digital (SD) flash cards to boost PC performance.
 +
* [[ReadyDrive]]; supports hybrid hard disk drives.
  
As far as have been possible to ascertain, there is no public description of the format. The description below has been synthesised from examination
+
For SSD drives Prefetch is disabled by default [http://blogs.msdn.com/b/e7/archive/2009/05/05/support-and-q-a-for-solid-state-drives-and.aspx].
of multiple prefetch files.
+
  
== Characteristics ==
+
== Prefetch files ==
{| class="wikitable"
+
The Prefetch files are stored in the directory:
|-
+
<pre>
| <b>Integers</b>
+
%SystemRoot%\Prefetch
| stored in little-endian
+
</pre>
|-
+
| <b>Strings</b>
+
| Stored as [http://en.wikipedia.org/wiki/UTF-16/UCS-2 UTF-16 little-endian] without a byte-order-mark (BOM).
+
|-
+
| <b>Timestamps</b>
+
| Stored as [http://msdn2.microsoft.com/en-us/library/ms724284.aspx Windows FILETIME] in UTC.
+
|-
+
|}
+
  
== File header ==
+
The following files can be found in the Prefetch directory:
The file header is 84 bytes of size and consists of:
+
* <tt>*.pf</tt>, which are Prefetch files;
{| class="wikitable"
+
* <tt>Ag*.db</tt> and <tt>Ag*.db.trx</tt>, which are [[SuperFetch]] files;
|-
+
* <tt>Layout.ini</tt>;
! Field
+
* <tt>PfPre_*.db</tt>;
! Offset
+
* <tt>PfSvPerfStats.bin</tt>
! Length
+
! Type
+
! Notes
+
|-
+
| H1
+
| 0x0000
+
| 4
+
| DWORD
+
| Format version (see format version section below)
+
|-
+
| H2
+
| 0x0004
+
| 4
+
| DWORD
+
| Signature 'SCCA' (or in hexadecimal representation 0x53 0x43 0x43 0x4)
+
|-
+
| H3
+
| 0x0008
+
| 4
+
| DWORD?
+
| Unknown - Values observed: 0x0F - Windows XP, 0x11 - Windows 7, Windows 8.1
+
|-
+
| H4
+
| 0x000C
+
| 4
+
| DWORD
+
| Prefetch file size (or length) (sometimes referred to as End of File (EOF)).
+
|-
+
| H5
+
|0x0010
+
| 60
+
| USTR
+
| The name of the (original) executable as a Unicode (UTF-16 litte-endian string), up to 29 characters and terminated by an end-of-string character (U+0000). This name should correspond with the one in the prefetch file filename.
+
|-
+
| H6
+
|0x004C
+
|4
+
|DWORD
+
|The prefetch hash. This hash value should correspond with the one in the prefetch file filename.
+
|-
+
| H7
+
|0x0050
+
|4
+
|?
+
| Unknown (flags)? Values observed: 0 for almost all prefetch files (XP); 1 for NTOSBOOT-B00DFAAD.pf (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.
+
A Prefetch file contains the name of the application, a dash, and then an eight character hash of the location from which that application was run, and a <tt>.pf</tt> extension. The filenames should be all uppercase except for the extension. E.g. a filename for [[md5deep]] would look like: <tt>MD5DEEP.EXE-4F89AB0C.pf</tt>. If an application is run from two different locations on the drive (i.e. the user runs <tt>C:\md5deep.exe</tt> and then <tt>C:\Apps\Hashing\md5deep.exe</tt>), there will be two different prefetch files in the Prefetch folder. According to MSDN up to 128 Prefetch files can be stored in the Prefetch directory [http://blogs.msdn.com/ryanmy/archive/2005/05/25/421882.aspx].
  
=== Format version ===
+
=== File format ===
 +
Each Prefetch file has a 4-byte signature (at offset 4) "SCCA" (or in hexadecimal notation 0x53 0x43 0x43 0x41). The signature is assumed to be preceded by a 4-byte format version indicator:
 +
* 17 (0x00000011) for [[Windows XP]] and [[Windows 2003]]
 +
* 23 (0x00000017) for [[Windows Vista]], [[Windows 2008]], [[Windows 7]] and [[Windows 2012]] (note Windows 2012 has not been confirmed)
 +
* 26 (0x0000001a) for [[Windows 8|Windows 8.1]] (note this could be Windows 8 as well but has not been confirmed)
  
{| class="wikitable"
+
For more information about the file format see: [[Windows Prefetch File Format]]
|-
+
! Value
+
! Windows version
+
|-
+
| 17 (0x11)
+
| Windows XP, Windows 2003
+
|-
+
| 23 (0x17)
+
| Windows Vista, Windows 7
+
|-
+
| 26 (0x1a)
+
| Windows 8.1 (note this could be Windows 8 as well but has not been confirmed)
+
|-
+
|}
+
  
=== File information ===
+
== Metadata ==
The format of the file information is version dependent.
+
The Prefetch file contains various metadata.
 +
* The executable's name, up to 29 characters.
 +
* The run count, or number of times the application has been run.
 +
* Volume related information, like volume path and volume serial number.
 +
* The size of the Prefetch file (sometimes referred to as end of file (EOF)).
 +
* The files and directories that were used doing the application's start-up.
  
Note that some other format specifications consider the file information part of the file header.  
+
=== Timestamps ===
 +
The Prefetch file contains 2 types of timestamps
 +
* The time when the application was last ran (executed). Version 26 of the Prefetch format maintains 7 previous last run times.
 +
* The volume creation time (part of the volume information) of the volume the Prefetch file was created on.
  
==== File information - version 17 ====
+
The file system creation time of the Prefetch file indicates the first time the application was executed. Both the file system modification time of the Prefetch file and the embedded last run time indicate the last time the application was executed.
The file information – version 17 is 68 bytes of size and consists of:
+
{| class="wikitable"
+
|-
+
! Field
+
! Offset
+
! Length
+
! Type
+
! Notes
+
|-
+
|
+
| 0x0054
+
| 4
+
| DWORD
+
| The offset to section A. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0058
+
| 4
+
| DWORD
+
| The number of entries in section A.
+
|-
+
|
+
| 0x005C
+
| 4
+
| DWORD
+
| The offset to section B. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0060
+
| 4
+
| DWORD
+
| The number of entries in section B.
+
|-
+
|
+
| 0x0064
+
| 4
+
| DWORD
+
| The offset to section C. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0068
+
| 4
+
| DWORD
+
| Length of section C.
+
|-
+
|
+
| 0x006C
+
| 4
+
| DWORD
+
| Offset to section D. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0070
+
| 4
+
| DWORD
+
| The number of entries in section D.
+
|-
+
|
+
| 0x0074
+
| 4
+
| DWORD
+
| Length of section D.
+
|-
+
|
+
| 0x0078
+
| 8
+
| FILETIME
+
| Latest execution time (or run time) of executable (FILETIME)
+
|-
+
|
+
| 0x0080
+
| 16
+
| ?
+
| Unknown ? Possibly structured as 4 DWORD. Observed values: /0x00000000 0x00000000 0x00000000 0x00000000/, /0x47868c00 0x00000000 0x47860c00 0x00000000/ (don't exclude the possibility here that this is remnant data)
+
|-
+
|
+
| 0x0090
+
| 4
+
| DWORD
+
| Execution counter (or run count)
+
|-
+
|
+
| 0x0094
+
| 4
+
| DWORD?
+
| Unknown ? Observed values: 1, 2, 3, 4, 5, 6 (XP)
+
|-
+
|}
+
  
==== File information - version 23 ====
+
== Prefetch hash ==
The file information – version 23 is 156 bytes of size and consists of:
+
There are multiple known hashing functions to be used for prefetch file filename hashing, namely:
{| class="wikitable"
+
* SCCA XP hash function; used on Windows XP and Windows 2003
|-
+
* SCCA Vista hash function; used on Windows Vista
! Field
+
* SCCA 2008 hash function; used on Windows 2008, Windows 7, (possibly: Windows 2012) and Windows 8 (including 8.1)
! Offset
+
! Length
+
! Type
+
! Notes
+
|-
+
|
+
| 0x0054
+
| 4
+
| DWORD
+
| The offset to section A. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0058
+
| 4
+
| DWORD
+
| The number of entries in section A.
+
|-
+
|
+
| 0x005C
+
| 4
+
| DWORD
+
| The offset to section B. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0060
+
| 4
+
| DWORD
+
| The number of entries in section B.
+
|-
+
|
+
| 0x0064
+
| 4
+
| DWORD
+
| The offset to section C. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0068
+
| 4
+
| DWORD
+
| Length of section C.
+
|-
+
|
+
| 0x006C
+
| 4
+
| DWORD
+
| Offset to section D. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0070
+
| 4
+
| DWORD
+
| The number of entries in section D.
+
|-
+
|
+
| 0x0074
+
| 4
+
| DWORD
+
| Length of section D.
+
|-
+
|
+
| <b>0x0078</b>
+
| <b>8</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
|
+
| 0x0080
+
| 8
+
| FILETIME
+
| Latest execution time (or run time) of executable (FILETIME)
+
|-
+
|
+
| 0x0088
+
| 16
+
| ?
+
| Unknown
+
|-
+
|
+
| 0x0098
+
| 4
+
| DWORD
+
| Execution counter (or run count)
+
|-
+
|
+
| 0x009C
+
| 4
+
| DWORD?
+
| Unknown
+
|-
+
|
+
| <b>0x00A0</b>
+
| <b>80</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
|}
+
  
==== File information - version 26 ====
+
=== SCCA XP hash function ===
The file information – version 26 is 224 bytes of size and consists of:
+
A Python implementation of the SCCA XP hash function:
{| class="wikitable"
+
|-
+
! Field
+
! Offset
+
! Length
+
! Type
+
! Notes
+
|-
+
|
+
| 0x0054
+
| 4
+
| DWORD
+
| The offset to section A. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0058
+
| 4
+
| DWORD
+
| The number of entries in section A.
+
|-
+
|
+
| 0x005C
+
| 4
+
| DWORD
+
| The offset to section B. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0060
+
| 4
+
| DWORD
+
| The number of entries in section B.
+
|-
+
|
+
| 0x0064
+
| 4
+
| DWORD
+
| The offset to section C. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0068
+
| 4
+
| DWORD
+
| Length of section C.
+
|-
+
|
+
| 0x006C
+
| 4
+
| DWORD
+
| Offset to section D. The offset is relative from the start of the file.
+
|-
+
|
+
| 0x0070
+
| 4
+
| DWORD
+
| The number of entries in section D.
+
|-
+
|
+
| 0x0074
+
| 4
+
| DWORD
+
| Length of section D.
+
|-
+
|
+
| 0x0078
+
| 8
+
| ?
+
| Unknown
+
|-
+
|
+
| 0x0080
+
| 8
+
| FILETIME
+
| Latest execution time (or run time) of executable (FILETIME)
+
|-
+
|
+
| <b>0x0088</b>
+
| <b>7 x 8 = 56</b>
+
| <b>FILETIME</b>
+
| <b>Older (most recent) latest execution time (or run time) of executable (FILETIME)</b>
+
|-
+
|
+
| <b>0x00C0</b>
+
| <b>16</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
|
+
| 0x00D0
+
| 4
+
| DWORD
+
| Execution counter (or run count)
+
|-
+
|
+
| <b>0x00D4</b>
+
| <b>4</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
|
+
| <b>0x00D8</b>
+
| <b>4</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
|
+
| <b>0x00DC</b>
+
| <b>88</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
|}
+
  
== Section A - Metrics array ==
+
<pre>
This section contains an array with 20 byte (version 17) or 32 byte (version 23 and 26) metrics array entry records.
+
def ssca_xp_hash_function(filename):
 +
    hash_value = 0
 +
    for character in filename:
 +
        hash_value = ((hash_value * 37) + ord(character)) % 0x100000000
 +
        hash_value = (hash_value * 314159269) % 0x100000000
 +
        if hash_value > 0x80000000:
 +
            hash_value = 0x100000000 - hash_value
  
A metrics entry records consists of:
+
    return (abs(hash_value) % 1000000007) % 0x100000000
{| class="wikitable"
+
</pre>
|-
+
! Field
+
! Offset
+
! Length
+
! Type
+
! Notes
+
|-
+
|
+
| 0
+
| 4
+
| DWORD
+
| Start time in ms
+
|-
+
|
+
| 4
+
| 4
+
| DWORD
+
| Duration in ms
+
|-
+
|
+
| 8
+
| 4
+
| DWORD
+
| Average duration in ms?
+
|-
+
|
+
| 12
+
| 4
+
| DWORD
+
| Filename string offset <br> The offset is relative to the start of the filename string section (section C)
+
|-
+
|
+
| 16
+
| 4
+
| DWORD
+
| Filename string number of characters without end-of-string character
+
|-
+
|
+
| 20
+
| 4
+
| DWORD
+
| Unknown, flags?
+
|-
+
|
+
| 24
+
| 8
+
|
+
| NTFS file reference
+
|}
+
  
== Section B - Trace chains array ==
+
=== SCCA Vista hash function ===
This section contains an array with 12 byte (version 17, 23 and 26) entry records.
+
A Python implementation of the SCCA Vista hash function:
  
{| class="wikitable"
+
<pre>
|-
+
def ssca_vista_hash_function(filename):
! Field
+
    hash_value = 314159
! Offset
+
    for character in filename:
! Length
+
        hash_value = ((hash_value * 37) + ord(character)) % 0x100000000
! Type
+
    return hash_value
! Notes
+
</pre>
|-
+
|
+
| 0
+
| 4
+
|
+
| Next array entry index <br> Contains the next trace chain array entry index in the chain, where the first entry index starts with 0, or -1 (0xffffffff) for the end-of-chain.
+
|-
+
|
+
| 4
+
| 4
+
|
+
| Total block load count <br> Number of blocks loaded (or fetched) <br> The block size 512k (512 x 1024) bytes
+
|-
+
|
+
| 8
+
| 1
+
|
+
| Unknown
+
|-
+
|
+
| 9
+
| 1
+
|
+
| Sample duration in ms?
+
|-
+
|
+
| 10
+
| 2
+
|
+
| Unknown
+
|}
+
  
== Section C - Filename strings ==
+
=== SCCA 2008 hash function ===
This section contains filenames strings, it consists of an array of UTF-16 little-endian formatted strings with end-of-string characters (U+0000).
+
A Python implementation of the SCCA 2008 hash function:
  
At the end of the section there seems to be alignment padding that can contain remnant values.
+
<pre>
 +
def ssca_2008_hash_function(filename):
 +
    hash_value = 314159
 +
    filename_index = 0
 +
    filename_length = len(filename)
 +
    while filename_index + 8 < filename_length:
 +
        character_value = ord(filename[filename_index + 1]) * 37
 +
        character_value += ord(filename[filename_index + 2])
 +
        character_value *= 37
 +
        character_value += ord(filename[filename_index + 3])
 +
        character_value *= 37
 +
        character_value += ord(filename[filename_index + 4])
 +
        character_value *= 37
 +
        character_value += ord(filename[filename_index + 5])
 +
        character_value *= 37
 +
        character_value += ord(filename[filename_index + 6])
 +
        character_value *= 37
 +
        character_value += ord(filename[filename_index]) * 442596621
 +
        character_value += ord(filename[filename_index + 7])
 +
        hash_value = ((character_value - (hash_value * 803794207)) % 0x100000000)
 +
        filename_index += 8
  
== Section D - Volumes information (block) ==
+
    while filename_index < filename_length:
 +
      hash_value = (((37 * hash_value) + ord(filename[filename_index])) % 0x100000000)
 +
      filename_index += 1
  
Section D contains one or more subsections, each subsection refers to directories on a volume.
+
    return hash_value
 +
</pre>
  
If all the executables and libraries referenced in the C section are from one single disk volume, there will be only one section in the D section. If multiple volumes are referenced by section C, section D will contain multiple sections.  (A simple way to force this situation is to copy, say, NOTEPAD.EXE to a USB drive, and start it from that volume. The corresponding prefetch file will have one D header referring to, e.g. \DEVICE\HARDDISK1\DP(1)0-0+4 (the USB drive), and one to, e.g. \DEVICE\HARDDISKVOLUME1\ (where the .DLLs and other support files were found).
+
== Registry Keys ==
 +
<pre>
 +
Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters
 +
</pre>
  
In this section, all offsets are assumed to be counted from the start of the D section.
+
The EnablePrefetcher Registry value can be used to disable prefetch.
  
=== Volume information ===
+
== See Also ==
The structure of the volume information is version dependent.
+
* [[Prefetch XML]]
 +
* [[ReadyBoot]]
 +
* [[SuperFetch]]
 +
* [[Windows]]
 +
* [[Windows Prefetch File Format]]
  
==== Volume information - version 17 ====
+
== External Links ==
The volume information – version 17 is 40 bytes in size and consists of:
+
* [http://msdn.microsoft.com/msdnmag/issues/01/12/XPKernel/default.aspx More detail from Microsoft]
 +
* [http://en.wikipedia.org/wiki/Prefetcher Wikipedia Prefetcher]
 +
* [http://msdn.microsoft.com/en-us/library/ms940847(v=winembedded.5).aspx MSDN: Disabling Prefetch]
 +
* [http://www.microsoft.com/whdc/driver/kernel/XP_kernel.mspx Kernel Enhancements for Windows XP], by [[Microsoft]], January 13, 2003 (Microsoft's description of Prefetch when Windows XP was introduced)
 +
* [http://blogs.msdn.com/b/ryanmy/archive/2005/05/25/421882.aspx Misinformation and the The Prefetch Flag], MSDN Blogs, May 25, 2005
 +
* [http://windowsir.blogspot.ch/2005/07/prefetch-file-metadata.html Prefetch file metadata], by [[Harlan Carvey]], July 13, 2005
 +
* [http://windowsir.blogspot.ch/2006/04/prefetch-files-revisited.html Prefetch files, revisited], by [[Harlan Carvey]], April 13, 2006
 +
* [http://blogs.msdn.com/b/e7/archive/2009/05/05/support-and-q-a-for-solid-state-drives-and.aspx Support and Q&A for Solid-State Drives], by Steven Sinofsky, May 5, 2009
 +
* [http://computer-forensics.sans.org/blog/2009/08/05/de-mystifying-defrag-identifying-when-defrag-has-been-used-for-anti-forensics-part-1-windows-xp/ De-mystifying Defrag: Identifying When Defrag Has Been Used for Anti-Forensics (Part 1 - Windows XP)], by [[Chad Tilbury]], August 5, 2009
 +
* [http://www.swiftforensics.com/2010/04/the-windows-prefetchfile.html Windows Prefetch File (old blog entry from 42 LLC)], by [[Yogesh Khatri]], April 14, 2010
 +
* [http://msdn.microsoft.com/en-us/library/windows/hardware/dn653317(v=vs.85).aspx Windows PC Accelerators], by Microsoft, October 8, 2010
 +
* [http://www.dfinews.com/articles/2010/12/decoding-prefetch-files-forensic-purposes-part-1 Decoding Prefetch Files for Forensic Purposes: Part 1], by [[Mark Wade]], December 8, 2010
 +
* [http://crucialsecurityblog.harris.com/2011/04/11/prefetch-files-at-face-value/ Prefetch Files at Face Value], by [[Mark Wade]], April 11, 2011
 +
* [http://kitrap08.blogspot.hk/2011/07/windows-logical-prefetcher.html Windows Logical Prefetcher], TTS blog, July 30, 2011 (article is in Russian)
 +
* [http://labit.in/pliki-prefetch-w-windows/ Prefetch i niedokładny licznik] by Paweł Hałdrzyński, August 20, 2011 (article in Polish; uncertain about the year of publication)
 +
* [http://windowsir.blogspot.ch/2012/03/prefetch-analysis-revisited.html Prefetch Analysis, Revisited], by [[Harlan Carvey]], March 8, 2012
 +
* [http://windowsir.blogspot.ch/2012/03/prefetch-analysis-revisitedagain.html Prefetch Analysis, Revisited...Again...], by [[Harlan Carvey]], March 15, 2012
 +
* [http://www.hexacorn.com/blog/2012/06/13/prefetch-hash-calculator-a-hash-lookup-table-xpvistaw7w2k3w2k8/ Prefetch Hash Calculator + a hash lookup table xp/vista/w7/w2k3/w2k8], Hexacorn blog, June 13, 2012
 +
* [http://www.hexacorn.com/blog/2012/10/29/prefetch-file-names-and-unc-paths/ Prefetch file names and UNC paths], Hexacorn blog, October 29, 2012
 +
* [http://journeyintoir.blogspot.ch/2012/12/ntosboot-prefetch-file.html NTOSBOOT Prefetch File], by [[Corey Harrell]], December 5, 2012
 +
* [http://www.invoke-ir.com/2013/09/whats-new-in-prefetch-for-windows-8.html What's New in the Prefetch for Windows 8??], by Jared Atkinson, September 21, 2013
 +
* [http://www.swiftforensics.com/2013/10/windows-prefetch-pf-files.html?m=1 Windows Prefetch (.PF) files], by [[Yogesh Khatri]], October 21, 2013
 +
* [http://resources.infosecinstitute.com/windows-systems-artifacts-digital-forensics-part-iii-prefetch-files/ Windows Systems and Artifacts in Digital Forensics: Part III: Prefetch Files], by Ivan Dimov, November 21, 2013
 +
* [http://i.imgur.com/riuljsK.jpg Prefetch 101 - a Windows 8 Prefetch file walkthrough], by Jared Atkinson, 2014
  
{| class="wikitable"
+
== Tools ==
|-
+
! Field
+
! Offset
+
! Length
+
! Type
+
! Notes
+
|-
+
| VI1
+
| +0x0000
+
| 4
+
| DWORD
+
| Offset to volume device path (Unicode, terminated by U+0000)
+
|-
+
| VI2
+
| +0x0004
+
| 4
+
| DWORD
+
| Length of volume device path (nr of characters, including terminating U+0000)
+
|-
+
| VI3
+
| +0x0008
+
| 8
+
| FILETIME
+
| Volume creation time.
+
|-
+
| VI4
+
| +0x0010
+
| 4
+
| DWORD
+
| Volume serial number of volume indicated by volume string
+
|-
+
| VI5
+
| +0x0014
+
| 4
+
| DWORD
+
| Offset to sub section E
+
|-
+
| VI6
+
| +0x0018
+
| 4
+
| DWORD
+
| Length of sub section E (in bytes)
+
|-
+
| VI7
+
| +0x001C
+
| 4
+
| DWORD
+
| Offset to sub section F
+
|-
+
| VI8
+
| +0x0020
+
| 4
+
| DWORD
+
| Number of strings in sub section F
+
|-
+
| VI9
+
| +0x0024
+
| 4
+
| ?
+
| Unknown
+
|-
+
|}
+
  
==== Volume information - version 23 ====
+
=== Commercial ===
The volume information entry – version 23 is 104 bytes in size and consists of:
+
  
{| class="wikitable"
+
=== Free - Non Open Source ===
|-
+
* [http://www.woanware.co.uk/forensics/prefetchforensics.html PrefetchForensics], PrefetchForensics is an application to extract information from Windows Prefetch files
! Field
+
* [http://redwolfcomputerforensics.com/index.php?option=com_content&task=view&id=42&Itemid=55 Prefetch-Parser], Parse the prefetch files and display information
! Offset
+
* [http://www.mitec.cz/wfa.html Windows File Analyzer] - Parses Prefetch files, thumbnail databases, shortcuts, index.dat files, and the recycle bin
! Length
+
* [http://www.tzworks.net/prototype_page.php?proto_id=1 Windows Prefetch Parser (pf)], Free tool that can be run on Windows, Linux or Mac OS-X
! Type
+
! Notes
+
|-
+
| VI1
+
| +0x0000
+
| 4
+
| DWORD
+
| Offset to volume device path (Unicode, terminated by U+0000)
+
|-
+
| VI2
+
| +0x0004
+
| 4
+
| DWORD
+
| Length of volume device path (nr of characters, including terminating U+0000)
+
|-
+
| VI3
+
| +0x0008
+
| 8
+
| FILETIME
+
| Volume creation time.
+
|-
+
| VI4
+
| +0x0010
+
| 4
+
| DWORD
+
| Volume serial number of volume indicated by volume string
+
|-
+
| VI5
+
| +0x0014
+
| 4
+
| DWORD
+
| Offset to sub section E
+
|-
+
| VI6
+
| +0x0018
+
| 4
+
| DWORD
+
| Length of sub section E (in bytes)
+
|-
+
| VI7
+
| +0x001C
+
| 4
+
| DWORD
+
| Offset to sub section F
+
|-
+
| VI8
+
| +0x0020
+
| 4
+
| DWORD
+
| Number of strings in sub section F
+
|-
+
| VI9
+
| +0x0024
+
| 4
+
| ?
+
| Unknown
+
|-
+
| <b>VI10</b>
+
| <b>+0x0028</b>
+
| <b>28</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
| <b>VI11</b>
+
| <b>+0x0044</b>
+
| <b>4</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
| <b>VI12</b>
+
| <b>+0x0048</b>
+
| <b>28</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
| <b>VI13</b>
+
| <b>+0x0064</b>
+
| <b>4</b>
+
| <b>?</b>
+
| <b>Unknown</b>
+
|-
+
|}
+
  
==== Volume information - version 26 ====
+
=== Open Source ===
The volume information entry – version 26 appears to be similar to volume information – version 23.
+
* [https://code.google.com/p/prefetch-tool/ prefetch-tool], Script to extract information from windows prefetch folder
 
+
* [http://bitbucket.cassidiancybersecurity.com/prefetch-parser prefetch-parser], Standalone Python tools that parses Windows prefetch files and extracts all known and forensically relevant artefacts contained.
=== Sub section E - NTFS file references ===
+
* [[plaso]]
This sub section can contain NTFS file references.
+
 
+
For more information see [https://googledrive.com/host/0B3fBvzttpiiSbl9XZGZzQ05hZkU/Windows%20Prefetch%20File%20(PF)%20format.pdf Windows Prefetch File (PF) format].
+
 
+
=== Sub section F - Directory strings ===
+
This sub sections contains directory strings. The number of strings is stored in the volume information.
+
 
+
A directory string is stored in the following structure:
+
{| class="wikitable"
+
|-
+
! Field
+
! Offset
+
! Length
+
! Type
+
! Notes
+
|-
+
|
+
| 0x0000
+
| 2
+
| DWORD
+
| Number of characters (WORDs) of the directory name. The value does not include the end-of-string character.
+
|-
+
|
+
| 0x0002
+
|
+
| USTR
+
| The directory name as a Unicode (UTF-16 litte-endian string) terminated by an end-of-string character (U+0000).
+
|-
+
|}
+
 
+
== See Also ==
+
* [[Prefetch]]
+
 
+
== External Links ==
+
* [https://googledrive.com/host/0B3fBvzttpiiSbl9XZGZzQ05hZkU/Windows%20Prefetch%20File%20(PF)%20format.pdf Windows Prefetch File (PF) format], by the [[libssca|libssca project]]
+
* [http://bitbucket.cassidiancybersecurity.com/prefetch-parser/wiki/Home Windows Prefetch file format], by the [http://bitbucket.cassidiancybersecurity.com/prefetch-parser prefetch-parser] project.
+
  
[[Category:File Formats]]
+
[[Category:Windows]]

Revision as of 23:02, 22 June 2014

Information icon.png

Please help to improve this article by expanding it.
Further information might be found on the discussion page.

Windows Prefetch files, introduced in Windows XP, are designed to speed up the application startup process. Prefetch files contain the name of the executable, a Unicode list of DLLs used by that executable, a count of how many times the executable has been run, and a timestamp indicating the last time the program was run. Although Prefetch is present in Windows 2003, by default it is only enabled for boot prefetching. The feature is also found in Windows Vista, where it has been augmented with SuperFetch, ReadyBoot, and ReadyBoost.

From [1]:

  • SuperFetch; analyzes per-machine usage patterns over time and optimizes the data that is kept in memory.
  • ReadyBoot; decreases boot time (the time from turning power on to reaching the log-on screen) by preloading the files and startup programs needed per-machine into a cache.
  • ReadyBoost; supports the use of flash storage devices like Universal Serial Bus (USB) flash drives and Secure Digital (SD) flash cards to boost PC performance.
  • ReadyDrive; supports hybrid hard disk drives.

For SSD drives Prefetch is disabled by default [2].

Prefetch files

The Prefetch files are stored in the directory:

%SystemRoot%\Prefetch

The following files can be found in the Prefetch directory:

  • *.pf, which are Prefetch files;
  • Ag*.db and Ag*.db.trx, which are SuperFetch files;
  • Layout.ini;
  • PfPre_*.db;
  • PfSvPerfStats.bin

A Prefetch file contains the name of the application, a dash, and then an eight character hash of the location from which that application was run, and a .pf extension. The filenames should be all uppercase except for the extension. E.g. a filename for md5deep would look like: MD5DEEP.EXE-4F89AB0C.pf. If an application is run from two different locations on the drive (i.e. the user runs C:\md5deep.exe and then C:\Apps\Hashing\md5deep.exe), there will be two different prefetch files in the Prefetch folder. According to MSDN up to 128 Prefetch files can be stored in the Prefetch directory [3].

File format

Each Prefetch file has a 4-byte signature (at offset 4) "SCCA" (or in hexadecimal notation 0x53 0x43 0x43 0x41). The signature is assumed to be preceded by a 4-byte format version indicator:

For more information about the file format see: Windows Prefetch File Format

Metadata

The Prefetch file contains various metadata.

  • The executable's name, up to 29 characters.
  • The run count, or number of times the application has been run.
  • Volume related information, like volume path and volume serial number.
  • The size of the Prefetch file (sometimes referred to as end of file (EOF)).
  • The files and directories that were used doing the application's start-up.

Timestamps

The Prefetch file contains 2 types of timestamps

  • The time when the application was last ran (executed). Version 26 of the Prefetch format maintains 7 previous last run times.
  • The volume creation time (part of the volume information) of the volume the Prefetch file was created on.

The file system creation time of the Prefetch file indicates the first time the application was executed. Both the file system modification time of the Prefetch file and the embedded last run time indicate the last time the application was executed.

Prefetch hash

There are multiple known hashing functions to be used for prefetch file filename hashing, namely:

  • SCCA XP hash function; used on Windows XP and Windows 2003
  • SCCA Vista hash function; used on Windows Vista
  • SCCA 2008 hash function; used on Windows 2008, Windows 7, (possibly: Windows 2012) and Windows 8 (including 8.1)

SCCA XP hash function

A Python implementation of the SCCA XP hash function:

def ssca_xp_hash_function(filename):
    hash_value = 0
    for character in filename:
        hash_value = ((hash_value * 37) + ord(character)) % 0x100000000
        hash_value = (hash_value * 314159269) % 0x100000000
        if hash_value > 0x80000000:
            hash_value = 0x100000000 - hash_value

    return (abs(hash_value) % 1000000007) % 0x100000000

SCCA Vista hash function

A Python implementation of the SCCA Vista hash function:

def ssca_vista_hash_function(filename):
    hash_value = 314159
    for character in filename:
        hash_value = ((hash_value * 37) + ord(character)) % 0x100000000
    return hash_value

SCCA 2008 hash function

A Python implementation of the SCCA 2008 hash function:

def ssca_2008_hash_function(filename):
    hash_value = 314159
    filename_index = 0
    filename_length = len(filename)
    while filename_index + 8 < filename_length:
        character_value = ord(filename[filename_index + 1]) * 37
        character_value += ord(filename[filename_index + 2])
        character_value *= 37
        character_value += ord(filename[filename_index + 3])
        character_value *= 37
        character_value += ord(filename[filename_index + 4])
        character_value *= 37
        character_value += ord(filename[filename_index + 5])
        character_value *= 37
        character_value += ord(filename[filename_index + 6])
        character_value *= 37
        character_value += ord(filename[filename_index]) * 442596621
        character_value += ord(filename[filename_index + 7])
        hash_value = ((character_value - (hash_value * 803794207)) % 0x100000000)
        filename_index += 8

    while filename_index < filename_length: 
       hash_value = (((37 * hash_value) + ord(filename[filename_index])) % 0x100000000)
       filename_index += 1

    return hash_value 

Registry Keys

Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters

The EnablePrefetcher Registry value can be used to disable prefetch.

See Also

External Links

Tools

Commercial

Free - Non Open Source

Open Source

  • prefetch-tool, Script to extract information from windows prefetch folder
  • prefetch-parser, Standalone Python tools that parses Windows prefetch files and extracts all known and forensically relevant artefacts contained.
  • plaso