Difference between revisions of "Prefetch"

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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:

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 8.1 (note this could be Windows 8 as well but has not been confirmed)

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.

External Links

More detail from Microsoft
Wikipedia Prefetcher
MSDN: Disabling Prefetch
Windows XP: Kernel Improvements Create a More Robust, Powerful, and Scalable OS, by Mark Russinovich, David Solomon, December 2001
Kernel Enhancements for Windows XP, by Microsoft, January 13, 2003 (Microsoft's description of Prefetch when Windows XP was introduced)
Misinformation and the The Prefetch Flag, MSDN Blogs, May 25, 2005
Prefetch file metadata, by Harlan Carvey, July 13, 2005
Prefetch files, revisited, by Harlan Carvey, April 13, 2006
Windows Memory Management, by logicchild, September 17, 2008
Windows Memory Management - Part 2, by logicchild, September 25, 2008
Support and Q&A for Solid-State Drives, by Steven Sinofsky, May 5, 2009
De-mystifying Defrag: Identifying When Defrag Has Been Used for Anti-Forensics (Part 1 - Windows XP), by Chad Tilbury, August 5, 2009
Windows Prefetch File (old blog entry from 42 LLC), by Yogesh Khatri, April 14, 2010
Windows PC Accelerators, by Microsoft, October 8, 2010
Decoding Prefetch Files for Forensic Purposes: Part 1, by Mark Wade, December 8, 2010
Prefetch Files at Face Value, by Mark Wade, April 11, 2011
Windows Logical Prefetcher, TTS blog, July 30, 2011 (article is in Russian)
Prefetch i niedokładny licznik by Paweł Hałdrzyński, August 20, 2011 (article in Polish; uncertain about the year of publication)
Prefetch Analysis, Revisited, by Harlan Carvey, March 8, 2012
Prefetch Analysis, Revisited...Again..., by Harlan Carvey, March 15, 2012
Prefetch Hash Calculator + a hash lookup table xp/vista/w7/w2k3/w2k8, Hexacorn blog, June 13, 2012
Prefetch file names and UNC paths, Hexacorn blog, October 29, 2012
NTOSBOOT Prefetch File, by Corey Harrell, December 5, 2012
What's New in the Prefetch for Windows 8??, by Jared Atkinson, September 21, 2013
Windows Prefetch (.PF) files, by Yogesh Khatri, October 21, 2013
Windows Systems and Artifacts in Digital Forensics: Part III: Prefetch Files, by Ivan Dimov, November 21, 2013
Prefetch 101 - a Windows 8 Prefetch file walkthrough, by Jared Atkinson, 2014

Tools

Commercial

Free - Non Open Source

PrefetchForensics, PrefetchForensics is an application to extract information from Windows Prefetch files
Prefetch-Parser, Parse the prefetch files and display information
Windows File Analyzer - Parses Prefetch files, thumbnail databases, shortcuts, index.dat files, and the recycle bin
Windows Prefetch Parser (pf), Free tool that can be run on Windows, Linux or Mac OS-X

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

@@ Line 1: / Line 1: @@
 {{Expand}}
-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]]. 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].
+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]].
-Up to 128 Prefetch files are stored in the <tt>%SystemRoot%\Prefetch</tt> directory [http://blogs.msdn.com/ryanmy/archive/2005/05/25/421882.aspx]. Each file in that directory should contain 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. The format of hashes is not known. A sample 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.
+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.
+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].
-== File format ==
+== Prefetch files ==
+The Prefetch files are stored in the directory:
+<pre>
+%SystemRoot%\Prefetch
+</pre>
+The following files can be found in the Prefetch directory:
+* <tt>*.pf</tt>, which are Prefetch files;
+* <tt>Ag*.db</tt> and <tt>Ag*.db.trx</tt>, which are [[SuperFetch]] files;
+* <tt>Layout.ini</tt>;
+* <tt>PfPre_*.db</tt>;
+* <tt>PfSvPerfStats.bin</tt>
+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].
+=== 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]]
@@ Line 12: / Line 32: @@
 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 ==
@@ Line 76: / Line 111: @@
      return hash_value
 </pre>
-== Timestamps ==
-Both the [[NTFS]] timestamps for a Prefetch file and the timestamp embedded in each Prefetch file contain valuable information. The timestamp embedded within the Prefetch file is a 64-bit (QWORD) [http://msdn2.microsoft.com/en-us/library/ms724284.aspx FILETIME] object The creation date of the file indicates the first time the application was executed. Both the modification date of the file and the embedded timestamp indicate the last time the application was executed.
-Windows will store timestamps according to a Windows [http://msdn.microsoft.com/en-us/library/ms724290%28VS.85%29.aspx file time].
-==== Creation Time ====
-The creation time does not have a static offset on any Windows platform. The location of the creation time can be found using the offset 0x8 + length of Volume path offset. See section Volume for more information.
-==== Last Run Time ====
-A timestamp of when the application was last ran is embedded into the Prefetch file.
-The offset from the beginning of the file to the "Last Run Time" is located:
-* at offset 0x78 on Windows XP and Windows 2003.
-* at offset 0x80 on Windows Vista, Windows 7, and Windows 8 (up to 8 entries for Windows 8).
-== Other MetaData ==
-The Prefetch file contains various other 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.
 == Registry Keys ==
@@ Line 108: / Line 120: @@
 == See Also ==
-* [[Windows Prefetch File Format]]
-* [[SuperFetch]]
 * [[Prefetch XML]]
+* [[ReadyBoot]]
+* [[SuperFetch]]
 * [[Windows]]
+* [[Windows Prefetch File Format]]
 == External Links ==
@@ Line 117: / Line 130: @@
 * [http://en.wikipedia.org/wiki/Prefetcher Wikipedia Prefetcher]
 * [http://msdn.microsoft.com/en-us/library/ms940847(v=winembedded.5).aspx MSDN: Disabling Prefetch]
+* [http://msdn.microsoft.com/en-us/magazine/cc302206.aspx Windows XP: Kernel Improvements Create a More Robust, Powerful, and Scalable OS], by [[Mark Russinovich]], [[David Solomon]], December 2001
 * [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://www.codeproject.com/Articles/29449/Windows-Memory-Management Windows Memory Management], by logicchild, September 17, 2008
+* [http://www.codeproject.com/Articles/29692/Windows-Memory-Management-Part Windows Memory Management - Part 2], by logicchild, September 25, 2008
 * [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
@@ Line 135: / Line 152: @@
 * [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
 == Tools ==
@@ Line 148: / Line 167: @@
 === Open Source ===
 * [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.
+* [[plaso]]
+[[Category:Windows]]

Difference between revisions of "Prefetch"

Latest revision as of 04:42, 29 June 2014

Contents

Prefetch files

File format

Metadata

Timestamps

Prefetch hash

SCCA XP hash function

SCCA Vista hash function

SCCA 2008 hash function

Registry Keys

See Also

External Links

Tools

Commercial

Free - Non Open Source

Open Source

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