Difference between pages "Encase image file format" and "Pagefile.sys"

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The Encase image file format is used by [[EnCase]] used to store various types of digital evidence e.g.
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Microsoft [[Windows]] uses a '''paging file''', called <tt>pagefile.sys</tt> to store frames of memory that do not current fit into [[physical memory]]. Although Windows supports up to 16 paging files, in practice normally only one is used. This file, stored in <tt>%SystemDrive%\pagefile.sys</tt> is a hidden system file. Because the operating system keeps this file open during normal operation, it can never be read or accessed by a user. It is possible to read this file by parsing the raw file system (e.g. using [[The Sleuth Kit]]).
* disk image (physical bitstream of an acquired disk)
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* volume image
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* memory
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* logical files
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== History ==
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== Analysis Options ==
Expert Witness (for Windows) was the original name for EnCase (dating back to 1998). More info about this can be found on the Internet Archive [http://web.archive.org/web/19980504153628/http://guidancesoftware.com/] including a demo of the original software [http://web.archive.org/web/19980504153759/http://guidancesoftware.com/data/ewsetup.exe].
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(presumably) the product was renamed because it intruded the Expert Wittness trademark held by ASR Data [http://www.asrdata.com/wp-content/themes/asr/pdf/ruling.pdf].
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Data is stored in the paging file when Windows determines that it needs more space in physical memory. Because storage locations in the paging file are not necessarily sequential, it is unlikely to find consecutive pages there. Although it is possible to find data in chunks smaller than or equal to 4KB, its the largest an examiner can hope for.  
  
The Encase image file format therefore is also referred to as the Expert Witness (Compression) Format.
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Sadly, the most productive method to date for analyzing paging files is searching for [[strings]]. It is possible to [[Carving|carve out files]], but as noted the examiner is unlikely to find anything larger than 4KB.
 
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Currently there are 2 versions of the format:
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* version 1 is (reportedly) based on [[:File:ASR Data's Expert Witness Compression Format.pdf|ASR Data's Expert Witness Compression Format]]
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* version 2 was introduced in EnCase 7, for which a format specification (at least non-encrypted Ex01) is available, but requires registration.
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The libewf project indicates that the January 2012 version of the version 2 format specification, besides Lx01 not being specified, is sufficient to read non-encrypted Ex01 files.
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Although the format specification is not complete, at the moment Guidance Software is working on an update. This will not include:
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* encrypted Ex01
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* Lx01
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So in contrast to other claims [http://tech.groups.yahoo.com/group/linux_forensics/message/3555] the EWF file format is:
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* proprietary
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* partially open specification
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For more information about these definitions see: [[File formats]]
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== Version 1 ==
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The media data can be stored in multiple evidence files, which are called segment files.
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Each segment file consist of multiple sections, which has a distinct section start definition containing a section type.
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Up to EnCase 5 the segment file were limited to 2 GiB, due to the internal 31-bit file offset representation. This limitation was lifted by adding a base offset value in EnCase 6.
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EnCase allows to store the data compressed either using a fast or best level of the deflate compression method.
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EnCase 7 no longer distinguishes between fast or best compression and just provides for either uncompressed or compressed.
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Besides digital evidence the evidence files, or segment files, contain a header containing case information.
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The case information which entails date and time of acquisition, an examiner's name, notes on the acquisition, and an optional password.
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* In EnCase 3 the case information header is stored in the "header" section, which is defined twice within the file and contain the same information.
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* As of EnCase 4 an additional "header2" section was added. The "header" section now appears only once, but the new "header2" section twice.
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The format adds error detection by storing the data with checksums (Adler32), for both the metadata as the data blocks, which are by default 64 x 512 byte sectors (32 KiB).
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As of EnCase 5 the number of sectors per block (chunk) can vary.
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EnCase 3F introduced an "error2" section that it uses to record the location and number of bad sector chunks. The way it handles the sections it can't read is that those areas are filled with zero.
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Then EnCase displays to the user the areas that could not be read when the image was acquired. The granularity of unreadable chunks appears to be 32K.
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As of EnCase 5 the granularity of unreadable chunks can vary.
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EnCase 3 can store a one-way hash of the data. For a bitstream it does so by calculating e.g. a MD5 hash of the original media data and adds a hash section to the last of the segment file.
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As of EnCase 6 the option to store a SHA1 hash was added.
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EnCase 5 and later have the option to store '''single files''' into the EnCase Logical Evidence File (LEF) or EWF-L01.
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This format changed slightly in EnCase 6 and 7.
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== Version 2 ==
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In EnCase 7 the EWF format was succeeded by the EnCase Evidence File Format Version 2 (EWF2-EX01 and EWF2-LX01).
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EWF2-EX01 is at it's lower levels a different format then EWF-E01 and provides support for:
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* bzip2 compression
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* direct encryption (AES-256) of the section data
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The same features are added to the new logical evidence file format (EWF2-LX01) with the exception of encryption.
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The actual encryption method and corresponding key derivation are, currently, not open.
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EWF2-EX01, EWF2-LX01 are not backwards compatible with previous EnCase products.
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== See Also ==
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* [[:File:ASR Data's Expert Witness Compression Format.pdf|ASR Data's Expert Witness Compression Format]]
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* [[EnCase]]
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== External Links ==  
 
== External Links ==  
  
* [http://encase-enterprise-blog.guidancesoftware.com/2012/01/2nd-generation-encase-evidence-file.html 2nd Generation EnCase Evidence File Technical Specification now Available], Guidance Software, Jan 2012
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* [[Nicholas Maclean]] published his thesis on [[Windows Memory Analysis|Windows memory analysis]] and discussed the paging file. Unfortunately the document does not appear to be online anymore.
* Requires registration: [http://www.guidancesoftware.com/DocumentRegistration.aspx?did=1000018246 EnCase Evidence File Format Version 2], Guidance Software, Jan 2012
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* ''[http://www.jessekornblum.com/research/papers/buffalo.pdf Using Every Part of the Buffalo in Windows Memory Analysis]'' - A paper discussing the different states of memory including where to find data in the paging file
* [http://code.google.com/p/libewf/downloads/detail?name=Expert%20Witness%20Compression%20Format%20%28EWF%29.pdf Expert Witness Compression Format (EWF)].
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* ''[http://www.microsoft.com/MSPress/books/6710.aspx Microsoft Windows Internals]'' - An excellent guide to the inner workings of Microsoft Windows
* [http://code.google.com/p/libewf/downloads/detail?name=Expert%20Witness%20Compression%20Format%202%20%28EWF2%29.pdf Expert Witness Compression Format (EWF) version 2].
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* [http://www.cfreds.nist.gov/v2/Basic_Mac_Image.html Sample image in EnCase, iLook, and dd format] - From the [[Computer Forensic Reference Data Sets]] Project
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[[Category:Forensics File Formats]]
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Revision as of 07:09, 8 April 2007

Microsoft Windows uses a paging file, called pagefile.sys to store frames of memory that do not current fit into physical memory. Although Windows supports up to 16 paging files, in practice normally only one is used. This file, stored in %SystemDrive%\pagefile.sys is a hidden system file. Because the operating system keeps this file open during normal operation, it can never be read or accessed by a user. It is possible to read this file by parsing the raw file system (e.g. using The Sleuth Kit).

Analysis Options

Data is stored in the paging file when Windows determines that it needs more space in physical memory. Because storage locations in the paging file are not necessarily sequential, it is unlikely to find consecutive pages there. Although it is possible to find data in chunks smaller than or equal to 4KB, its the largest an examiner can hope for.

Sadly, the most productive method to date for analyzing paging files is searching for strings. It is possible to carve out files, but as noted the examiner is unlikely to find anything larger than 4KB.

External Links