Difference between revisions of "Encase image file format"

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[[EnCase]] uses a closed format for images which is reportedly based on [http://www.asrdata.com/SMART/whitepaper.html ASR Data's Expert Witness Compression Format]. The evidence files, or E01 files, contain a physical bitstream of an acquired disk, prefixed with a '"Case Info" header, interlaced with checksums (Adler32) for every block of 64 x 512 byte sectors (32 KiB), and followed by a footer containing an MD5 hash for the entire bitstream.  Contained in the header are the date and time of acquisition, an examiner's name, notes on the acquisition, and an optional password; the header concludes with its own checksum.
+
The Encase image file format is used by [[EnCase]] used to store various types of digital evidence e.g.
 +
* disk image (physical bitstream of an acquired disk)
 +
* volume image
 +
* memory
 +
* logical files
  
EnCase can store media data into multiple evidence files, which are called segment files. Each segment file consist of multiple sections. Each section consist of a section start definition. This contains a section type.
+
Currently there are 2 versions of the format:
 +
* version 1 is (reportedly) based on [[:File:ASR Data's Expert Witness Compression Format.pdf|ASR Data's Expert Witness Compression Format]].
 +
* version 2 was introduced in EnCase 7, for which a format specification (at least for Ex01) is available, but requires registration.
  
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 using a base offset work around in EnCase 6.
+
The libewf project indicates that the January 2012 version of the version 2 format specification, besides Lx01 not being specified, is sufficient to read the format but not complete.
  
At least from Encase 3 the case info header is contained in the "header" section, which is defined twice within the file and contain the same information.
+
== Version 1 ==
 +
The media data can be stored in multiple evidence files, which are called segment files.
 +
Each segment file consist of multiple sections, which has a distinct section start definition containing a section type.
 +
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.
  
With Encase 4 an additional "header2" section was added. The "header" section now appears only once, but the new "header2" section twice.
 
  
Version 3 of The Encase F introduced an "error2" sections 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. 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.
+
EnCase allows to store the data compressed either using a fast or best level of the deflate compression method.
 +
EnCase 7 no longer distinguishes between fast or best compression and just provides for either uncompressed or compressed.
  
Within Encase 5 the number of sectors per block (chunk) can vary.
 
  
Encase from at least in version 3 can hash the data of the media it acquires.
+
Besides digital evidence the evidence files, or segment files, contain a header containing case information.
It does this by calculating a MD5 hash of the original media data and adds a hash section
+
The case information which entails date and time of acquisition, an examiner's name, notes on the acquisition, and an optional password.
to the last of the segment files. Later versions of Encase 6 also include a SHA1 hash.
+
* 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.
 +
* As of EnCase 4 an additional "header2" section was added. The "header" section now appears only once, but the new "header2" section twice.
  
In EnCase 7 the EWF format was succeeded by the EnCase Evidence File Format Version 2 (EWF-EX01 and EWF-LX01). EnCase 7 also uses a different version of EWF-L01 then its version 6 predecessors.
 
  
EWF-EX01 is at it's lower levels a different format then EWF-E01 and provides support for:
+
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).
* bzip compression
+
As of EnCase 5 the number of sectors per block (chunk) can vary.
* direct encryption (AES-256) of the data
+
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.
 +
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.
 +
As of EnCase 5 the granularity of unreadable chunks can vary.
  
The same features are added to the new logical evidence file format (Lx01) with the exception of encryption.
 
  
EWF-EX01, EWF-LX01 are not backwards compatible with previous EnCase products.  
+
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.
 +
As of EnCase 6 the option to store a SHA1 hash was added.
 +
 
 +
 
 +
EnCase 5 and later have the option to store '''single files''' into the EnCase Logical Evidence File (LEF) or EWF-L01.
 +
This format changed slightly in EnCase 6 and 7.
 +
 
 +
== Version 2 ==
 +
 
 +
In EnCase 7 the EWF format was succeeded by the EnCase Evidence File Format Version 2 (EWF2-EX01 and EWF2-LX01).
 +
EWF2-EX01 is at it's lower levels a different format then EWF-E01 and provides support for:
 +
* bzip2 compression
 +
* direct encryption (AES-256) of the section data
 +
 
 +
The same features are added to the new logical evidence file format (EWF2-LX01) with the exception of encryption.
 +
EWF2-EX01, EWF2-LX01 are not backwards compatible with previous EnCase products.
  
 
== See Also ==
 
== See Also ==
  
[[EnCase]]
+
* [[:File:ASR Data's Expert Witness Compression Format.pdf|ASR Data's Expert Witness Compression Format]]
 +
* [[EnCase]]
  
 
== External Links ==  
 
== External Links ==  
  
* [https://downloads.sourceforge.net/project/libewf/documentation/EWF%20file%20format/Expert%20Witness%20Compression%20Format%20%28EWF%29.pdf Expert Witness Compression Format (EWF)].
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* [http://www.guidancesoftware.com/DocumentRegistration.aspx?did=1000018246 EnCase Evidence File Format Version 2], requires registration
 +
* [http://code.google.com/p/libewf/downloads/detail?name=Expert%20Witness%20Compression%20Format%20%28EWF%29.pdf Expert Witness Compression Format (EWF)].
 +
* [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].
 
* [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
 
* [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
  
 
[[Category:Forensics File Formats]]
 
[[Category:Forensics File Formats]]

Revision as of 01:50, 21 July 2012

The Encase image file format is used by EnCase used to store various types of digital evidence e.g.

  • disk image (physical bitstream of an acquired disk)
  • volume image
  • memory
  • logical files

Currently there are 2 versions of the format:

The libewf project indicates that the January 2012 version of the version 2 format specification, besides Lx01 not being specified, is sufficient to read the format but not complete.

Version 1

The media data can be stored in multiple evidence files, which are called segment files. Each segment file consist of multiple sections, which has a distinct section start definition containing a section type. 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.


EnCase allows to store the data compressed either using a fast or best level of the deflate compression method. EnCase 7 no longer distinguishes between fast or best compression and just provides for either uncompressed or compressed.


Besides digital evidence the evidence files, or segment files, contain a header containing case information. The case information which entails date and time of acquisition, an examiner's name, notes on the acquisition, and an optional password.

  • 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.
  • As of EnCase 4 an additional "header2" section was added. The "header" section now appears only once, but the new "header2" section twice.


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). As of EnCase 5 the number of sectors per block (chunk) can vary. 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. 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. As of EnCase 5 the granularity of unreadable chunks can vary.


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. As of EnCase 6 the option to store a SHA1 hash was added.


EnCase 5 and later have the option to store single files into the EnCase Logical Evidence File (LEF) or EWF-L01. This format changed slightly in EnCase 6 and 7.

Version 2

In EnCase 7 the EWF format was succeeded by the EnCase Evidence File Format Version 2 (EWF2-EX01 and EWF2-LX01). EWF2-EX01 is at it's lower levels a different format then EWF-E01 and provides support for:

  • bzip2 compression
  • direct encryption (AES-256) of the section data

The same features are added to the new logical evidence file format (EWF2-LX01) with the exception of encryption. EWF2-EX01, EWF2-LX01 are not backwards compatible with previous EnCase products.

See Also

External Links