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.
 
  
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.
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The format is (reportedly) based on [http://www.asrdata.com/SMART/whitepaper.html ASR Data's Expert Witness Compression Format].
 +
Currently there are 2 version of the format; version 1 is a closed format and was succeeded by version 2 in EnCase 7, for which a format specification is available, but requires registration.
  
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.
 
  
With Encase 4 an additional "header2" section was added. The "header" section now appears only once, but the new "header2" section twice.
+
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.
  
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.
 
  
Within Encase 5 the number of sectors per block (chunk) can vary.
+
EnCase allow to store the data compressed either using a fast or best level of compression.
 +
EnCase 7 no longer distinguishes between fast or best compression and just offers uncompressed or compressed.
  
Encase from at least in version 3 can hash the data of the media it acquires.
 
It does this by calculating a MD5 hash of the original media data and adds a hash section
 
to the last of the segment files.
 
  
Later versions of Encase 6 included the option to store a MD5 and/or SHA1 hash.
+
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.
  
In EnCase 7 the EWF format was succeeded by the EnCase Evidence File Format Version 2 (EWF-EX01 and EWF-LX01).
 
Guidance has made a specification of the EWF-EX01 format public.
 
  
EnCase 7 also uses a different version of EWF-L01 then its predecessors and no longer distinguishes between fast or best compression.
+
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.
  
EWF-EX01 is at it's lower levels a different format then EWF-E01 and provides support for:
+
 
 +
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.
 +
 
 +
 
 +
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:
 
* bzip compression
 
* bzip compression
 
* direct encryption (AES-256) of the data
 
* direct encryption (AES-256) of the data
  
The same features are added to the new logical evidence file format (Lx01) with the exception of encryption.
+
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.
EWF-EX01, EWF-LX01 are not backwards compatible with previous EnCase products.
+
  
 
== See Also ==
 
== See Also ==
Line 38: Line 54:
 
== 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)].
+
* [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
 +
* [http://www.guidancesoftware.com/DocumentRegistration.aspx?did=1000018246 EnCase Evidence File Format Version 2], requires registration
  
 
[[Category:Forensics File Formats]]
 
[[Category:Forensics File Formats]]

Revision as of 23:46, 4 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


The format is (reportedly) based on ASR Data's Expert Witness Compression Format. Currently there are 2 version of the format; version 1 is a closed format and was succeeded by version 2 in EnCase 7, for which a format specification is available, but requires registration.


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 allow to store the data compressed either using a fast or best level of compression. EnCase 7 no longer distinguishes between fast or best compression and just offers 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.


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:

  • bzip compression
  • direct encryption (AES-256) of the 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

EnCase

External Links