Difference between pages "Microsoft Windows Mobile" and "Disk Imaging"

From ForensicsWiki
(Difference between pages)
Jump to: navigation, search
(Added some more data acquired from the PocketPC wiki.)
 
(Decryption while imaging)
 
Line 1: Line 1:
=Windows Mobile Versions=
+
{{expand}}
==Windows Mobile 2002==
+
Windows Mobile 2002 is powered by Windows CE 3.0.  It was targeted at QVGA Pocket PCs.
+
  
==Windows Mobile 2003==
+
Disk imaging is the process of making a bit-by-bit copy of a disk. Imaging (in more general terms) can apply to anything that can be considered as a bit-stream, e.g. a physical or logical volumes, network streams, etc.
Windows Mobile 2003, codenamed "Ozone", was released on June 23, 2003.  It came in three different editions; Windows Mobile 2003 for Pocket PC, Windows Mobile 2003 for Pocket PC Phone Edition, and Windows Mobile 2003 for Smartphone.  The Pocket PC and Pocket PC Phone Edition are very similar other then the fact that the Pocket PC Phone Edition was designed for Pocket PCs with added fun functionalities.  This version of Windows Mobile is powered by Windows CE 4.20, which claimed to provide a more responsive system when compared with devices running Windows CE 3.0.
+
  
This version of the operating system added many useful features, including a picture viewer, built-in Bluetooth and WiFi support, Windows Media Player 9.0, as well as a host of Personal Information Management application improvements. This version of Windows Mobile required ActiveSync 3.7 to communicate with a host computer.
+
The most straight-forward disk imaging method is reading a disk from start to end and writing the data to a [[:Category:Forensics_File_Formats|Forensics image format]].
 +
This can be a time consuming process especially for disks with a large capacity.
  
==Windows Mobile 2003 Second Edition==
+
The process of disk imaging is also referred to as disk duplication.
This version of Windows Mobile 2003 was an upgrade on the first version and offered many improvements.  This version is powered by Windows CE 4.21, and adds support for 640x480 VGA resolution, portrait and landscape display modes, DPI settings, and many other improvements.
+
  
==Windows Mobile 5.0==
+
== Disk Imaging Solutions ==
Microsoft Windows Mobile 5.0, based off of Windows CE 5.0, was released on May 10, 2005. Microsoft Windows Mobile 5.0 brought many changes to the Pocket PC landscape. For one, with this release, the phone and PDA versions of the OS have merged into one encompassing OS, instead of two separate versions of the same one. Additionally, while past versions of Pocket PC software utilized the RAM of a PDA for program and data storage, Microsoft Windows Mobile 5.0 uses a PDA's hardware more like a traditional computer. The operating system and user data is stored in the more persistent ROM of the device, and RAM is used in a way more similar to that of a desktop PC. This has implications for forensics, as data stored on these devices is now less volatile.
+
See: [[:Category:Disk Imaging|Disk Imaging Solutions]]
  
=External Links=
+
== Common practice ==
[http://en.wikipedia.org/wiki/Windows_Mobile http://en.wikipedia.org/wiki/Windows_Mobile]
+
It common practice to use a [[Write Blockers|Write Blocker]] when imaging a pyhical disk. The write blocker is an additional measure to prevent write access to the disk.
 +
 
 +
Also see: [[DCO and HPA|Device Configuration Overlay (DCO) and Host Protected Area (HPA)]]
 +
 
 +
== Integrity ==
 +
Often when creating a disk image a [http://en.wikipedia.org/wiki/Cryptographic_hash_function cryptographic hash] is calculated of the entire disk. Commonly used cryptographic hashes are MD5, SHA1 and/or SHA256.
 +
 
 +
 
 +
By recalculating the integrity hash at a later time, one can determine if the data in the disk image has been changed. This by itself provides no protection against intentional tampering, but can indicate that the data was altered, e.g. due to corruption. The integrity hash does not indicate where int he data the alteration has occurred. Therefore some image tools and/or formats provide for additional integrity checks like:
 +
* A checksum
 +
* Parity data
 +
* [[Piecewise hashing]]
 +
 
 +
== Smart imaging ==
 +
Smart imaging is a combination of techniques to make the imaging process more intelligent.
 +
* Compressed storage
 +
* Deduplication
 +
* Selective imaging
 +
* Decryption while imaging
 +
 
 +
=== Compressed storage ===
 +
 
 +
A common technique to reduce the size of an image file is to compress the data. Where the compression method should be [http://en.wikipedia.org/wiki/Lossless_data_compression lossless].
 +
On modern computers, with multiple cores, the compression can be done in parallel reducing the output without prolonging the imaging process.
 +
Since the write speed of the target disk can be a bottleneck in imaging process, parallel compression can reduce the total time of the imaging process.
 +
[[Guymager]] was one of the first imaging tools to implement the concept of multi-process compression for the [[Encase image file format]]. This technique is now used by various imaging tools including [http://www.tableau.com/index.php?pageid=products&model=TSW-TIM Tableau Imager (TIM)]
 +
 
 +
Other techniques like storing the data sparse, using '''empty-block compression''' or '''pattern fill''', can reduce the total time of the imaging process and the resulting size of new non-encrypted (0-byte filled) disks.
 +
 
 +
=== Deduplication ===
 +
Deduplication is the process of determining and storing data that occurs more than once on-disk, only once in the image.
 +
It is even possible to store the data once for a corpus of images using techniques like hash based imaging.
 +
 
 +
=== Selective imaging ===
 +
Selective imaging is a technique to only make a copy of certain information on a disk like the $MFT on an [[NTFS]] volume with the necessary contextual information.
 +
 
 +
[[EnCase]] Logical Evidence Format (LEF) is an example of a selective image; although only file related contextual information is stored in the format by [[EnCase]].
 +
 
 +
=== Decryption while imaging ===
 +
Encrypted data is worst-case scenario for compression. Because the encryption process should be deterministic, a solution to reduce the size of an encrypted image is to store it non-encrypted and compressed and encrypt it again on-the-fly if required. Although this should be rare since the non-encrypted data is what undergoes analysis.
 +
 
 +
== Also see ==
 +
* [[:Category:Forensics_File_Formats|Forensics File Formats]]
 +
* [[Write Blockers]]
 +
* [[Piecewise hashing]]
 +
* [[Memory Imaging]]
 +
 
 +
== External Links ==
 +
* [http://www.tableau.com/pdf/en/Tableau_Forensic_Disk_Perf.pdf Benchmarking Hard Disk Duplication Performance in Forensic Applications], by [[Robert Botchek]]
 +
 
 +
=== Hash based imaging ===
 +
* [http://www.dfrws.org/2010/proceedings/2010-314.pdf Hash based disk imaging using AFF4], by [[Michael Cohen]], [[Bradley Schatz]]
 +
 
 +
[[Category:Disk Imaging]]

Revision as of 04:29, 28 July 2012

Information icon.png

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

Disk imaging is the process of making a bit-by-bit copy of a disk. Imaging (in more general terms) can apply to anything that can be considered as a bit-stream, e.g. a physical or logical volumes, network streams, etc.

The most straight-forward disk imaging method is reading a disk from start to end and writing the data to a Forensics image format. This can be a time consuming process especially for disks with a large capacity.

The process of disk imaging is also referred to as disk duplication.

Disk Imaging Solutions

See: Disk Imaging Solutions

Common practice

It common practice to use a Write Blocker when imaging a pyhical disk. The write blocker is an additional measure to prevent write access to the disk.

Also see: Device Configuration Overlay (DCO) and Host Protected Area (HPA)

Integrity

Often when creating a disk image a cryptographic hash is calculated of the entire disk. Commonly used cryptographic hashes are MD5, SHA1 and/or SHA256.


By recalculating the integrity hash at a later time, one can determine if the data in the disk image has been changed. This by itself provides no protection against intentional tampering, but can indicate that the data was altered, e.g. due to corruption. The integrity hash does not indicate where int he data the alteration has occurred. Therefore some image tools and/or formats provide for additional integrity checks like:

Smart imaging

Smart imaging is a combination of techniques to make the imaging process more intelligent.

  • Compressed storage
  • Deduplication
  • Selective imaging
  • Decryption while imaging

Compressed storage

A common technique to reduce the size of an image file is to compress the data. Where the compression method should be lossless. On modern computers, with multiple cores, the compression can be done in parallel reducing the output without prolonging the imaging process. Since the write speed of the target disk can be a bottleneck in imaging process, parallel compression can reduce the total time of the imaging process. Guymager was one of the first imaging tools to implement the concept of multi-process compression for the Encase image file format. This technique is now used by various imaging tools including Tableau Imager (TIM)

Other techniques like storing the data sparse, using empty-block compression or pattern fill, can reduce the total time of the imaging process and the resulting size of new non-encrypted (0-byte filled) disks.

Deduplication

Deduplication is the process of determining and storing data that occurs more than once on-disk, only once in the image. It is even possible to store the data once for a corpus of images using techniques like hash based imaging.

Selective imaging

Selective imaging is a technique to only make a copy of certain information on a disk like the $MFT on an NTFS volume with the necessary contextual information.

EnCase Logical Evidence Format (LEF) is an example of a selective image; although only file related contextual information is stored in the format by EnCase.

Decryption while imaging

Encrypted data is worst-case scenario for compression. Because the encryption process should be deterministic, a solution to reduce the size of an encrypted image is to store it non-encrypted and compressed and encrypt it again on-the-fly if required. Although this should be rare since the non-encrypted data is what undergoes analysis.

Also see

External Links

Hash based imaging