Difference between pages "Residual Data" and "Disk Imaging"

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Residual Data is data that is unintentionally left behind on computer media. In forensic usage, remnant data is typically left behind after attempts have been made to delete the data, after the data has been forgotten, or after the media on which the data resides has been decomissioned.
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{{expand}}
  
Residual data appears at all levels of modern computer systems:
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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.
* Computer systems that are discarded.
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* Partitions in hard drives that are deleted.
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* Files on hard drives that are deleted but not overwritten.
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* Snippets of text in Microsoft Word files.
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* Heap variables that are freed with '''free()'''
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* Automatic variables left on the stack of languages like C or garbage collected in languages like Java.
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=Papers=
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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]].
Byers, Simon. [[Media:Scalable Exploitation.pdf|Scalable Exploitation of, and Responses to Information Leakage Through Hidden Data in Published Documents]], AT&T Research, April 2003
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This can be a time consuming process especially for disks with a large capacity.
  
Chow, J., B. Pfaff, T. Garfinkel, K. Christopher, M. Rosenblum, 
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== Disk Imaging Solutions ==
[[Media:Tainbochs.pdf|Understanding Data Lifetime via Whole System Simulation]], Proceedings of the 13th USENIX Security Symposium, 2004.
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See: [[:Category:Disk Imaging|Disk Imaging Solutions]]
  
Garfinkel, S. and Shelat, A., "Remembrance of Data Passed: A Study of Disk Sanitization Practices," IEEE Security and Privacy, January/February 2003.
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== Common practice ==
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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.
  
=See Also=
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Also see: [[DCO and HPA|Device Configuration Overlay (DCO) and Host Protected Area (HPA)]]
* [[Sanitizing Tools]]
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* [[Remnant Data]]
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== Error tolerance and recovery ==
* [http://www.iphoneatlas.com/2008/05/19/refurbished-iphones-may-contain-other-users-personal-data/ Remnant data on iPhones]
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...
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== Smart imaging ==
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Smart imaging is a combination of techniques to make the imaging process more intelligent.
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* Compressed storage
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* Deduplication
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* Selective imaging
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* Decryption while imaging
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=== Compressed storage ===
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A common technique to reduce the size of an image file is to compress the data.
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On modern computers, with multiple cores, the compression can be done in parallel reducing the output without prolonging the imaging process.
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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.
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[[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)]
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Other techniques like storing the data sparse or '''empty-block compression''' can reduce the total time of the imaging process and the resulting size of new non-encrypted (0-byte filled) disks.
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=== Deduplication ===
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Deduplication is the process of determining and storing data that occurs more than once on-disk, only once in the image.
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It is even possible to store the data once for a corpus of images using techniques like hash based imaging.
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=== Selective imaging ===
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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.
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[[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]].
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=== Decryption while imaging ===
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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 on-the-fly if required. Although this should be rare since the non-encrypted data is what undergoes analysis.
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== Also see ==
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* [[:Category:Forensics_File_Formats|Forensics File Formats]]
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* [[Write Blockers]]
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== External Links ==
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* [http://www.tableau.com/pdf/en/Tableau_Forensic_Disk_Perf.pdf Benchmarking Hard Disk Duplication Performance in Forensic Applications], by [[Robert Botchek]]
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=== Hash based imaging ===
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* [http://www.dfrws.org/2010/proceedings/2010-314.pdf Hash based disk imaging using AFF4], by [[Michael Cohen]], [[Bradley Schatz]]
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[[Category:Disk Imaging]]

Revision as of 05:55, 27 July 2012

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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.

Contents

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)

Error tolerance and recovery

...

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. 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 or empty-block compression 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 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