Difference between pages "Global Positioning System" and "Disk Imaging"

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The '''Global Positioning System''' ('''GPS''') is a satellite navigation system.
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{{expand}}
  
== Forensics ==
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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.
  
There are several places where GPS information can found. It can be very useful for forensic investigations in certain situations. GPS devices have expanded their capabilites and features as the technology has improved. Some of the most popular GPS devices today are made by [http://www.TomTom.com TomTom]. Some of the other GPS manufacturors include [http://www.garmin.com Garmin] and [http://www.magellangps.com Magellan].
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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]].
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This can be a time consuming process especially for disks with a large capacity.
  
[http://www.cortextech.com/tomtom910.jpg Picture of TomTom910]
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The process of disk imaging is also referred to as disk duplication.
  
TomTom provides a wide range of devices for biking, hiking, and car navigation. Depending on the capabilities of the model, several different types of digital evidence can be located on these devices. For instance, the [http://www.tomtom.com/products/product.php?ID=212&Category=0&Lid=1 TomTom 910] is basically a 20GB external harddrive. This model can be docked with a personal computer via a USB cable or through the use of Bluetooth technology. The listed features include the ability to store pictures, play MP3 music files, and connect to certain cell phones via bluetooth technology. Data commonly found on cell phones could easily be found on the TomTom910. Via the Bluetooth, the TomTom can transfer the entire contact list from your phone. The GPS unit also records your call logs and SMS messages. Research needs to be done to see if the TomTom stores actual trips conducted with the unit. This would include routes, times, and travel speeds.
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== Disk Imaging Solutions ==
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See: [[:Category:Disk Imaging|Disk Imaging Solutions]]
  
The TomTom unit connects to a computer via a USB base station. An examiner should be able to acquire the image of the harddrive through a USB write blocker. If not, it may be necessary to remove the hard drive from the unit.  
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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.
  
TomTom models such the TomTom One Regional, TomTom Europe, Go 510, Go 710 and the Go 720 store map data, favourites, and recent destinations on a removable SD card.  This allows the forensic examiner to remove the SD card and make a backup with a write blocked SD card reader.  The most important file for the forensic examiner will be the CFG file that is held in the map data directory.  This holds a list of all recent destinations that the user has entered into the device.  The information is held in a hex file and stores the represents grid coordinates of these locations. 
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Also see: [[DCO and HPA|Device Configuration Overlay (DCO) and Host Protected Area (HPA)]]
  
Certain TomTom models (Go 510, Go 910, Go 920 etc.) allow the user to pair their mobile phone to the device so they can use the TomTom as a hands free kit.  If the user has paired their phone to the TomTom device, then the TomTom will store the Bluetooth MAC ID for up to five phones, erasing the oldest if a sixth phone is paired.  Depending on the phone model paired with the TomTom, there may also be Call lists, contacts and text messages (sent & received) stored in the device too. Automated forensic analysis for TomTom GPS units is possible with software from Digivence - Forensic Analyser - TomTom Edition.  [http://www.digivence.com/SCREEN%20OPTIMISED%20REPORT%20-%20Demo%2011072007%20163219.htm Sample Report]
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== Integrity ==
 
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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.
=== Digital Camera Images with GPS Information ===
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Some recent digital cameras have built-in GPS receivers (or external modules you can connect to the camera). This makes it possible for the camera to record where extactly a photo was taken. This positioning information (latitude, longitude) can be stored in the [[Exif]] [[metadata]] header of [[JPEG]] files. Tools such as [[jhead]] can display the GPS information in the [[Exif]] headers.
 
  
=== Cell Phones with GPS ===
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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:
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* A checksum
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* Parity data
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* [[Piecewise hashing]]
  
Some recent cell phones (e.g. a [http://wiki.openezx.org Motorola EZX phone] such as the Motorola A780) have a built-in GPS receiver and navigation software. This software might record the paths travelled (and the date/time), which can be very useful in forensic investigations.
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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
  
== External Links ==
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=== Compressed storage ===
  
* [http://en.wikipedia.org/wiki/Global_Positioning_System Wikipedia: GPS]
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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].
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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, 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.
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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 again 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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* [[Piecewise hashing]]
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* [[Memory Imaging]]
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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]]
  
* [http://www.digivence.com Digivence: TomTom Forensic Analyser]
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[[Category:Disk Imaging]]

Revision as of 05:29, 28 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.

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