Difference between pages "Global Positioning System" and "HFS+"

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The '''Global Positioning System''' ('''GPS''') is a satellite navigation system.
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HFS+, or Hierarchical File System Plus, is the file system designed by Apple Computer[http://www.apple.com] to supersede HFS. First introduced with Mac OS 8.1, one of the biggest differences was the lower allocation block size of 4kb, which increased performance and lowered fragmentation (See:  Technical Note TN1121). It also implemented Unicode (rather than Mac proprietary formats) for naming files.
  
== Forensics ==
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There are structurally many differences between HFS and HFS+, which are listed below[http://developer.apple.com/technotes/tn/tn1150.html#HFSPlusBasics]:
 +
<br><br>
 +
<CENTER><TABLE Border=1 cellpadding=2 cellspacing=0 width=75%>
 +
            <TR>
 +
              <TD>
 +
                  <P><B>Feature</B></p>
  
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 capabilities 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 manufacturers include [http://www.garmin.com Garmin] and [http://www.magellangps.com Magellan].
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              </TD><TD>
 +
                  <P><B>HFS</B></p>
 +
              </TD><TD>
 +
                  <P><B>HFS Plus</B></p>
 +
              </TD><TD>
 +
                  <P><B>Benefit/Comment</B></p>
 +
              </TD></TR>
  
=== TomTom ===
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            <TR>
 +
              <TD>
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                  <P>User visible name</p>
 +
              </TD><TD>
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                  <P>Mac OS Standard</p>
 +
              </TD><TD>
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                  <P>Mac OS Extended</p>
  
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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              </TD><TD>
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                  <P></p>
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              </TD></TR>
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            <TR>
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              <TD>
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                  <P>Number of allocation blocks</p>
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              </TD><TD>
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                  <P>16 bits worth</p>
  
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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              </TD><TD>
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                  <P>32 bits worth</p>
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              </TD><TD>
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                  <P>Radical decrease in disk space used on large
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                  volumes, and a larger number of files per volume.</p>
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              </TD></TR>
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            <TR>
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              <TD>
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                  <P>Long file names</p>
  
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 grid coordinates of these locations. 
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              </TD><TD>
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                  <P>31 characters</p>
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              </TD><TD>
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                  <P>255 characters</p>
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              </TD><TD>
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                  <P>Obvious user benefit; also improves
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                  cross-platform compatibility</p>
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              </TD></TR>
  
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.
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            <TR>
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              <TD>
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                  <P>File name encoding</p>
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              </TD><TD>
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                  <P>MacRoman</p>
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              </TD><TD>
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                  <P>Unicode</p>
  
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].  Whilst not shown in the example report, call history, contacts, text messages, Bluetooth MAC ID, and unit info is also automatically processed if available.
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              </TD><TD>
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                  <P>Allows for international-friendly file names,
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                  including mixed script names</p>
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              </TD></TR>
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            <TR>
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              <TD>
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                  <P>File/folder attributes</p>
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              </TD><TD>
 +
                  <P>Support for fixed size attributes (FileInfo and
 +
                  ExtendedFileInfo)</p>
  
Another tool for forensically analysing TomToms is [http://www.forensicnavigation.com TomTology]. This will retrieve all journey details from both live and unallocated space. It will tell you which is the home, favourites and recent destinations and will also tell you the last journey that was plotted and where the TomTom last had a GPS fix. It will also extract phone numbers if the device has been paired with a phone and will find deleted phone numbers, useful for potentially tracing a previous owner.
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              </TD><TD>
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                  <P>Allows for future meta-data extensions</p>
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              </TD><TD>
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                  <P>Future systems may use metadata for a richer
 +
                  Finder experience</p>
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              </TD></TR>
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            <TR>
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              <TD>
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                  <P>OS startup support</p>
  
=== Garmin ===
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              </TD><TD>
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                  <P>System Folder ID</p>
 +
              </TD><TD>
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                  <P>Also supports a dedicated startup file</p>
 +
              </TD><TD>
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                  <P>May help non-Mac OS systems to boot from HFS
 +
                  Plus volumes</p>
 +
              </TD></TR>
  
Garmin units connect to a PC in the same way as TomTom, via a USB cable. The unit will mount as a Mass Storage Unit, similar to a USB Memory Stick. After drivers for the unit have loaded, it is possible to navigate the Garmin unit's file system. Many of the files inside can easily be opened in a text or Hex editor.
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            <TR>
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              <TD>
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                  <P>catalog node size</p>
 +
              </TD><TD>
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                  <P>512 bytes</p>
 +
              </TD><TD>
 +
                  <P>4 KB</p>
  
Raw trip data including waypoints, date & time stamps, latitude & longitude coordinates and elevations can be extracted from the Current.gpx file located in the \Garmin\GPX\ folder. It can be viewed by opening the file with a text editor such as [http://notepad-plus.sourceforge.net/ Notepad++]. All recent trips are stored in this file.
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              </TD><TD>
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                  <P>Maintains efficiency in the face of the other
 +
                  changes. (This larger catalog node size is due to
 +
                  the much longer file names [512 bytes as opposed to
 +
                  32 bytes], and larger catalog records (because of
 +
                  more/larger fields)).</p>
 +
              </TD></TR>
 +
            <TR>
 +
              <TD>
 +
                  <P>Maximum file size</p>
 +
              </TD><TD>
 +
                  <P>2<SUP>31</SUP> bytes</p>
  
Data can also be easily viewed via [http://earth.google.com/ Google Earth]'s import feature. If available, Google Earth will import waypoints, tracks and routes from the unit. A slider bar in the program will show saved routes by date and time. When a specific waypoint is selected, a window will open that shows Lat/Long Coordinates, Altitude, Speed, Heading and Date/Time (Zulu).  
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              </TD><TD>
 +
                  <P>2<SUP>63</SUP> bytes</p>
 +
              </TD><TD>
 +
                  <P>Obvious user benefit, especially for multimedia
 +
                  content creators.</p></td>
 +
                  </tr>
 +
</table></CENTER>
 +
<br>
 +
An HFS+ volume contains five special files:
 +
<ol>
 +
<li>
 +
Catalog file - Describes the folder and file hierarchy of the volume. It is organized as a "balanced tree" for fast and efficient searches
 +
</li>
 +
<li>Extents overflow file - Additional extents (contiguous allocation blocks allocated to forks) are stored in a b-tree in this file
 +
</li>
 +
<li>
 +
Allocation file - Specifies whether an allocation block is free (similar to $Bitmap in NTFS). This is stored in a bitmap, specifying a free allocation block with a "clear bit"
 +
</li>
 +
<li>Attributes file - Contains attribute information regarding files or folders
 +
</li>
 +
<li>
 +
Startup file - Allows computers to boot that do have built in support for HFS+ file systems
 +
</li>
 +
</ol>
 +
<br>
 +
HFS+ also implements journaling, which allows fast recovery in the case of a crash or power outage. According to Apple, "The purpose of the journal is to ensure that when a group of related changes are being made, that either all of those changes are actually made, or none of them are made."[http://developer.apple.com/technotes/tn/tn1150.html#Journal]
  
With this data, raw or when viewed in Google Earth, entire trips can easily be reproduced giving exact time and locations for the GPS unit. It is unknown how many trips the unit is capable of storing or will store by default, but the [https://buy.garmin.com/shop/shop.do?pID=37418#nuvi260w Garmin Nuvi 260W] test unit had 16 days of trip data stored to memory.
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Apple technical notes are available for the HFS+ file system from their [http://developer.apple.com/cgi-bin/search.pl?q=HFS+&num=10&site=default_collection website].
 
+
=== Magellan ===
+
 
+
Magellan GPS units also connect to a PC via a USB cable. The [http://www.magellangps.com/products/product.asp?segID=354&prodID=2053 Magellan Roadmate 1400] unit tested runs a version of Windows CE. The operating system did not appear to be tailored to the specific unit and had options included in the menus that were not available (e.g. backup and restore functionality via a SD memory card slot that did not exist). Upon connecting the unit to a PC, it will mount as a Mass Storage Unit when and if it is recognized. 
+
 
+
Files that may contain useful information when opened in a text editor:
+
* /App/Unit.xml
+
** This file contains information about the unit such as Model and Serial number.
+
* /App/Media.cfg
+
** This file is a short list of what types of files are stored in the file structure. (e.g. User data is stored in /USR)
+
* /Sys/USBTRANS/Unit_ID.dat
+
** This file is similar to Unit.xml. It contains more information such as Operating System Version and Firmware version.
+
* /USR/TGUSERA.dat
+
** This file may contain addresses, phone numbers and some user set points such as "Home". There is no recognizable structure to this data so finding useful data is difficult.
+
* /USR/CITYHIST.dat
+
** This file may contain cities entered into the unit by a user. Like TGUSERA.dat, there is little structure here. Unfortunately, only City and State may be listed here.
+
 
+
Magellan provides [http://www.magellangps.com/products/map.asp?PRODID=1903 VantagePoint] software to view map and waypoint data. In order to use this software, the Magellan unit must be powered on prior to connecting it to a PC. It is unknown how useful the VantagePoint software is in collecting data as the software would not recognize the Roadmate 1400 unit. VantagePoint also did not support the .dat or .cfg files stored on the unit. [http://earth.google.com/ Google Earth] also supports Magellan units via its import feature. Earth lists Explorist and Serial as available import options.
+
+
 
+
=== Digital Camera Images with GPS Information ===
+
 
+
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 exactly 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 ===
+
 
+
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.
+
  
 
== External Links ==
 
== External Links ==
 +
* [http://web.archive.org/web/20090530120010/http://developer.apple.com/technotes/tn/tn1121.html Internet Archive Copy of: Technical Note TN1121], originally found on http://developer.apple.com/technotes/tn/tn1121.html#HFSPlus
  
* [http://www.gpsforensics.org GPSForensics.org - A communitiy dedicated to GPS device forensics]
+
[[Category:Disk file systems]]
 
+
* [http://en.wikipedia.org/wiki/Global_Positioning_System Wikipedia: GPS]
+
 
+
* [http://www.digivence.com Digivence: TomTom Forensic Analyser]
+
 
+
* [http://www.paraben-forensics.com/catalog/product_info.php?cPath=25&products_id=405 Paraben's Device Seizure]
+
 
+
* [http://www.forensicnavigation.com TomTology by Forensic Navigation]
+
 
+
* [http://www.berlacorp.com/blackthorn.html Berla Corp.'s Blackthorn]
+

Revision as of 00:21, 21 July 2012

HFS+, or Hierarchical File System Plus, is the file system designed by Apple Computer[1] to supersede HFS. First introduced with Mac OS 8.1, one of the biggest differences was the lower allocation block size of 4kb, which increased performance and lowered fragmentation (See: Technical Note TN1121). It also implemented Unicode (rather than Mac proprietary formats) for naming files.

There are structurally many differences between HFS and HFS+, which are listed below[2]:

Feature

HFS

HFS Plus

Benefit/Comment

User visible name

Mac OS Standard

Mac OS Extended

Number of allocation blocks

16 bits worth

32 bits worth

Radical decrease in disk space used on large volumes, and a larger number of files per volume.

Long file names

31 characters

255 characters

Obvious user benefit; also improves cross-platform compatibility

File name encoding

MacRoman

Unicode

Allows for international-friendly file names, including mixed script names

File/folder attributes

Support for fixed size attributes (FileInfo and ExtendedFileInfo)

Allows for future meta-data extensions

Future systems may use metadata for a richer Finder experience

OS startup support

System Folder ID

Also supports a dedicated startup file

May help non-Mac OS systems to boot from HFS Plus volumes

catalog node size

512 bytes

4 KB

Maintains efficiency in the face of the other changes. (This larger catalog node size is due to the much longer file names [512 bytes as opposed to 32 bytes], and larger catalog records (because of more/larger fields)).

Maximum file size

231 bytes

263 bytes

Obvious user benefit, especially for multimedia content creators.


An HFS+ volume contains five special files:

  1. Catalog file - Describes the folder and file hierarchy of the volume. It is organized as a "balanced tree" for fast and efficient searches
  2. Extents overflow file - Additional extents (contiguous allocation blocks allocated to forks) are stored in a b-tree in this file
  3. Allocation file - Specifies whether an allocation block is free (similar to $Bitmap in NTFS). This is stored in a bitmap, specifying a free allocation block with a "clear bit"
  4. Attributes file - Contains attribute information regarding files or folders
  5. Startup file - Allows computers to boot that do have built in support for HFS+ file systems


HFS+ also implements journaling, which allows fast recovery in the case of a crash or power outage. According to Apple, "The purpose of the journal is to ensure that when a group of related changes are being made, that either all of those changes are actually made, or none of them are made."[3]

Apple technical notes are available for the HFS+ file system from their website.

External Links