Difference between pages "Disk Imaging" and "Chip-Off Forensics"

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== Definition ==
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=== From Wikipedia ([http://en.wikipedia.org/wiki/Mobile_device_forensics#Forensic_desoldering http://en.wikipedia.org/wiki/Mobile_device_forensics#Forensic_desoldering]): ===
  
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.
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Commonly referred to as a "Chip-Off" technique within the industry - this is the last and most intrusive method to get a memory image is to desolder the non-volatile memory chip and connect it to a memory chip reader.  This method contains the potential danger of total data destruction: it is possible to destroy the chip and its content because of the heat and possible physical damage from desoldering.
  
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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=== Forensic Application ===
This can be a time consuming process especially for disks with a large capacity.
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The process of disk imaging is also referred to as disk duplication.
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Chip-Off forensics is an acquisition procedure which involves physically removing the NAND or flash IC from a device and reading it directly on an external NAND/Flash reader.  It is considered a last-option technique, as repairing the phone to a working state post-IC removal, is quite difficult.
  
== Disk Imaging Solutions ==
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== Tools and Equipment ==
See: [[:Category:Disk Imaging|Disk Imaging Solutions]]
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== Common practice ==
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* [[JTAG and Chip-Off Tools and Equipment]]
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.
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Also see: [[DCO and HPA|Device Configuration Overlay (DCO) and Host Protected Area (HPA)]]
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== Procedures ==
  
== Integrity ==
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* [[Chip-Off BlackBerry Curve 9300]]
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.
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* [[Chip-Off BlackBerry Curve 9320]]
 
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* [[Chip-Off BlackBerry Bold 9780]]
 
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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]]
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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. 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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* [[Imager NG Ideas]]
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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]]
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Revision as of 12:23, 30 October 2013

Definition

From Wikipedia (http://en.wikipedia.org/wiki/Mobile_device_forensics#Forensic_desoldering):

Commonly referred to as a "Chip-Off" technique within the industry - this is the last and most intrusive method to get a memory image is to desolder the non-volatile memory chip and connect it to a memory chip reader. This method contains the potential danger of total data destruction: it is possible to destroy the chip and its content because of the heat and possible physical damage from desoldering.

Forensic Application

Chip-Off forensics is an acquisition procedure which involves physically removing the NAND or flash IC from a device and reading it directly on an external NAND/Flash reader. It is considered a last-option technique, as repairing the phone to a working state post-IC removal, is quite difficult.

Tools and Equipment

Procedures