Difference between pages "JTAG Forensics" and "Gzip"

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== Definition ==
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{{expand}}
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=== From Wikipedia ([http://en.wikipedia.org/wiki/Joint_Test_Action_Group http://en.wikipedia.org/wiki/Joint_Test_Action_Group ]): ===
+
  
−
Joint Test Action Group (JTAG) is the common name for what was later standardized as the IEEE 1149.1 Standard Test Access Port and Boundary-Scan Architecture. It was initially devised for testing printed circuit boards using boundary scan and is still widely used for this application. Today JTAG is also widely used for IC debug ports. In the embedded processor market, essentially all modern processors support JTAG when they have enough pins. Embedded systems development relies on debuggers talking to chips with JTAG to perform operations like single stepping and breakpointing. Digital electronics products such as cell phones or a wireless access point generally have no other debug or test interfaces.
+
== File format ==
 +
The gzip file (.gz) format consists of:
 +
* a file header
 +
* optional headers
 +
** extra fields
 +
** original file name
 +
** comment
 +
** header checksum
 +
* a body, containing a DEFLATE-compressed payload
 +
* a file footer
  
−
=== Forensic Application ===
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=== File header ===
 +
The file header is 10 bytes in size and contains:
 +
{| class="wikitable"
 +
! align="left"| Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 2
 +
| 0x1f 0x8b
 +
| Signature (or identification byte 1 and 2)
 +
|-
 +
| 2
 +
| 1
 +
|
 +
| Compression Method
 +
|-
 +
| 3
 +
| 1
 +
|
 +
| Flags
 +
|-
 +
| 4
 +
| 4
 +
|
 +
| Last modification time <br> Contains a POSIX timestamp.
 +
|-
 +
| 8
 +
| 1
 +
|
 +
| Extra flags
 +
|-
 +
| 9
 +
| 1
 +
|
 +
| Operating system <br> Value that indicates on which operating system the gzip file was created.
 +
|}
  
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JTAG forensics is an acquisition procedure which involves connecting to the Standard Test Access Port (TAPs) on a device and instructing the processor to transfer the raw data stored on connected memory chips. Jtagging supported phones can be an extremely effective technique to extract a full physical image from devices that cannot be acquired by other means.
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==== Compression method ====
  
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== Tools and Equipment ==
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{| class="wikitable"
 +
! align="left"| Value
 +
! Identifier
 +
! Description
 +
|-
 +
| 0 - 7
 +
|
 +
| Reserved
 +
|-
 +
| 8
 +
| "deflate"
 +
| zlib compressed data
 +
|}
  
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* [[JTAG and Chip-Off Tools and Equipment]]
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==== Flags ====
  
−
== Procedures ==
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{| class="wikitable"
 +
! align="left"| Value
 +
! Identifier
 +
! Description
 +
|-
 +
| 0x01
 +
| FTEXT
 +
| If set the uncompressed data needs to be treated as text instead of binary data. <br> This flag hints end-of-line conversion for cross-platform text files but does not enforce it.
 +
|-
 +
| 0x02
 +
| FHCRC
 +
| The file contains a header checksum (CRC-16)
 +
|-
 +
| 0x04
 +
| FEXTRA
 +
| The file contains extra fields
 +
|-
 +
| 0x08
 +
| FNAME
 +
| The file contains an original file name string
 +
|-
 +
| 0x10
 +
| FCOMMENT
 +
| The file contains comment
 +
|-
 +
| 0x20
 +
|
 +
| Reserved
 +
|-
 +
| 0x40
 +
|
 +
| Reserved
 +
|-
 +
| 0x80
 +
|
 +
| Reserved
 +
|}
  
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* [[JTAG HTC Wildfire S]]
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<b>Note:</b> The FHCRC bit was never set by versions of gzip up to 1.2.4, even though it was documented with a different meaning in gzip 1.2.4.
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* [[JTAG Huawei TracFone M865C]]
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* [[JTAG Huawei TracFone H866C]]
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==== Extra flags ====
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* [[JTAG Huawei U8655]]
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If compression method is 8 the following extra flags can be defined:
−
* [[JTAG LG L45C TracFone]]
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{| class="wikitable"
−
* [[JTAG LG P930 (Nitro HD)]]
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! align="left"| Value
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* [[JTAG Samsung Galaxy S4 (SGH-I337)]]
+
! Identifier
 +
! Description
 +
|-
 +
| 0x02
 +
|
 +
| compressor used maximum compression, slowest algorithm
 +
|-
 +
| 0x04
 +
|
 +
| compressor used fastest algorithm
 +
|}
 +
 
 +
==== Operating System ====
 +
{| class="wikitable"
 +
! align="left"| Value
 +
! Identifier
 +
! Description
 +
|-
 +
| 0
 +
|
 +
| FAT filesystem (MS-DOS, OS/2, NT/Win32)
 +
|-
 +
| 1
 +
|
 +
| Amiga
 +
|-
 +
| 2
 +
|
 +
| VMS (or OpenVMS)
 +
|-
 +
| 3
 +
|
 +
| Unix
 +
|-
 +
| 4
 +
|
 +
| VM/CMS
 +
|-
 +
| 5
 +
|
 +
| Atari TOS
 +
|-
 +
| 6
 +
|
 +
| HPFS filesystem (OS/2, NT)
 +
|-
 +
| 7
 +
|
 +
| Macintosh
 +
|-
 +
| 8
 +
|
 +
| Z-System
 +
|-
 +
| 9
 +
|
 +
| CP/M
 +
|-
 +
| 10
 +
|
 +
| TOPS-20
 +
|-
 +
| 11
 +
|
 +
| NTFS filesystem (NT)
 +
|-
 +
| 12
 +
|
 +
| QDOS
 +
|-
 +
| 13
 +
|
 +
| Acorn RISCOS
 +
|-
 +
| 255
 +
|
 +
| unknown
 +
|}
 +
 
 +
=== Optional headers ===
 +
==== Extra fields ====
 +
<b>TODO: add description</b>
 +
 
 +
The extra field are variable of size and contains:
 +
{| class="wikitable"
 +
! align="left"| Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 2
 +
|
 +
| Extra field data size <br> Value in bytes.
 +
|-
 +
| 2
 +
| ...
 +
|
 +
| Extra field data
 +
|}
 +
 
 +
==== Original file name ====
 +
This is the original name of the file being compressed, with any directory components removed, and, if the file being compressed is on a file system with case insensitive names, forced to lower case.
 +
 
 +
Contains an ISO 8859-1 (LATIN-1) string with end-of-string character.
 +
 
 +
==== Comment ====
 +
Contains an ISO 8859-1 (LATIN-1) string with end-of-string character. Line breaks should be denoted by a single line feed character.
 +
 
 +
==== Header checksum ====
 +
The header checksum contain a CRC-16 that consists of the two least significant bytes of the CRC-32 for all bytes of the gzip header up to and not including the CRC-16.
 +
 
 +
=== File footer ===
 +
The file footer is 8 bytes in size and contains:
 +
{| class="wikitable"
 +
! align="left"| Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 4
 +
|
 +
| Checksum (CRC-32)
 +
|-
 +
| 4
 +
| 4
 +
|
 +
| Uncompressed data size <br> Value in bytes.
 +
|}
 +
 
 +
== External Links ==
 +
 
 +
* [http://www.gzip.org/format.txt The gzip file format], by the [http://www.gzip.org/ gzip project]
 +
* [http://www.gzip.org/algorithm.txt The gzip compression algorithm], by the [http://www.gzip.org/ gzip project]
 +
* [http://tools.ietf.org/html/rfc1952 RFC1952: GZIP file format specification version 4.3], by [[IETF]]
 +
* [http://en.wikipedia.org/wiki/Gzip Wikipedia: gzip]
 +
 
 +
[[Category:File Formats]]

Revision as of 03:05, 28 November 2013

Information icon.png

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

File format

The gzip file (.gz) format consists of:

  • a file header
  • optional headers
    • extra fields
    • original file name
    • comment
    • header checksum
  • a body, containing a DEFLATE-compressed payload
  • a file footer

File header

The file header is 10 bytes in size and contains:

Offset Size Value Description
0 2 0x1f 0x8b Signature (or identification byte 1 and 2)
2 1 Compression Method
3 1 Flags
4 4 Last modification time
Contains a POSIX timestamp.
8 1 Extra flags
9 1 Operating system
Value that indicates on which operating system the gzip file was created.

Compression method

Value Identifier Description
0 - 7 Reserved
8 "deflate" zlib compressed data

Flags

Value Identifier Description
0x01 FTEXT If set the uncompressed data needs to be treated as text instead of binary data.
This flag hints end-of-line conversion for cross-platform text files but does not enforce it.
0x02 FHCRC The file contains a header checksum (CRC-16)
0x04 FEXTRA The file contains extra fields
0x08 FNAME The file contains an original file name string
0x10 FCOMMENT The file contains comment
0x20 Reserved
0x40 Reserved
0x80 Reserved

Note: The FHCRC bit was never set by versions of gzip up to 1.2.4, even though it was documented with a different meaning in gzip 1.2.4.

Extra flags

If compression method is 8 the following extra flags can be defined:

Value Identifier Description
0x02 compressor used maximum compression, slowest algorithm
0x04 compressor used fastest algorithm

Operating System

Value Identifier Description
0 FAT filesystem (MS-DOS, OS/2, NT/Win32)
1 Amiga
2 VMS (or OpenVMS)
3 Unix
4 VM/CMS
5 Atari TOS
6 HPFS filesystem (OS/2, NT)
7 Macintosh
8 Z-System
9 CP/M
10 TOPS-20
11 NTFS filesystem (NT)
12 QDOS
13 Acorn RISCOS
255 unknown

Optional headers

Extra fields

TODO: add description

The extra field are variable of size and contains:

Offset Size Value Description
0 2 Extra field data size
Value in bytes.
2 ... Extra field data

Original file name

This is the original name of the file being compressed, with any directory components removed, and, if the file being compressed is on a file system with case insensitive names, forced to lower case.

Contains an ISO 8859-1 (LATIN-1) string with end-of-string character.

Comment

Contains an ISO 8859-1 (LATIN-1) string with end-of-string character. Line breaks should be denoted by a single line feed character.

Header checksum

The header checksum contain a CRC-16 that consists of the two least significant bytes of the CRC-32 for all bytes of the gzip header up to and not including the CRC-16.

File footer

The file footer is 8 bytes in size and contains:

Offset Size Value Description
0 4 Checksum (CRC-32)
4 4 Uncompressed data size
Value in bytes.

External Links

Retrieved from "http://forensicswiki.org/index.php?title=JTAG_Forensics&oldid=13128"