Difference between pages "Memory analysis" and "Gzip"

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'''Memory Analysis''' is the science of using a [[Tools:Memory Imaging|memory image]] to determine information about running programs, the [[operating system]], and the overall state of a computer. Because the analysis is highly dependent on the operating system, we have broken it into subpages:
+
{{expand}}
  
* [[Windows Memory Analysis]]
+
== File format ==
* [[Linux Memory Analysis]]
+
The gzip file (.gz) format consists of:
* [[FreeBSD Memory Analysis]]
+
* a file header
 +
* optional headers
 +
** extra fields
 +
** original file name
 +
** comment
 +
** header checksum
 +
* a body, containing a DEFLATE-compressed payload
 +
* a file footer
  
== Encryption Keys ==
+
=== 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.
 +
|}
  
Various types of encryption keys can be extracted during memory analysis.
+
==== Compression method ====
You can use [[AESKeyFinder]] to extract 128-bit and 256-bit [[AES]] keys and [[RSAKeyFinder]] to extract all private and public [[RSA]] keys from a memory dump [http://citp.princeton.edu/memory/code/]. [http://jessekornblum.com/research/volatility-plugins/cryptoscan.py cryptoscan.py] (plugin for the Volatility memory analysis framework) scans a memory image for [[TrueCrypt]] passphrases.
+
  
== See Also ==
+
{| class="wikitable"
 +
! align="left"| Value
 +
! Identifier
 +
! Description
 +
|-
 +
| 0 - 7
 +
|
 +
| Reserved
 +
|-
 +
| 8
 +
| "deflate"
 +
| zlib compressed data
 +
|}
  
* [[Tools:Memory Imaging]]
+
==== Flags ====
  
== Weblinks ==
+
{| 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
 +
|}
  
* [http://www.blackhat.com/presentations/bh-federal-06/BH-Fed-06-Burdach/bh-fed-06-burdach-up.pdf Mariusz Burdach: Finding Digital Evidence In Physical Memory] (PDF)
+
<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.
* [https://www.usenix.org/events/usenix05/tech/freenix/full_papers/movall/movall.pdf Paul Movall, Ward Nelson, Shaun Wetzstein: Linux Physical Memory Analysis] (PDF)
+
 
* [http://citp.princeton.edu/memory/ Lest We Remember: Cold Boot Attacks on Encryption Keys] ([http://citp.princeton.edu.nyud.net/pub/coldboot.pdf PDF])
+
==== Extra flags ====
 +
If compression method is 8 the following extra flags can be defined:
 +
{| class="wikitable"
 +
! align="left"| Value
 +
! 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 02:05, 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