Expert Witness Compression Format (EWF)

EWF is short for Expert Witness Compression Format. It is a file type used to store storage media images for digital forensic purposes. It is currently widely used in the field of computer forensics in proprietary tooling like EnCase en FTK. The original specification of the format was provided by ASR Data for the SMART application.

The EWF format was succeeded by the Expert Witness Compression Format version 2 in EnCase 7 (EWF2-Ex01 and EWF2-Lx01). EnCase 7 also uses a different version of EWF-L01 then its predecessors.

Overview

The Expert Witness Compression Format (EWF) is used to store:

• storage media images, such as hard disks, USB sticks, optical disks
• individual volumes or partitions
• “physical” RAM and process memory

EWF can store data compressed or uncompressed, in a single image in one or more segment files. Each segment file consist of a standard header, followed by multiple sections. A single section cannot span multiple files. Sections are arranged back-to-back.

Terminology

In this document when referred to the EWF format it refers to the original specification by ASR Data. The newer formats like that of EnCase are deducted from the original specification and will be referred to as the EWF-E01, because of the default file extension. Whereas the Logical File Evidence (LVF) format introduced in EnCase 5, which is also stored in the EWF format will be referred to as EWF-L01. The SMART format is viewed separately to allow for discussion if the implementation differs from the specification by ASR Data and will be referred to as the EWF-S01, because of the default file extension.

All offsets are relative to the beginning of an individual section, unless otherwise noted. EnCase allows a maximum size of a segment file to be 2000 MiB. This has to do with the size of the offset of the chunk of media data. This is a 32 bit value where the most significant bit (MSB) is used as a compression flag. Therefore the maximum offset size (31 bit) can address about 2048 MiB. In EnCase 6.7 an addition was made to the table value to provide for a base offset to allow for segment files greater than 2048 MiB.

A chunk is defined as the sector size (per default 512 bytes) multiplied by the block size, the number of sectors per chunk (block) (per default 64 sectors). The data within the EWF format is stored in little-endian. The terms block and chunk are used intermittently.

Segment file

EWF stores data in one or more segment files (or segments). Each segment file consists of:

• A file header.
• One or more sections.

File header

Each segment file starts with a file header.

EWF defines that the file header consists of 2 parts, namely:

• a signature part
• fields part

EWF, EWF-E01 and SMART (EWF-S01)

The file header, used by both the EWF-E01 and SMART (EWF-S01) formats, is 13 bytes in size and consists of:

The segment number contains a number which refers to the number of the segment file, starting with 1 for the first file.

Note this means there could only be a maximum of 65535 (0xffff) files, if it is an unsigned value.

EWF-L01

The file header, used by the EWF-L01 format, is 13 bytes in size and consists of:

The segment number contains a number which refers to the number of the segment file, starting with 1 for the first file.

Note this means there could only be a maximum of 65535 (0xffff) files, if it is an unsigned value.

Segment file extensions

The SMART (EWF-S01) and the EWF-E01 formats use a different naming convention for the segment files.

SMART (EWF-S01)

The SMART (EWF-S01) extension naming has two distinct parts.

• The first segment file has the extension ‘.s01’.
  • The next segment file has the extension ’.s02.
  • This will continue up to ‘.s99’.
• After which the next segment file has the extension ‘.saa’.
  • The next segment file has the extension ‘.sab’.
  • This will continue up to ‘.saz’.
  • The next segment file has the extension ‘.sba’.
  • This will continue up to ‘.szz’.
  • The next segment file has the extension ‘.faa’.
  • This will continue up to ‘.zzz’.
  • Not confirmed but other sources report it will even continue to the use the extensions ‘.{aa’.

Keramics supports extensions up to .zzz

EWF-E01

The EWF-E01 extension naming has two distinct parts.

• The first segment file has the extension ‘.E01’.
  • The next segment file has the extension ’.E02.
  • This will continue up to ‘.E99’.
• After which the next segment file has the extension ‘.EAA’.
  • The next segment file has the extension ‘.EAB’.
  • This will continue up to ‘.EAZ’.
  • The next segment file has the extension ‘.EBA’.
  • This will continue up to ‘.EZZ’.
  • The next segment file has the extension ‘.FAA’.
  • This will continue up to ‘.ZZZ’.
  • Not confirmed but other sources report it will even continue to the use the extensions ‘.[AA’.

Keramics supports extensions up to .ZZZ

EWF-L01

The EWF-L01 extension naming has two distinct parts.

• The first segment file has the extension ‘.L01’.
  • The next segment file has the extension ’.L02.
  • This will continue up to ‘.L99’.
• After which the next segment file has the extension ‘.LAA’.
  • The next segment file has the extension ‘.LAB’.
  • This will continue up to ‘.LAZ’.
  • The next segment file has the extension ‘.LBA’.
  • This will continue up to ‘.LZZ’.
  • The next segment file has the extension ‘.MAA’.
  • This will continue up to ‘.ZZZ’.
  • Not confirmed but other sources report it will even continue to the use the extensions ‘.[AA’.

Keramics supports extensions up to .ZZZ

Segment file set identifier GUID

Segment file sets do not have a strict unique identifier. However the volume section contains a GUID that can be used for this purpose. Where:

• linen 5 to 6 use a time and MAC address based version (1) of the GUID
• EnCase 5 to 7 and linen 6 to 7 use a random based version (4) of the GUID

Note that in linen 6 the switch from a version 1 to 4 GUID was somewhere made between version 6.01 and 6.19.

See RFC4122 for more information about the different GUID versions.

The sections

The remainder of the segment file consists of sections. Every section starts with the same data this will be referred to as the section header.

Section header

The section header consist of 76 bytes, it contains information about a specific section.

Some sections contain additional data, refer to paragraph section types for more information.

Note Expert Witness 1.35 (for Windows) does not set the section size.

Note that in EnCase 2 DOS version the padding itself does not contains 0-byte values but data, probably the memory is not filled with 0-byte values.

Section types

There are multiple section types. ASR Data - E01 Compression Format defines the following:

• Header section
• Volume section
• Table section
• Next and Done section

The following sections type were found analyzing more recent EnCase files (EWF-E01):

• Header2 section
• Disk section
• Sectors section
• Table2 section
• Data section
• Error2 section
• Session section
• Hash section
• Digest section

The following sections type were found analyzing more recent EnCase files (EWF-L01):

• Ltree section
• Ltypes section

Header2 section

The header2 section is identified in the section data type field as “header2”. Some aspects of this section are:

• Found in EWF-E01 in EnCase 4 to 7, and EWF-L01 in EnCase 5 to 7
• Found at the start of the first segment file. Not found in subsequent segment files.
• The same header2 section is found twice directly after one and other.

The additional data this section contains is the following:

The information about the acquired media consists of zlib compressed data. It contains text in UTF16 format specifying information about the acquired media. The text multiple lines separated by an end of line character(s).

The first 2 bytes of the UTF16 string are the byte order mark (BOM):

• 0xff 0xfe for UTF-16 litte-endian
• 0xfe 0xff for UTF-16 big-endian

In the next paragraphs the various variants of the header2 section are described.

EnCase 4 (EWF-E01)

In EnCase 4 (EWF-E01) the header2 information consist of 5 lines, and contains the equivalent information as the header section.

The end of line character(s) is a newline (0x0a).

Note this end of line character differs from the one used in the header section.

The 3rd and the 4th line consist of the following tab (0x09) separated values.

Also see header2 values

Note the hashing algorithm is the same as for the header section.

EnCase 5 to 7 (EWF-E01)

In EnCase 5 to 7 (EWF-E01) the header2 information consist of 17 lines, and contains:

The end of line character(s) is a newline (0x0a).

Main category

The 3rd and the 4th line consist of the following tab (0x09) separated values.

Note the actual values in this category are dependent on the version of EnCase.

Also see header2 values

Note that both the acquiry and system date and time are empty in a file created by winen.

Note that the date values in the header section (not the header2 section) are set to: “Thu Jan 1 00:00:00 1970”. Where the time is dependent on the time zone and daylight savings.

Note that in a Logicube Dossier generated header2 section an additional emtpy value in the 4th line was observed. The number of values in the 3rd and 4th can differ.

Sources category

Line 6 the srce category contains information about acquisition sources.

TODO: describe what a source is in the context of EnCase.

Line 7 consists of 2 values, namely the values are “0 1”.

The 8th line consist of the following tab (0x09) separated values.

Note that the actual values in this category are dependent on the version of EnCase.

Line 9 consists of 2 values, namely the values are “0 0”.

Line 10 contains the values defined by line 8.

Note the default values of some of these values has changed around EnCase 6.12.

If the “ha” value contains “00000000000000000000000000000000” this means the MD5 hash is not set. The same applies for the “sha” value when it contains “0000000000000000000000000000000000000000” the SHA1 has is not set.

Subjects category

Line 12 the sub category contains information about subjects.

TODO: describe what a subject is in the context of EnCase.

Line 13 consists of 2 values, namely the values are “0 1”.

The 14th line consist of the following tab (0x09) separated values.

Line 15 consists of 2 values, namely the values are “0 0”.

Line 16 contains the values defined by line 14.

Note that the default values of some of these values has changed around EnCase 6.12.

EnCase 5 to 7 (EWF-L01)

The EnCase 5 to 7 (EWF-E01) header2 section specification also applies to the EnCase 5 to 7 (EWF-L01) format. However:

• both the acquired and system date and time are not set

Header2 values

Note the restrictions were tested with EnCase 7.02.01, older versions could have a restriction of 40 characters instead of 3000 characters.

Extents header value

An extents header value consist of:

number of entries
entries that consist of: S <1> <2> <3>

Header section

The header section is identified in the section data type field as “header”. Some aspects of this section are:

• Defined in ASR Data - E01 Compression Format
• Found in EWF-E01 in EnCase 1 to 7 or linen 5 to 7 or FTK Imager, EWF-L01 in EnCase 5 to 7, and SMART (EWF-S01)
• Found at the start of the first segment file or in EnCase 4 to 7 after the header2 section in the first segment file. Typically not found in subsequent segment files with the exception of Logicube Dossier generated EWF-E01 files.

The additional data this section contains is the following:

The information about the acquired media consists of zlib compressed data. It contains text in ASCII format specifying information about the acquired media. The text multiple lines separated by an end of line character(s).

In the next paragraphs the various variants of the header section are described. In all cases the information consists of at least 4 lines:

An additional 5th line is found in FTK Imager, EnCase 1 to 7 (EWF-E01).

EWF format

Some aspects of this section are:

• ASR Data - E01 Compression Format specifies the end of line character(s) is a newline (0x0a).

According to ASR Data - E01 Compression Format the 3rd and the 4th line consist of the following tab (0x09) separated values:

Also see header values

ASR Data - E01 Compression Format states that the Expert Witness Compression uses ‘f’, fastest compression.

EnCase 1 (EWF-E01)

Some aspects of this section are:

• The header section is defined only once.
• It is the first section of the first segment file. It is not found in subsequent segment files.
• The header data itself is compressed using zlib.
• The end of line character(s) is a carriage return (0x0d) followed by a newline (0x0a).

The 3rd and the 4th line consist of the following tab (0x09) separated values“

Also see header values

SMART (EWF-S01)

Some aspects of this section are:

• The header section is defined once.
• It is the first section of the first segment file. It is not found in subsequent segment files.
• The header data is always processed by zlib, however the same compression level is used as for the chunks. This could mean compression level 0 which is no compression.

The SMART format uses the FTK Imager (EWF-E01) specification for this section. Note that this could be something FTK Imager specific.

EnCase 2 and 3 (EWF-E01)

Some aspects of this section are:

• The same header section defined twice.
• It is the first and second section of the first segment file. It is not found in subsequent segment files.
• The header data itself is compressed using zlib.
• The end of line character(s) is a carriage return (0x0d) followed by a newline (0x0a).

The 3rd and the 4th line consist of the following tab (0x09) separated values:

Also see header values

EnCase 4 to 7 (EWF-E01)

Some aspects of this section are:

• The header is defined only once.
• It resides after the header2 sections of the first segment file. It is not found in subsequent segment files.
• The header data itself is compressed using zlib.
• The end of line character(s) is a carriage return (0x0d) followed by a newline (0x0a).

The 3rd and the 4th line consist of the following tab (0x09) separated values:

Also see header values

linen 5 to 7 (EWF-E01)

Some aspects of this section are:

• The same header section defined twice.
• It is the first and second section of the first segment file. It is not found in subsequent segment files.
• The header data itself is compressed using zlib.
• The end of line character(s) is a newline (0x0a).

The header information consist of 18 lines

The remainder of the string contains the following information:

The end of line character(s) is a newline (0x0a).

Main category - linen 5

The 3rd and the 4th line consist of the following tab (0x09) separated values.

Note the actual values in this category are dependent on the version of linen.

Also see header values

Main category - linen 6 to 7

The 3rd and the 4th line consist of the following tab (0x09) separated values.

Note the actual values in this category are dependent on the version of linen.

Note as of linen 6.19 the acquire date and time is in UTC and the system date and time is in local time. Where as before both values were in local time.

Also see header values

Sources category

Line 6 the srce category contains information about acquisition sources

TODO: describe what a source is in the context of EnCase.

Line 7 consists of 2 values, namely the values are “0 1”.

The 8th line consist of the following tab (0x09) separated values.

Line 9 consists of 2 values, namely the values are “0 0”.

Line 10 contains the values defined by line 8.

Note the default values of some of these values has changed around linen 6.19 or earlier.

Subjects category

Line 12 the sub category contains information about subjects.

TODO: describe what a subject is in the context of EnCase.

Line 13 consists of 2 values, namely the values are “0 1”.

The 14th line consist of the following tab (0x09) separated values.

Line 15 consists of 2 values, namely the values are “0 0”.

Line 16 contains the values defined by line 14.

Note the default values of some of these values has changed around linen 6.19 or earlier.

FTK Imager (EWF-E01)

Some aspects of this section are:

• In FTK Imager (EWF-E01) the same header section defined twice.
• It is the first and second section of the first segment file. It is not found in subsequent segment files.
• The header data itself is compressed using zlib. Note that the compression level can be none and therefore the header looks uncompressed.
• In FTK Imager the end of line character(s) is a newline (0x0a).

The 3rd and the 4th line consist of the following tab (0x09) separated values:

Also see header values

EnCase 5 to 7 (EWF-L01)

The EnCase 4 to 7 (EWF-E01) header section specification is also used for the EnCase 5 to 7 (EWF-L01) format, with the following aspects:

• In EnCase 5 both the acquired and system date and time are set to 0.
• In EnCase 6 and 7 both the acquired and system date and time are set to Jan 1, 1970 00:00:00 (the time is dependent on the local timezone and daylight savings)

Header values

Note the restrictions were tested with EnCase 7.02.01, older versions could have a restriction of 40 characters instead of 3000 characters.

Date and time header value

In EnCase a date and time contains a string of individual values separated by a space, e.g. “2002 3 4 10 19 59”, which represents March 4, 2002 10:19:59.

In linen a date and time contains a string with a POSIX 32-bit epoch timestamp, e.g. “1142163845” which represents the date: March 12 2006, 11:44:05

Extents header value

An extents header value consist of:

number of entries
entries that consist of: S <1> <2> <3>

Compression header value

A compression header value consist of a single character that represent the compression level.

Notes

There should not be a tab, carriage return and newline characters within the text in the 4th line. Or is there a method to escape these characters?

ASR Data - E01 Compression Format states that these characters should not be used in the free form text. Need to confirm this, the specification only speaks of a newline character.

Currently the password has no a additional value than allow an application check it. The data itself is not protected using the password. The password hashing algorithm is unknown. Need to find out. And does the algorithm differ per EnCase version? probably not. The algorithm does not differ in EnCase 1 to 7. FTK Imager does not bother with a password.

Volume section

The volume section is identified in the section data type field as “volume”. Some aspects of this section are:

• Defined in ASR Data - E01 Compression Format
• Found in EWF-E01 in EnCase 1 to 7 or linen 5 to 7 or FTK Imager, EWF-L01 in EnCase 5 to 7, and SMART (EWF-S01)
• Found after the header section of the first segment file. Not found in subsequent segment files.

In the next paragraphs the various versions of the volume section are described.

EWF specification

The specification according to ASR Data - E01 Compression Format.

The volume section data is 94 bytes in size and consists of:

The number of chunks is a 32-bit value this means it maximum of addressable chunks would be: 4294967295 (= 2^32 - 1). For a chunk size of 32768 x 4294967295 = about 127 TiB. The maximum segment file amount is 2^16 - 1 = 65535. This allows for an equal number of storage if a segment file is filled to its maximum number of chunks.

However Keramics is restricted at 14295 segment files, due to the extension naming schema of the segment files.

SMART (EWF-S01)

The SMART format uses the EWF specification for this section.

In SMART the signature (reverse) value is the string “SMART” (0x53 0x4d 0x41 0x52 0x54) instead of the file header signature.

FTK Imager, EnCase 1 to 7 and linen 5 to 7 (EWF-E01)

The specification for FTK Imager, EnCase 1 to 7 and linen 5 to 7.

The volume section data is 1052 bytes in size and consists of:

TODO: a value that could be in the volume is the RAID stripe size

Note that EnCase requires for media that contains no partition table that the is physical media flag is not set and vice versa. Other tools like FTK check the actual storage media data.

EnCase 5 to 7 (EWF-L01)

The EWF-L01 format uses the EnCase 5 (EWF-E01) volume section specification. However:

• the volume type contains 0x0e
• the number of chunks is 0
• the number of bytes per sectors is some kind of block size value (4096), perhaps the source file system block size
• the sectors count, represents some other value because (sector_size x sector_amount != total_size). The total size is in the ltree section.

Media type

Note that FTK imager versions, before version 2.9, set the storage media to fixed (0x01). The exact version of FTK imager where this behavior changed is unknown.

Media flags

Note that if both the the Fastbloc and Tableau write blocker media flags are set EnCase only shows the Fastbloc.

Compression level

Note that EnCase 7 no longer provides the fast and best compression options.

Disk section

The disk section is identified in the section data type field as “disk”. Some aspects of this section are:

• Not defined in ASR Data - E01 Compression Format.
• Not found in SMART (EWF-S01).

With a disk section in an FTK Imager 2.3 (EWF-E01) image it was confirmed that the disk section is the same as the volume section.

Note that the disk section was found only in FTK Imager 2.3 when acquiring a physical disk not a floppy. This requires additional research, it is currently assumed that the disk section some old method to differentiate between a partition (volume) image or a physical disk image.

Data section

The data section is identified in the section data type field as “data”. Some aspects of this section are:

• Not defined in ASR Data - E01 Compression Format.
• Found in EWF-E01 in EnCase 1 to 7 or linen 5 to 7 or FTK Imager, and EWF-L01 in EnCase 5 to 7. Not found in SMART (EWF-S01).
• For multiple segment files it does not reside in the first segment file. For a single segment file it does.
• Found after the last table2 section in a single segment file or for multiple segment files at the start of the segment files, except for the first.
• The data section has data it should should contain the same information as the volume section.

The data section is a copy of the volume section.

FTK Imager, EnCase 1 to 7 and linen 5 to 7 (EWF-E01)

Note that in Logicube products (Talon (firmware predating April 2013) and Forensic dossier (before version 3.3.3RC16)) the checksum is not calculated and set to 0.

Sectors section

The sectors section is identified in the section data type field as “sectors”. Some aspects of this section are:

• Not defined in ASR Data - E01 Compression Format.
• Found in EWF-E01 in EnCase 2 to 7, or linen 5 to 7 or FTK Imager, EWF-L01 in EnCase 5 to 7. Not found in EnCase 1 (EWF-E01) or SMART (EWF-S01).
• The first sectors section can be found after the volume section in the first segment file or at the after the data section in subsequent segment files. Successive sector data sections are found after the sector table2 section.

The sectors section contains the actual chunks of media data.

• The sectors section can contain multiple chunks.
• The default size of a chunk is 32768 bytes of data (64 standard sectors, with a size of 512 bytes per sector). It is possible in EnCase 5 and 6 and linen 5 and 6 to change the number of sectors per block to 64, 128, 256, 1024, 2048, 4096, 8192, 16384 or 32768. In EnCase 7 and linen 7 this has been reduced to 64, 128, 256, 1024.

Data chunk

The first chunk is often located directly after the section header, although the format does not require this.

When the data is compressed and the compressed data (with checksum) is larger than the uncompressed data (without the checksum) the data chunk is stored uncompressed. The default size of a chunk is 32768 bytes of data (64 standard sectors).

An uncompressed data chunk is of variable size and consists of:

The compressed data chunk consist of zlib compressed data. The checksum of the compressed data chunk is part the zlib compressed data format.

Optical disc images

For a MODE-1 CD-ROM optical disc image EnCase only seems to support 2048 bytes per sector (the data).

The raw sector size of a MODE-1 CD-ROM is 2352 bytes in size and consists of:

TODO: add information about Mode-2 and Mode-XA

Table section

The table section is identified in the section data type field as “table”. Some aspects of this section are:

• Defined in ASR Data - E01 Compression Format.
• Found in EWF-E01 in EnCase 1 to 7 or linen 5 to 7 or FTK Imager, EWF-L01 in EnCase 5 to 7, and SMART (EWF-S01)

Note that the offsets within the section header are 8 bytes (64 bits) of size while the offsets in the table entry array are 4 bytes (32 bits) in size.

In the next paragraphs the various versions of the table section are described.

EWF specification

Some aspects of the table section according to the EWF specification are:

• The first table section resides after the volume section in the first segment file or after the file header in subsequent segment files.
• It can be found in every segment file.

The table section consists of:

• the table header
• an array of table entries
• the data chunks

Table header

The table header is 24 bytes in size and consists of:

According to ASR Data - E01 Compression Format

• the number of entries, contains 0x01
• the table can hold 16375 entries if more entries are required an additional table section should be created.

Table entry

The table entry is 4 bytes in size and consists of:

The most significant bit (MSB) in the chunk data offset indicates if the chunk is compressed (1) or uncompressed (0).

A chunk data offset points to the start of the chunk of media data, which resides in the same table section within the segment file. The offset contains a value relative to the start of the file.

Data chunk

The first chunk is often located directly after the last table entry, although the format does not require this.

A data chunk is always compressed even when no compression is required. This approach provides a checksum for each chunk. The default size of a chunk is 32768 bytes of data (64 standard sectors). The resulting size of the “compressed” chunk can therefore be larger than the default chunk size.

Note that this was deducted from the behavior of FTK Imager for SMART (EWF-S01).

The compressed data chunk consist of zlib compressed data. The checksum of the compressed data chunk is part the zlib compressed data format.

SMART (EWF-S01)

The table section in the SMART (EWF-S01) format is equivalent to that of the EWF specification.

EnCase 1 (EWF-E01)

Some aspects of this section are:

• The table section resides after the volume section in the first segment file or after the file header in subsequent segment files.
• It can be found in every segment file.

The table section consists of:

• the table header
• an array of table entries
• the table footer
• the data chunks

Table header

The table header is 24 bytes in size and consists of:

The table can hold 16375 entries if more entries are required an additional table section should be created.

Table entry

The table entry is 4 bytes in size and consists of:

The most significant bit (MSB) in the chunk data offset indicates if the chunk is compressed (1) or uncompressed (0).

A chunk data offset points to the start of the chunk of media data, which resides in the same table section within the segment file. The offset contains a value relative to the start of the file.

Table footer

The table footer is 4 bytes in size and consists of:

Data chunk

The first chunk is often located directly after the table footer, although the format does not require this.

When the data is compressed and the compressed data (with checksum) is larger than the uncompressed data (without the checksum) the data chunk is stored uncompressed. The default size of a chunk is 32768 bytes of data (64 standard sectors).

An uncompressed data chunk is of variable size and consists of:

The compressed data chunk consist of zlib compressed data. The checksum of the compressed data chunk is part the zlib compressed data format.

FTK Imager and EnCase 2 to 5 and linen 5 (EWF-E01)

Some aspects of this section are:

• The table section resides after the sectors section.
• It can be found in every segment file.
• The data chunks are no longer stored in this section but in the sectors section instead.
• The table2 section contains a mirror copy of the table section. In EWF-E01 it is always present.

The table section consists of:

• the table header
• an array of table entries
• the table footer

Table header

The sector table header is 24 bytes in size and consists of:

The table section can hold 16375 entries. A new table section should be created to hold more entries. Both FTK Imager and EnCase 5 can handle more than 16375, FTK 1 cannot. To contain more than 16375 chunks new sectors, table and table2 sections need to be created after the table2 section.

Table entry

The table entry is 4 bytes in size and consists of:

The most significant bit (MSB) in the chunk data offset indicates if the chunk is compressed (1) or uncompressed (0).

A chunk data offset points to the start of the chunk of media data, which resides in the preceding sectors section within the segment file. The offset contains a value relative to the start of the file.

Table footer

The table footer is 4 bytes in size and consists of:

EnCase 6 to 7 and linen 6 to 7 (EWF-E01)

Some aspects of this section are:

• Every segment file contains its own table section.
• It resides after the sectors section.
• The data chunks are no longer stored in this section but in the sectors section instead.
• The table2 section contains a mirror copy of the table section. In EWF-E01 it is always present.

The table section consists of:

• the table header
• an array of table entries
• the table footer

Table header

The sector table header is 24 bytes in size and consists of:

As of EnCase 6 the number of entries is no longer restricted to 16375 entries. The new limit seems to be 65534.

Table entry

The table entry is 4 bytes in size and consists of:

The most significant bit (MSB) in the chunk data offset indicates if the chunk is compressed (1) or uncompressed (0).

A chunk data offset points to the start of the chunk of media data, which resides in the preceding sectors section within the segment file. The offset contains a value relative to the table base offset.

In EnCase 6.7.1 the sectors section can be larger than 2048Mb. The table entries offsets are 31 bit values in EnCase6 the offset in a table entry value will actually use the full 32 bit if the 2048Mb has been exceeded. This behavior is no longer present in EnCase 6.8 so it is assumed to be a bug. Libewf currently assumes that the if the 31 bit value overflows the following chunks are uncompressed. This allows EnCase 6.7.1 faulty EWF files to be converted.

Table footer

The table footer is 4 bytes in size and consists of:

EnCase 6 to 7 (EWF-L01)

The EWF-L01 format uses the EnCase 6 to 7 (EWF-E01) table section specification.

Table2 section

The table2 section is identified in the section data type field as “table2”. Some aspects of this section are:

• Not defined in ASR Data - E01 Compression Format.
• Found in EWF-E01 in EnCase 2 to 7, or linen 5 to 7 or FTK Imager, EWF-L01 in EnCase 5 to 7. Not found in EnCase 1 (EWF-E01) or SMART (EWF-S01).
• Uses the same format as the table section.
• Resides directly after the table section.

FTK Imager and EnCase 2 to 7 and linen 5 to 7 (EWF-E01)

The table2 section contains a mirror copy of the table section. Probably intended for recovery purposes.

EnCase 5 to 7 (EWF-L01)

The EWF-L01 format uses the EWF-E01 table2 section specification.

Next section

The next section is identified in the section data type field as “next”. Some aspects of this section are:

• Defined in ASR Data - E01 Compression Format.
• Found in EWF-E01 in EnCase 1 to 7 or linen 5 to 7 or FTK Imager, EWF-L01 in EnCase 5 to 7, and SMART (EWF-S01)
• The last section within a segment other than the last segment file.
• The offset to the next section in the section header of the next section point to itself (the start of the next section).
• It should be the last section in a segment file, other than the last segment file.

SMART (EWF-S01)

It resides after the table or table2 section.

FTK Imager, EnCase and linen (EWF-E01)

It resides after the data section in a single segment file or for multiple segment files after the table2 section.

In the EnCase (EWF-E01) format the size in the section header is 0 instead of 76 (the size of the section header).

Note that FTK imager versions before 2.9 sets the section size to 76. At the moment it is unknown in which version this behavior was changed.

Ltypes section

The ltypes section is identifier in the section data type field as “ltypes”. Some aspects of this section are:

• Found in EWF-L01 in of EnCase 7
• Found in the last segment file after table2 section before tree section.

The additional ltypes section data is 6 bytes in size and consists of:

Ltree section

The ltree section is identifier in the section data type field as “ltree”. Some aspects of this section are:

• Found in EWF-L01 in of EnCase 5 to 7
• Found in the last segment file after ltypes section and before data section.

The ltree section consists of:

• ltree header
• ltree data

Ltree header

The ltree header is 48 bytes in size and consists of:

Ltree data

The ltree data string consists of an UTF-16 little-endian encoded string without byte order mark. The ltree data is not strict UTF-16 since it allows for unpaired surrogates, such as “U+d800” and “U+dc00”.

Other observed characteristics where the names in the ltree deviate from the original source:

• [U+0001-U+0008] were converted to U+00ba
• [U+0009, U+000a] were stripped
• [U+000b, U+000c] were converted to U+0020
• U+000d was converted to U+0002
• U+00ba remained the same

Note that this behavior could be related to EnCase as well and might not be specific for EWF-L01.

The ltree data string contains the following information:

The end of line character(s) is a newline (0x0a).

Records category

The rec category contains information about records.

The 1st line of the category contains the string “rec”.

The 2nd line of the category contains tab (0x09) separated type indicators.

The 3rd line of the category consist of the tab (0x09) separated values.

Permissions category

The perm category contains information about file permissions.

The 1st line of the category contains the string “perm”.

The 2nd line consists of the following 2 values:

The 3rd line of the category contains tab (0x09) separated type indicators. For more information see the sections below.

The remaining lines in the category consist of:

• category root entry
  • zero or more permissions group entries
    • zero or more permission entries

Each entry consist of 2 lines:

The 1st line of the category root entry consists of the following 2 values:

The 1st line of the permission group entry consists of the following 2 values:

The 1st line of the permission entry consists of the following 2 values:

Permission type indicators

Permission types

Access mask

Access mask seen in combination with property types 0, 1 and 6

Access mask seen in combination with property type 2

[0x001200a9] [R&X] [R] [Sync]
[0x001301bf] [M] [R&X] [R] [W] [Sync]
[0x001f01ff] [FC] [M] [R&X] [R] [W] [Sync]

Sources category

The srce category contains information about acquisition sources of the file entries.

TODO: describe what an acquisition source is in the context of EnCase.

The 1st line of the category contains the string “srce”.

The 2nd line consists of 2 values.

The 3rd line of the category contains tab (0x09) separated type indicators. For more information see the sections below.

The remaining lines in the category consist of:

• category root
  • zero or more source entries

Each entry consist of 2 lines:

The 1st line of the category root entry consists of the following 2 values:

The 1st line of the source entry consists of the following 2 values:

Source type indicators

The acquisition date and time is in the form of: “1142163845”, which is a POSIX epoch timestamp and represents the date: March 12 2006, 11:44:05.

If the “ha” value contains “00000000000000000000000000000000” this means the MD5 hash is not set. The same applies for the “sha” value when it contains “0000000000000000000000000000000000000000” the SHA1 has is not set.

If the “ma” value contains “000000000000” this means the MAC address is not set.

Drive type

Subjects category

The sub category contains information about TODO

TODO: describe what a subject is in the context of EnCase.

The 1st line of the category contains the string “sub”.

The 2nd line consists of 2 values.

The 3rd line of the category contains tab (0x09) separated type indicators. For more information see the sections below.

The remaining lines in the category consist of:

• category root
  • zero or more subject entries

Each entry consist of 2 lines:

The 1st line of the category root entry consists of the following 2 values:

The 1st line of the subject entry consists of the following 2 values:

Subject type indicators

File entries category

The entry category contains information about the file entries.

The 1st line of the category contains the string “entry”.

The 2nd line consists of 2 values.

The 3rd line of the category contains tab (0x09) separated type indicators. For more information see the sections below.

The remaining lines in the category consist of:

• category root
  • zero or more file entries
    • zero or more sub file entries
      • …

Each entry consist of 2 lines:

The 1st line of the category root entry consists of the following 2 values:

The 1st line of the file entry consists of the following 2 values:

EnCase 5 and 6 (EWF-L01) file entry type indicators

The creation, access and last written date and time are in the form of: “1142163845”, which is a POSIX epoch timestamp and represents the date: March 12 2006, 11:44:05.

The “ha” value (Hash) consist of a MD5 hash string when file entries are hashed. If the “ha” value contains “00000000000000000000000000000000” this means the MD5 hash is not set.

Ltree file entries

The ltree entries of files and directories consist of entries starting with: 0 followed by the number of sub file entries.

The entries of files and directories:

EnCase 7 (EWF-L01) file entry type indicators

If the “ha” value contains “00000000000000000000000000000000” this means the MD5 hash is not set. The same applies for the “sha” value when it contains “0000000000000000000000000000000000000000” the SHA1 has is not set.

File entry name

A file entry name (“n” value):

• can contain path segment separator characters like “\” and “/”
• uses the “MIDDLE DOT” Unicode character (U+00b7) as a (NTFS) alternative data stream (ADS) name seperator

Note that a regular “MIDDLE DOT” Unicode character will be encoded in the same way so no real way to reliably tell the difference.

An empty name has been observed to be represented as “NoName”.

Short name

The short name (“snh”) value contains 2 values:

For example: “13 FILE10~1.TXT”

Original extents

TODO: add some text

1 30a555b 30a6000 12011ae00 9008d7 3f 43 1 12011ae00 30a6000 120113 30a6 9008d7 18530

Ltree file entries

The ltree entries of files and directories consist of entries starting with: 26 followed by the number of sub file entries.

The entries of files and directories:

File entry flags

If 0x00002000 or 0x02000000 are not set the file entry is of type “File”.

If the sparse data flag is set:

• the data size should be 1 and data should consist of a single byte value.
• the data size should be equal to the file size and data should be the same.

If the duplicate data offset value is not set the single byte value in the data should be used to reconstruct the file data. E.g. if the file size is 4096 and the data contains the byte value 0x00 the resulting file should consists of 4096 x 0x00 byte values.

If the duplicate data offset value is set the single byte in the data is ignored and the duplicate data offset refers to the location where the data stored.

Binary extents value

The binary extents value contains 3 values separated by a space:

Unknown Offset Size

Where:

• unknown always is 1, could this be the number of extents?
• extent data offset, relative from the start of the media data
• extent data size

The offset and size are specified in hexadecimal values.

Note that the binary extents value contains only 1 value for the first single file entry.

Extended attributes value

The extended attributes value contains base-16 encoded data, which consists of:

• Extended attributes header (stored as an extended attribute)
• One or more extended attributes

Extended attributes header

The extended attributes header is 37 bytes in size and consists of:

Extended attribute

An extended attributes is of variable size and consists of:

TODO: complete section

Note that branch nodes are presuably used to group attributes, however these are not used consistently and are not shown by EnCase 7.

Map section

Some aspects of this section are:

• Found in EWF-L01 in of EnCase 7 (First seen in EnCase 7.4.1.10)
• Found in the last segment file after data section before done section.

The map consists of:

• map string
• map entries array

Map string

The map string consists of an UTF-16 little-endian encoded string without the UTF-16 endian byte order mark.

The map string contains the following information:

Map string values

The number of map entries should match the number of file entries in the ltree.

Map entry

A map entry is 24 bytes in size and consists of:

Session section

The session section is identifier in the section data type field as “session”. Some aspects of this section are:

• Not defined in ASR Data - E01 Compression Format.
• It is not found in SMART (EWF-S01) and FTK Imager (EWF-E01).
• It is found in EnCase 5 and 6 (EWF-E01) files.
• It is only added to the last segment file for images of optical disc (CD/DVD/BD) media.
• It is found after the data section and before the error2 section.

The session section data consists of:

• The session header
• The session entries array
• The session footer

Session header

The session header is 36 byte in size and consists of:

Session entry

A session entry is 32 byte in size and consists of:

EnCase stores audio tracks as 0 byte data with a sector size of 2048.

Note that for a CD the first session sector is stored as 16, although the actual session starts at sector 0. Could this value be overloaded to indicate the size of the reserved space between the start of the session and the ISO 9660 volume descriptor.

Session flags

Session footer

The session footer is 4 byte in size and consists of:

Error2 section

The error2 section is identifier in the section data type field as “error2”. Some aspects of this section are:

• Not defined in ASR Data - E01 Compression Format.
• It is not found in SMART (EWF-S01).
• It is found in, EnCase 3 to 7 and linen 5 to 7 (EWF-E01) files.
• It is only added to the last segment file when errors were encountered while reading the input.

TODO: check FTK Imager, EnCase 1 and 2 for presence of the error2 section.

It contains the sectors that have read errors. The sector where a read error occurred are filled with zero’s during acquiry by EnCase.

The error2 section data consists of:

• The error2 header
• The error2 entries array
• The error2 footer

Error2 header

The error2 header is 520 byte in size and consists of:

Error2 entry

An error2 entry is 8 byte in size and consists of:

Error2 footer

The error2 footer is 4 byte in size and consists of:

Digest section

The digest section is identified in the section data type field as “digest”. Some aspects of this section are:

• It is found in EnCase 6 to 7 files, as of EnCase 6.12 and linen 6.12 (EWF-E01).

The digest section contains a MD5 and/or SHA1 hash of the data within the chunks.

The digest section data is 80 byte in size and consists of:

Hash section

The hash section is identified in the section data type field as “hash”. Some aspects of this section are:

• Defined in ASR Data - E01 Compression Format.
• It is found in SMART (EWF-S01) and FTK Imager, EnCase 1 to 7 and linen 5 to 7 (EWF-E01) files.
• It is not found in EnCase 5 (EWF-L01).
• The hash section is optional, it does not need to be present. If it does it resides in the last segment file before the done section.

The hash section contains a MD5 hash of the data within the chunks.

The hash section data is 36 byte in size and consists of:

Notes

Observations regarding the unknown value:

• is zero in SMART
• is zero in EnCase 3 and below
• in EnCase 4 the first 4 bytes are 0, the next 8 bytes seem random, the last 4 bytes seem fixed
• in EnCase 5 and 6 the first 8 bytes seem random, the last 8 bytes equal the file header signature
• in linen 5 the first and last set of 4 bytes seem the same, the second set of 4 bytes seem to be random, the third set of 4 bytes seem to contain a piece of the file header signature
• in linen 6 the first and third set of 4 bytes seem random, the second and last set of 4 bytes seem to be the same
• EnCase5 seems to contain a GUID of the acquired device?

Test with EnCase 4 show that:

• The value does not equal the checksum of the media data
• Does not differentiate for the same media acquired within the same program session, using different formats, but differ for different media and different program sessions

Done section

The done section is identified in the section data type field as “done”. Some aspects of this section are:

• Defined in ASR Data - E01 Compression Format.
• It is found in SMART (EWF-S01), FTK Imager, EnCase 1 to 7 and linen 5 to 7 (EWF-E01) and EnCase 5 (EWF-L01) files.
• The done section is the last section within the last segment file.
• The offset to the next section in the section header of the done section point to itself (the start of the done section).
• It should be the last section in the last segment file.

SMART (EWF-S01)

It resides after the table or table2 section.

FTK Imager, EnCase and linen (EWF-E01)

It resides after the data section in a single segment file or for multiple segment files after the table2 section.

In the EnCase (EWF-E01) format the size in the section header is 0 instead of 76 (the size of the section header).

Note that FTK imager versions before 2.9 sets the section size to 76. At the moment it is unknown in which version this behavior was changed.

Incomplete section

The incomplete section is identified in the section data type field as “incomplete”.

This section is seen rarely. It was seen in an EnCase 6.13 (EWF-E01) file as the last last section within the last segment file. The incomplete section was preceded by a hash and digest section, although later in the set of EWF files another hash and digest section were defined.

It is currently assumed that the incomplete section indicates an incomplete image created using remote imaging. The incomplete section contains data but currently there is no indication what purpose the data has.

EWF-X

EWF-X (extended) is an experimental format to enhance the EWF format. EWF-X is based on the EWF-E01 format. EWF-X does not limit the table entries to 16375. EWF-X is not the same as version 2 of EWF.

TODO: add note about the table entry limit.

Sections

Additional sections provided in the EWF-X format are:

• xheader
• xhash

Xheader

The xheader section contains zlib compressed data containing XML data containing the header values.

<?xml version="1.0" encoding="UTF-8"?>
<xheader>
    <case_number>1</case_number>
    <description>Description</description>
    <examiner_name>John D.</examiner_name>
    <evidence_number>1.1</evidence_number>
    <notes>Just a floppy in my system</notes>
    <acquiry_operating_system>Linux</acquiry_operating_system>
    <acquiry_date>Sat Jan 20 18:32:08 2007 CET</acquiry_date>
    <acquiry_software>ewfacquire</acquiry_software>
    <acquiry_software_version>20070120</acquiry_software_version>
</xheader>

Xhash

The xhash section contains zlib compressed data containing XML data containing the hash values.

<?xml version="1.0" encoding="UTF-8"?>
<xhash>
    <md5>ae1ce8f5ac079d3ee93f97fe3792bda3</md5>
    <sha1>31a58f090460b92220d724b28eeb2838a1df6184</sha1>
</xhash>

GUID

EWF-X uses a random based version of the GUID

Corruption scenarios

This chapter contains several corruption scenarios that have been encountered “in the wild”.

Corrupt uncompressed chunk

TODO: add description

Corrupt compressed chunk

TODO: add description

DEFLATE uncompressed block data with copy of uncompressed data size of 0

Seen in combination with some firmware versions of Tableau TD3 forensic imager.

In this corruption scenarion the copy of uncompressed data size value of the DEFLATE uncompressed block data is set to 0 instead of the 1s complement of the uncompressed data size.

Libewf currently does not handle this corruption scenario.

Corrupt section header

TODO: add description

reading section header from file IO pool entry: 1 at offset: 415912423
type                      : table2
next offset               : 415978027
size                      : 65604
checksum                  : 0xf35f03e0
number of offsets         : 16375
base offset               : 0x00000000
checksum                  : 0x180d0137

reading section header from file IO pool entry: 1 at offset: 415978027
type                      : sectors
next offset               : 415978027
size                      : 0
checksum                  : 0x1ad00464

Corrupt table section

TODO: add description

Scenarios:

• with and with out table 2
• corruption in number of entries
• corruption in entry data

Corrupted segment file header

TODO: add description

Partial segment file

TODO: add description

Missing segment file(s)

TODO: add description

Dual image: section size versus offset

The section headers define both the next section offset and the size of the section. If an implementation reads only one of the two to determine the next section, a dual EWF image can be crafted that consists of two separate images including hashes.

Keramics will mark such an image as corrupted.

Table entries offset overflow

In EnCase 6.7.1 the sectors section can be larger than 2048 MiB. The table entries offsets are 31 bit values in EnCase6 the offset in a table entry value will actually use the full 32 bit if the 2048 MiB has been exceeded. This behavior is no longer present in EnCase 6.8 so it is assumed to be a bug.

Libewf currently assumes that the if the 31 bit value overflows the following chunks are uncompressed. This allows EnCase 6.7.1 faulty EWF files to be converted by Keramics.

Multiple incomplete segment file set identifiers

Although rare it can occur that a set of EWF image files changes its segment file set identifier. This was seen in an image created by EnCase 6.13, presumably using remote imaging. The image contained 3 different segment file set identifiers. The first changes after an incomplete section. The second one changed without any clear indication. The corresponding data section also changed in some extent e.g. compression method and media flags, the is physical flag being dropped. The change was consistent across multiple segment files. It is unlikely that deliberate manipulation is involved. EnCase considers the image as invalid.

Although with some tweaking of the individual segment file sets could be read. In this case the data read from the segment file sets was heavily corrupted. For now Keramics does not support reading multiple segment files sets from a single image, but this might change in the future.

AD encryption

As of version 2.8 FTK Imager supports “AD encryption”. Although the output file uses the EWF extensions the file actually is a AES-256 encrypted container. The EWF can be encrypted using a pass-phrase or a certificate.

TODO: link to format definition

References

• ASR Data - E01 Compression Format
• RFC4122 - A Universally Unique Identifier (UUID) URN Namespace