RAR version 3.00 - Technical information

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THE ARCHIVE FORMAT DESCRIBED BELOW IS ONLY VALID FOR VERSIONS SINCE 1.50

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RAR archive file format

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Archive file consists of variable length blocks. The order of these

blocks may vary, but the first block must be a marker block followed by

an archive header block.

Each block begins with the following fields:

HEAD_CRC 2 bytes CRC of total block or block part

HEAD_TYPE 1 byte Block type

HEAD_FLAGS 2 bytes Block flags

HEAD_SIZE 2 bytes Block size

ADD_SIZE 4 bytes Optional field - added block size

Field ADD_SIZE present only if (HEAD_FLAGS & 0x8000) != 0

Total block size is HEAD_SIZE if (HEAD_FLAGS & 0x8000) == 0

and HEAD_SIZE+ADD_SIZE if the field ADD_SIZE is present - when

(HEAD_FLAGS & 0x8000) != 0.

In each block the followings bits in HEAD_FLAGS have the same meaning:

0x4000 - if set, older RAR versions will ignore the block

and remove it when the archive is updated.

if clear, the block is copied to the new archive

file when the archive is updated;

0x8000 - if set, ADD_SIZE field is present and the full block

size is HEAD_SIZE+ADD_SIZE.

Declared block types:

HEAD_TYPE=0x72 marker block

HEAD_TYPE=0x73 archive header

HEAD_TYPE=0x74 file header

HEAD_TYPE=0x75 comment header

HEAD_TYPE=0x76 old style authenticity information

HEAD_TYPE=0x77 subblock

HEAD_TYPE=0x78 recovery record

HEAD_TYPE=0x79 authenticity information

Comment block is actually used only within other blocks and doesn't

exist separately.

Archive processing is made in the following manner:

1. Read and check marker block

2. Read archive header

3. Read or skip HEAD_SIZE-sizeof(MAIN_HEAD) bytes

4. If end of archive encountered then terminate archive processing,

else read 7 bytes into fields HEAD_CRC, HEAD_TYPE, HEAD_FLAGS,

HEAD_SIZE.

5. Check HEAD_TYPE.

if HEAD_TYPE==0x74

read file header ( first 7 bytes already read )

read or skip HEAD_SIZE-sizeof(FILE_HEAD) bytes

if (HEAD_FLAGS & 0x100)

read or skip HIGH_PACK_SIZE*0x100000000+PACK_SIZE bytes

else

read or skip PACK_SIZE bytes

else

read corresponding HEAD_TYPE block:

read HEAD_SIZE-7 bytes

if (HEAD_FLAGS & 0x8000)

read ADD_SIZE bytes

6. go to 4.

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Block Formats

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Marker block ( MARK_HEAD )

HEAD_CRC Always 0x6152

2 bytes

HEAD_TYPE Header type: 0x72

1 byte

HEAD_FLAGS Always 0x1a21

2 bytes

HEAD_SIZE Block size = 0x0007

2 bytes

The marker block is actually considered as a fixed byte

sequence: 0x52 0x61 0x72 0x21 0x1a 0x07 0x00

Archive header ( MAIN_HEAD )

HEAD_CRC CRC of fields HEAD_TYPE to RESERVED2

2 bytes

HEAD_TYPE Header type: 0x73

1 byte

HEAD_FLAGS Bit flags:

2 bytes

0x01 - Volume attribute (archive volume)

0x02 - Archive comment present

0x04 - Archive lock attribute

0x08 - Solid attribute (solid archive)

0x10 - New volume naming scheme ('volname.partN.rar')

0x20 - Authenticity information present

0x40 - Recovery record present

0x80 - Block headers are encrypted

other bits in HEAD_FLAGS are reserved for

internal use

HEAD_SIZE Archive header total size including archive comments

2 bytes

RESERVED1 Reserved

2 bytes

RESERVED2 Reserved

4 bytes

Comment block present if (HEAD_FLAGS & 0x02) != 0

File header (File in archive)

HEAD_CRC CRC of fields from HEAD_TYPE to FILEATTR

2 bytes and file name

HEAD_TYPE Header type: 0x74

1 byte

HEAD_FLAGS Bit flags:

2 bytes

0x01 - file continued from previous volume

0x02 - file continued in next volume

0x04 - file encrypted with password

0x08 - file comment present

0x10 - information from previous files is used (solid flag)

(for RAR 2.0 and later)

bits 7 6 5 (for RAR 2.0 and later)

0 0 0 - dictionary size 64 KB

0 0 1 - dictionary size 128 KB

0 1 0 - dictionary size 256 KB

0 1 1 - dictionary size 512 KB

1 0 0 - dictionary size 1024 KB

1 0 1 - dictionary size 2048 KB

1 1 0 - dictionary size 4096 KB

1 1 1 - file is directory

0x100 - HIGH_PACK_SIZE and HIGH_UNP_SIZE fields

are present. These fields are used to archive

only very large files (larger than 2Gb),

for smaller files these fields are absent.

0x200 - FILE_NAME contains both usual and encoded

Unicode name separated by zero. In this case

NAME_SIZE field is equal to the length

of usual name plus encoded Unicode name plus 1.

0x400 - the header contains additional 8 bytes

after the file name, which are required to

increase encryption security (so called 'salt').

0x800 - Version flag. It is an old file version,

a version number is appended to file name as ';n'.

0x8000 - this bit always is set, so the complete

block size is HEAD_SIZE + PACK_SIZE

(and plus HIGH_PACK_SIZE, if bit 0x100 is set)

HEAD_SIZE File header full size including file name and comments

2 bytes

PACK_SIZE Compressed file size

4 bytes

UNP_SIZE Uncompressed file size

4 bytes

HOST_OS Operating system used for archiving

1 byte 0 - MS DOS

1 - OS/2

2 - Win32

3 - Unix

4 - Mac OS

5 - BeOS

FILE_CRC File CRC

4 bytes

FTIME Date and time in standard MS DOS format

4 bytes

UNP_VER RAR version needed to extract file

1 byte

METHOD Packing method

1 byte

NAME_SIZE File name size

2 bytes

ATTR File attributes

4 bytes

HIGH_PACK_SIZE High 4 bytes of 64 bit value of compressed file size.

4 bytes Optional value, presents only if bit 0x100 in HEAD_FLAGS

is set.

HIGH_UNP_SIZE High 4 bytes of 64 bit value of uncompressed file size.

4 bytes Optional value, presents only if bit 0x100 in HEAD_FLAGS

is set.

FILE_NAME File name - string of NAME_SIZE bytes size

Comment block present if (HEAD_FLAGS & 0x08) != 0

Comment block

HEAD_CRC CRC of fields from HEAD_TYPE to COMM_CRC

2 bytes

HEAD_TYPE Header type: 0x75

1 byte

HEAD_FLAGS Bit flags

2 bytes

HEAD_SIZE Comment header size + comment size

2 bytes

UNP_SIZE Uncompressed comment size

2 bytes

UNP_VER RAR version needed to extract comment

1 byte

METHOD Packing method

1 byte

COMM_CRC Comment CRC

2 bytes

COMMENT Comment text

Extra info block

HEAD_CRC Block CRC

2 bytes

HEAD_TYPE Header type: 0x76

1 byte

HEAD_FLAGS Bit flags

2 bytes

HEAD_SIZE Total block size

2 bytes

INFO Other data

Subblock

An object in the archive (the block or header) can be followed

by a subblock. The subblock is dependent upon the main object.

Subblock can be erased or moved to a new version of the archive

when it is updated.

The subblock contains the following fields:

HEAD_CRC Block CRC

2 bytes

HEAD_TYPE Header type: 0x77

1 byte

HEAD_FLAGS Bit flags

2 bytes

(HEAD_FLAGS & 0x8000) == 1, because full

block size is HEAD_SIZE + DATA_SIZE

HEAD_SIZE Total block size

2 bytes

DATA_SIZE Total data size

4 bytes

SUB_TYPE Subblock type

2 bytes

RESERVED Must be 0

1 byte

Other Other fields depending on the subblock type

fields

OS/2 extended attributes subblock

HEAD_CRC Block CRC

2 bytes

HEAD_TYPE Header type: 0x77

1 byte

HEAD_FLAGS Bit flags

2 bytes

(HEAD_FLAGS & 0x8000) == 1, because full

block size is HEAD_SIZE + DATA_SIZE

HEAD_SIZE Total block size

2 bytes

DATA_SIZE Total data size (packed extended attributes size)

4 bytes

SUB_TYPE 0x100

2 bytes

RESERVED Must be 0

1 byte

UNP_SIZE Uncompressed extended attributes size

4 bytes

UNP_VER RAR version needed to extract extended attributes

1 byte

METHOD Packing method

1 byte

EA_CRC Extended attributes CRC

4 bytes

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Application notes

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1. To process an SFX archive you need to skip the SFX module searching

for the marker block in the archive. There is no marker block sequence (0x52

0x61 0x72 0x21 0x1a 0x07 0x00) in the SFX module itself.

2. The CRC is calculated using the standard polynomial 0xEDB88320. In

case the size of the CRC is less than 4 bytes, only the low order bytes

are used.

3. Packing method encoding:

0x30 - storing

0x31 - fastest compression

0x32 - fast compression

0x33 - normal compression

0x34 - good compression

0x35 - best compression

4. The RAR extraction version number is encoded as 10 * Major version

+ minor version.