• What's New in Version 5.00

    From Janis Kracht@1:2320/100 to All on Fri Oct 18 12:45:24 2013
    RAR - What's new in the latest version

    Version 5.00

    1. New RAR 5.0 archiving format. You can use -ma command line switch
    to create RAR 5.0 archives. By default RAR creates archives
    in 4.x format.

    2. Changes in RAR 5.0 compression algorithm:

    a) maximum compression dictionary size is increased up to 1 GB
    in 64 bit RAR. 32 bit RAR version can use up to 256 MB
    dictionary when creating an archive. Both 32 bit and 64 bit
    versions can unpack archives with any dictionary size,
    including 1 GB;

    b) default dictionary size for RAR 5.0 is 32 MB, typically resulting
    in higher compression ratio and lower speed than RAR 4.x 4 MB.
    You can use -md<size> switch to change this value;

    c) -md<size> switch syntax is modified to support larger dictionary
    sizes. Append 'k', 'm' and 'g' modifiers to specify the size
    in kilo-, mega- and gigabytes, like -md64m for 64 MB dictionary.
    If modifiers are not present, megabytes are assumed,
    so -md64m is equal to -md64;

    d) RAR 5.0 format includes Intel IA-32 executable and delta
    compression algorithms, but RAR 4.x text, audio, true color
    and Itanium algorithms are not supported. These excluded algorithms
    are not efficient for modern data types and hardware configurations;

    e) RAR 5.0 decompression can utilize several CPU cores.
    Though not to same extent as in compression algorithm,
    it improves the decompression speed on large files
    with poorly compressible data or when using BLAKE2 checksums.

    3. Changes in RAR 5.0 archive format:

    a) file times are stored as Coordinated Universal Time (UTC)
    instead of former local time, making file exchange among
    several time zones more straightforward;

    b) file names and archive comments use UTF-8 encoding.

    4. RAR 5.0 recovery record is based on Reed-Solomon error correction
    codes. If recovery record size is large enough, 5% and more,
    the new error correction scheme provides much higher resistance to
    multiple damages comparing to RAR 4.x recovery record.
    Smaller record, such as 1 - 2%, or less random damage type would
    result in less difference between 4.x and 5.0. For single continuous
    damage 4.x and 5.0 efficiency is about the same.

    Additionally to usual data erasures, the new recovery record
    is able to detect deletions and insertions of much larger size
    than in previous RAR versions. Maximum insertion size is several
    megabytes. Maximum deletion size depends on the damage type
    and in some cases can be as large as the recovery record size.

    Still, the best recovery performance and efficiency is achieved
    if no deletions and insertions are present, so all data including
    damaged sectors preserve their original positions. Thus, if you use
    some special software to copy an archive from damaged media,
    it is better to choose the mode, when damaged sectors are filled by
    zeroes or any other data instead of cutting them out completely
    from resulting file.

    RAR 5.0 recovery record is more resistant to damage of recovery record
    itself and can utilize a partially corrupt recovery record data.
    Note, though, that "Repair" command does not fix broken blocks
    in recovery record. Only file data are corrected. After successful
    archive repair, you may need to create a new recovery record
    for saved files.

    New recovery record is not based on 512 byte sectors anymore
    and incorporates more complicated data structures. So it is impossible
    to specify its size in sectors. For RAR 5.0 archives the parameter of
    -rr[N] switch and rr[N] command is always treated as a percent of
    archive size regardless of presence of % character. Typically N%
    recovery record can repair up to N% of continuously damaged data
    and increases the archive size by only slightly more than N%.
    Ability to fix multiple damages is proportional to N.

    We used "Screaming Fast Galois Field Arithmetic Using Intel
    SIMD Instructions" paper by James S. Plank, Kevin M. Greenan
    and Ethan L. Miller to improve Reed-Solomon coding performance.
    Also we are grateful to Artem Drobanov and Bulat Ziganshin
    for samples and ideas allowed to make Reed-Solomon coding
    more efficient.

    5. "Test" command verifies validity of RAR 5.0 recovery record.
    Recovery record is tested after processing all archived files.

    If corrupt archive contains the recovery record, it might be possible
    to repair it even if recovery record validity test is failed.
    "Repair" command attempts to utilize even a partially damaged
    recovery record. So treat the negative recovery record test result
    as a reason to re-create the archive if original files are still
    available, but not as a reason to avoid "Repair" command.

    6. Changes in RAR 5.0 encryption algorithm:

    a) encryption algorithm is changed from AES-128 to AES-256 in CBC mode.
    Key derivation function is based on PBKDF2 using HMAC-SHA256;

    b) special password verification value allows to detect most of
    wrong passwords without necessity to unpack the entire file;

    c) if archive headers are not encrypted ("Encrypt file names" option
    is off), file checksums for encrypted RAR 5.0 files are modified
    using a special password dependent algorithm, to make impossible
    guessing file contents based on checksums. Do not expect such
    encrypted file checksums to match usual CRC32 and BLAKE2 values.

    7. Switch -htb allows to utilize 256 bit length BLAKE2sp hash
    ( https://blake2.net ) instead of 32 bit CRC32 as a file checksum.

    While producing slightly larger archives, BLAKE2 can be used
    for file contents identification. If two files have the same
    BLAKE2 value, it practically guarantees that file contents
    is the same. BLAKE2 error detection property is also stronger
    than in much shorter CRC32.

    8. Features removed:

    a) authenticity verification feature did not provide the required
    level of reliability and was removed;

    b) switch -en (do not add "end of archive" block) is not supported
    by RAR 5.0 archives, which always have the end of archive block.
    This block helps RAR to safely skip external data like
    digital signatures appended to archive;

    c) old style extension based arcname.rNN volume names are not
    supported by RAR 5.0 archives, which use only arcname.partN.rar
    volume names;

    d) file comments are not supported anymore both in RAR 4.x
    and RAR 5.0 archives. Console RAR 'cf' command is removed.
    It does not affect the archive comment support, which is present
    in both versions of archive format and is not planned for removal.

    9. Switch -oh stores hard links as link instead of file. It is available
    only for RAR 5.0 archive format.

    10. Changes in recovery volume processing in RAR 5.0 archive format:

    a) maximum number of RAR+REV volumes in RAR 5.0 format is 65535
    instead of 255;

    b) recovery volume operations are faster than in RAR 4.x;

    c) additionally to recovery data, RAR 5.0 REV files also store
    service information such as checksums of protected RAR files.
    So they are slightly larger than RAR volumes which they protect.
    If you plan to copy individual RAR and REV files to some removable
    media, you need to take it into account and specify RAR volume
    size by a few kilobytes smaller than media size.

    11. Command line RAR returns the exit code 11 if it can detect that
    user entered a wrong password. This code can be returned only
    for RAR 5.0 archives. It is impossible to distinguish a wrong
    password and data damage for RAR 4.x archives.

    12. 'v' and 'l' commands display archived file names in the end of line,
    not in that beginning as before. Also some fields previously
    available in 'l' and 'v' output are now shown only by 'lt' and 'vt'.

    'vt' and 'lt' commands provide the detailed multiline information
    for every archived file.

    'vta' and 'lta' also include service headers into list.

    13. UTF-16 little endian encoding is used in RAR log file rar.log,
    so Unicode file names are stored in the log correctly.

    You can use -sc<charset>g switch to change the default log file
    encoding, such as -scag for native single byte encoding.

    14. Command line 'r' (repair) command can include an optional destpath\
    parameter defining the destination folder for repaired archive:

    rar r archive.rar destpath\

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