RAR Files

What is a .RAR file?

RAR (.RAR) is an archived and possibly compressed data container of RAR data archiving format made by the Russian programmer, Eugene Roshal. Tools for RAR include WinRAR, RAR and UnRAR, which are mainly provided by RARLAB Inc. There could be one or many files and directories with names, timestamps, file attributes, compressed data streams and other possible components like comment, checksum and encryption within one archived file.

RAR files usually exist in software downloaded, games/downloads of mods, medias collected into collection, email attachment as well multi part upload on file sharing networks. Latest formats are of RAR 5.0 format, released with WinRAR 5.0 version while plenty others still have signature of old versions and could also be extracted; rare archives from old format RAR 1.3 that also could be recognized as .RAR extension are quite ancient archive format.

Part files could use names like archive.part1.rar, archive.part2.rar, or older archive.r00/archive.r01; open/extract from archive.part1.rar. If needed check the version from the beginning bytes - if it starts from bytes “52 61 72 21 1A 07 01 00” it means RAR 5.0; if it starts from the beginning “52 61 72 21 1A 07 00”, then RAR 1.5-4.x; if it is like “52 45 7E 5E”, RAR 1.3”.

How to open a .RAR file

Technical details

RAR is actually a binary format container and thus is not ZIP-compatible in addition to its use as archive container. The structure of the RAR starts with the magic number on the offset 0, then proceeds further with the list of blocks' headers and compressions streams.

The current 5.0 version utilizes the 52 61 72 21 1A 07 01 00, while the legacy ones, 1.5-4.x versions utilized the bytes 52 61 72 21 1A 07 00 as the start of the signature of the RAR file. One of the very first RAR 1.3 signatures was the following one - 52 45 7E 5E.

Internally, RAR structure is header-based - each of those describes some kind of data such as metadata, content file or a stream, comments or services-related information. The latest 5.0 version introduced its header and checksum system as well as opposed to the old RARs 4.x ones. The RAR allows creating the common normal archives as well as "solid" archives (one compressed stream for several files).

Several generations of RAR developed different compression techniques and methods: 5.0 allows to make use of substantially larger dictionaries up to hundreds of MiB and works using the parameters different from older 4.x line, and stores Unicode file names and high-precision timestamps. In additions, the modern RAR contains service headers, possible archive comments, file metadata, and the file BLAKE2sp checksums. Encryption in case of the modern RAR makes use of AES-256, using derived keys.

File data of RAR file can be encrypted alone with the archive or even with the possibility for encryption of the header too, what would also make filenames be encrypted as well. RAR files allow making several-volume RARs; each volume contains specific volume data and extraction usually requires access to the entire series or recovery data for making up for any loss or damage within RAR. There were also RAR recovery records and possibly the recovery volumes.

Some usual mime types for RAR archives are application/vnd.rar for the 5.0 one and application/x-rar-compressed. RAR archive size can vary from small metadata-only files up to gigabytes for the split RAR sets.

How to convert .RAR files

By “common conversion” we mean the process of retrieving the original files. There are several software that supports extraction of files from RAR archives (for example WinRAR, The Unarchiver or Unrar) and they don’t change their content. Provided that everything goes right, i.e., RAR archive is valid (hasn’t been tampered with by someone), has a passcode if any and we do have one - conversion results in the same files inside as were compressed originally. In windows or under linux unrar x archive.rar or 7z x archive.rar should be used. When dealing with protected archive the password does not get deleted after conversion, but must be provided at opening stage.

The easiest way to make a Zip file out of rar on different platforms will be to extract the RAR first using WinRAR, 7-Zip (or others mentioned) program and than use zip compression utilities provided. For 7z we should extract first and than make compressed copy 7z a archive.7z files... . They could help reducing size though will replace RAR metadata and volume structure. To prepare TAR.GZ or TAR.XZ archives we should make unpacking/repacking through tar/gzip /xz. Attributes of Windows and RAR recovery records won’t be saved. We also need to have entire Split RAR set ready to go.

It is worth noting also that there would be no point in changing part files names. We could extract and rename but could not merge them together. We also won’t get RAR comment, solid blocks or other information like old authenticity checks or recovery record data after conversion. And media/document archives need conversion of their files directly.

Common problems and fixes

An "Unexpected end of archive," or "Unexpected end of data," is caused by incomplete files, and for multi-parts it could mean one of the files is missing or corrupt. The solution would then be to download again all archive parts, save it in one folder, test with winrar or unrar t archive.rar before extracting.

"Checksum error," or "CRC failed," indicates the compressed files are corrupted, while in the case of a passworded RAR the same messages could simply signify entering the incorrect password. Try entering the password precisely the way it was written, take care with your keyboard language settings, and if there is a recover record present, use winrar repair command or get it from elsewhere.

"The archive is either in unknown format or damaged." It could simply indicate an incorrect format or damaged file since it is possible to have something non-related or even a renamed Zip, that was incorrectly interpreted and downloaded. Magic bytes located at file offset 0 must begin with 52 61 72 21 1A 07 01 00 for 5.0 RARs and 52 61 72 21 1A 07 00 for RARs 1.5-4.x. You can try testing with WinRar and UnRar in original form.

"You need to start extraction from a previous volume," could result from opening a continuation file (.part2.rar, .r00, etc.), instead of the base archive file (.rar, .part1.rar). "Next volume is required" would mean missing or renamed continuation files.

"Cannot open encrypted archive. Wrong password?" Header encryption hides names from being shown, but password entered needs to be exactly the same as the one used for compression. Slow performance can be associated with solid archives, dictionary sizes greater than RAM, antivirus scans, and network drives where copying the file to your computer and checking your disk free space would be advised. Mac and Linux users would require unrar/Unar/P7zip installation.

Security considerations

The only role of a .rar file is that of a wrapper, but it might be quite malicious in nature, containing EXE installers, some kind of scripts or macros in Office files, links, or even packed archive files. There were found quite significant vulnerabilities of archive parsers with regards to WinRAR, UNACE and others. So make sure you are having the most recent version of WinRAR, 7-Zip, UnRAR, and all their mobile companions installed. Newer decompressors tend to prevent directory traversal problems and accept relative pathes only; nevertheless, all suspicious archives better be extracted in a fresh directory. Any RAR archive is able to store the filename, comments, time stamps, names of directories, names of users present in paths and content of various kinds, thus, leaking potentially sensitive info. Encryption makes an archive file unreadable and header encryption will be hiding even file names; nevertheless, poor passwords remain exposed to brute force attack offline.

History and versions

RAR technology emerged in 1993 under Eugene Roshal's development and the abbreviated form for the name Roshal ARchive became very popular when it appeared as one of the main formats used in both DOS and Windows environments via RAR and then WinRAR, owing to good results in terms of compression, multi-volume archives, recovery record capacity, etc.

RAR 1.5 used the signature 52 61 72 21 1A 07 00 and this signature stayed in use through 4.x and replaced the earlier signature 52 45 7E 5E from RAR versions 1.3 times. As to the years' 2000, the widespread use of WinRAR 3.x had led to the creation of Unicode filename capability, solid compression, encryption and handling of large files (as compared with many ZIP utilities of those times).

RAR 5.0 was produced in tandem with WinRAR 5.0 in 2013 and changed the above-presented signature into 52 61 72 21 1A 07 01 00 and redesigned other header data besides enhanced checksums and encryption. Although RARLAB provides technical articles for recognition and unarchiving of RAR archives but RAR format has not became the open standards. For example, there is UnRAR source only for decompression under very narrow license that hinders independent creation of compressors and limits further development of format.

Related formats

ZIP (.zip) is the closest mainstream rival to RAR (.rar). Almost any operating system supports opening ZIP archive using the standard file manager, the standard of which - the document called APPNOTE - is openly published. The performance in compression and recovery for ZIP archive will be less effective than that of RAR, especially when considering a large multi-file data set. 7Z (.7z) format archive uses the format of the open source utility 7-zip that utilizes LZMA and LZMA2 types of compression besides AES encryption. 7Z provides good support for the open tools, better compression rate and security, but it's less supported at the operating system level. TAR (.tar), TAR.GZ (.tar.gz, .tgz), and TAR.XZ are commonly used formats on Unix and Linux systems, the metadata for the file are saved using this method after which the data stream is compressed using gzip/xz. These formats provide no recovery like rar one provides. CAB (.cab) format is used by Microsoft in case of creation installers for Windows OS. ISO (.iso) is a disc image, it's not an archive file so RAR archive should be unpacked before mounting.