RAR

RAR Archives (Roshal ARchive file format) is a proprietary format for storing information created by Eugene Roshal. The format is currently handled by Alexander Roshal, Eugene's brother.

Format

The file has the magic number of:

0x 52 61 72 21 1A 07 00

which is a break down of the following to describe an Archive Header:

• 0x6152 - HEAD_CRC
• 0x72 - HEAD_TYPE
• 0x1a21 - HEAD_FLAGS
• 0x0007 - HEAD_SIZE

Sub-formats

The RAR format is comprised of many sub-formats that have changed over the years. The different formats and their descriptions are as follows:

• 1.3 (Does not have the RAR! signature)
  • There is difficulty finding information regarding this sub-format. Please update if you know something.
• 1.5
  • Utilizes a proprietary compression method that is not available to the public.
  • Considered the root model of subsequent formats.
  • A detailed list of information can be found here.
• 2.0
  • Utilizes a proprietary compression method that is not available to the public.
• 3.0
  • Utilizes the PPMII and Lempel-Ziv (LZSS)] algorithms.
  • Encryption now uses cipher block chaining (CBC) instead of Advanced Encryption Standard (AES).

Software

This only way to create a RAR file is using the Winrar software. There are several implementations of the process to open a RAR file (commonly known as the "unrar" process). Some of them are:

unrarLib

• RAR file unarchiver written in C
• Easy implementation with a header file and the source code file
• Information Link

WinRAR

• Only software that can create and open a RAR file
• Distributed by a proprietary license
• WinRAR executable for Windows

UnRAR

• Created by Eugene Roshal for opening up RAR files only
• May not be used to reverse engineer the RAR file format and create RAR files
• Source code provided for people to implement/integrate methods of opening RAR files
• Additionally, implementations of UnRAR are available for a plethora of operating systems
• Download Link

The Unarchiver

• Utility made for Mac OSX to open a multitude of files, including RAR files
• Very handy for dealing with multiple file types
• Source Code Download
• Information Website

7-Zip

• Utility made for Windows applications to open a multitude of files, including RAR files
• Download Link

There is a lot more software to open RAR files, but have been omitted due to redundancy.

See Also

• Wikipedia: RAR
• RAR file Format Information