.RAR File Format

Introduction

RAR 5.0 is the archive format that WinRAR has written by default since version 5.0 in 2013. It replaced the RAR 1.5 to 4.x format with a new header layout that uses variable-length numbers throughout, so file and archive sizes have no 4 GB limits. It also brought AES-256 encryption, optional BLAKE2sp hashes of the files, larger dictionaries and stronger recovery records. RARLAB publishes the header layout; the compression method is known only through the UnRAR source code.

Multi-volume archives are named name.part1.rar, name.part2.rar and so on.

Structure

After the signature the archive is a series of blocks. Each block header starts with a CRC-32 of the rest of the header, then the header size, the header type and the header flags, all but the CRC stored as variable-length integers (seven bits per byte, the top bit set when another byte follows). Flags say whether an extra area and a data area follow; a file’s compressed data is the data area of its file header.

A file header holds the file’s flags, unpacked size, attributes, an optional modification time and CRC-32, the compression information (version, solid flag, method and dictionary size), the host operating system and the name in UTF-8. Its extra area can add encryption settings, a BLAKE2sp hash, high-precision times, version numbers and link targets. A self-extracting archive has a program in front of the signature.

Variants

• RAR 5.0 archive (RAR5) – WinRAR’s current archive: CRC-32 block headers with variable-length numbers
• RAR 1.5 to 4.x archive (RAR4) – the older RAR format: blocks with a fixed 7-byte header and 16-bit CRC

Links