Can Unrar Extract Archives Encrypted with a Key File?

The standard unrar utility cannot natively extract archives using a key file because the RAR archive format exclusively supports password-based encryption. The RAR specification relies on password strings to derive encryption keys via key derivation functions, meaning there is no built-in mechanism or command-line switch within unrar to parse external key files directly. However, archives associated with a key file can still be extracted if the file contents or its cryptographic hash are passed to unrar as a standard password.

RAR Encryption Architecture

RAR archives (specifically RAR4 using AES-128 and RAR5 using AES-256) secure data using PBKDF2 (Password-Based Key Derivation Function 2). This algorithm takes an arbitrary-length text password and a cryptographic salt to generate the decryption key. Because the format is built specifically around this workflow:

  • The RAR format does not have a specification for public/private key pairs or detached symmetric key files.
  • The official command-line unrar utility only provides the -p[password] flag or standard interactive password prompts for decryption.
  • There are no native parameters (such as --key-file) to read binary or plain-text key files natively.

How Key Files Work with RAR Archives

When a backup system, script, or third-party tool claims to encrypt a RAR archive using a "key file," it almost always implements one of two methods:

  1. Direct Content as Password: The tool reads the key file's raw content (or a specific string inside it) and inputs that string directly into the password field when creating the archive.
  2. Cryptographic Hashing: The tool generates a hash (such as SHA-256 or MD5) of the key file and uses the resulting hexadecimal string as the archive password.

Extracting Key-File Protected Archives Using Unrar

To extract an archive protected this way, the key file must be converted into the expected password before or during the unrar execution.

If the Key File Contains the Plaintext Password

If the key file contains a raw password string, pass the file's contents directly to the -p switch via command substitution:

unrar x -p"$(cat /path/to/keyfile.txt)" archive.rar

If the Key File Is Hashed

If an automated process used a checksum of the key file as the password, compute the hash and feed it into unrar:

# Example using SHA-256
PASSWORD=$(sha256sum /path/to/keyfile.bin | awk '{print $1}')
unrar x -p"$PASSWORD" archive.rar

In summary, while unrar does not natively support key files, extraction is entirely possible by programmatically passing the file's data or hash to unrar's password mechanism.