How unrar Handles RAR Authenticity Verification

This article explains how the unrar utility processes archives containing RAR Authenticity Verification (AV) data. Modern versions of unrar completely ignore or bypass legacy Authenticity Verification records, extracting the contained files normally without attempting cryptographic validation. Because RARLab officially deprecated and removed the AV feature due to security and architectural obsolescence, the presence of an AV signature has no enforcement mechanism in current command-line extraction workflows.

What Was RAR Authenticity Verification?

Authenticity Verification was a proprietary feature introduced in early versions of the RAR format (notably RAR 2.x and early 3.x). When registered users created archives, WinRAR/RAR could embed an electronic signature containing the creator's name, creation timestamp, and archive integrity data.

The intended purpose was to guarantee that the archive had not been modified by a third party after creation. If any byte inside the archive changed, extraction tools with AV checking enabled were supposed to warn the user or halt extraction.

How Modern unrar Handles AV Archives

In modern versions of unrar (covering both the proprietary freeware tool and the open-source unrar source package maintained by RARLab), the handling of Authenticity Verification is straightforward:

  1. Header Skipping: Modern unrar treats the legacy Authenticity Verification block as an obsolete or informational header. When parsing the archive headers, the utility reads past the AV block without validating its cryptographic authenticity.
  2. Standard Extraction: Archive contents are extracted normally, provided the core data stream and file checksums (CRC32 or BLAKE2sp) remain intact.
  3. No Cryptographic Enforcement: unrar will not prevent a user from extracting files if the AV record is invalid, stripped, or modified. Modern command-line builds do not query or enforce license keys or public/private key pairs related to old AV signatures.

Historical Behavior in Older unrar Versions

In legacy versions of unrar (prior to RAR 5.0 and older 3.x/4.x releases):

  • Verification Display: Running unrar v or extracting an AV-signed archive would display the embedded creator information (e.g., "Authenticity verification: Archive created by [Name]").
  • Failure Warnings: If an archive was tampered with, older unrar builds would print an error such as AV failed or Authenticity verification failed.
  • Disabling Verification: Users could explicitly bypass checks using the -av- switch on the command line to force extraction even if an archive had broken or missing AV data.

Why the Feature Was Phased Out

RARLab phased out Authenticity Verification across the RAR ecosystem for several reasons:

  • Weak Cryptographic Design: The legacy AV system relied on older, proprietary cryptographic methods that did not meet modern security standards.
  • Format Evolution: The introduction of the RAR 5.0 format replaced obsolete metadata structures with more robust, standard mechanisms.
  • Redundancy: Modern archive distribution relies on external cryptographic signing methods (such as GPG/PGP signatures, X.509 code signing, or HTTPS transport security) rather than proprietary in-archive signature blocks.

Verifying Archive Integrity Today

Because unrar no longer verifies archive authenticity via AV blocks, verification relies on other mechanisms:

  • Data Corruption Checks: unrar t archive.rar tests archive integrity by validating each file against its internal CRC32 or modern BLAKE2sp cryptographic checksum. This detects transmission errors or disk corruption, though not intentional tampering by an attacker with access to repackage the archive.
  • External Signatures: To verify identity and prevent tampering, distribution workflows generate external detached signatures (such as .asc or .sig files) that can be verified using tools like gpg prior to invoking unrar.