How to Verify Arch Linux ISO Signature Before Installation

When installing an operating system like Arch Linux, ensuring the integrity and authenticity of the installation media is a crucial first step. Verifying the ISO file before installation prevents tampering, corruption, or man-in-the-middle attacks that could compromise your system. In this article, we’ll walk through how to verify the Arch Linux ISO signature on Windows, macOS, and Linux.

Whether you’re a security-conscious user or a beginner looking to do things right from the start, this guide will help you confidently validate your Arch ISO.

Why Verifying the ISO Matters

When you download the Arch Linux ISO from a mirror, you’re downloading a file that is often hundreds of megabytes in size. If even one byte is altered—whether through corruption during download or due to a malicious actor—the entire file could be rendered unreliable or dangerous.

To counter this, the Arch team signs their ISO files using PGP (Pretty Good Privacy). These digital signatures can be verified using tools available on most operating systems. By checking these signatures, you:

• Confirm that the ISO file hasn’t been tampered with.
• Verify that it was produced by a trusted source.
• Ensure the file hasn’t been corrupted in transit.

What You Need

To verify an Arch Linux ISO file, you’ll need:

1. The ISO file itself (e.g., archlinux-2025.04.01-x86_64.iso)
2. The corresponding .sig signature file (e.g., archlinux-2025.04.01-x86_64.iso.sig)
3. A PGP tool (e.g., GnuPG)
4. The official Arch Linux signing key

Step 1: Download the Necessary Files

Head to the official Arch Linux download page or any of its trusted mirrors:

• https://archlinux.org/download/

Download the following:

• The ISO file
• The .sig file (found next to the ISO)

Example:

archlinux-2025.04.01-x86_64.iso
archlinux-2025.04.01-x86_64.iso.sig

Step 2: Get the Arch ISO Signing Key

The Arch ISO is signed by Pierre Schmitz, a long-time Arch developer. His key ID is:

Key ID: 0x9741E8AC
Fingerprint:  040D 0A18 7F29 3DCE 4652  F4C0 1A37 D8CB 9741 E8AC

This key is available on most public keyservers and can be retrieved using your platform’s PGP tool.

Verifying on Linux

Step 1: Install GnuPG (if not already installed)

Most Linux distributions come with gpg, the GNU Privacy Guard tool.

To check:

gpg --version

If not installed, you can install it with your package manager:

sudo apt install gnupg    # Debian/Ubuntu
sudo pacman -S gnupg      # Arch
sudo dnf install gnupg    # Fedora

Step 2: Import the Signing Key

gpg --keyserver hkps://keyserver.ubuntu.com --recv-keys 1A37D8CB9741E8AC

Alternatively, use the full fingerprint:

gpg --keyserver hkps://keyserver.ubuntu.com --recv-keys 040D0A187F293DCE4652F4C01A37D8CB9741E8AC

Step 3: Verify the ISO Signature

Assuming both archlinux-*.iso and archlinux-*.iso.sig are in the same folder:

gpg --verify archlinux-2025.04.01-x86_64.iso.sig

If successful, you’ll see:

gpg: Good signature from "Pierre Schmitz <pierre@archlinux.de>" [unknown]

If it says the key is not trusted, that’s expected. You can manually trust it or just confirm the fingerprint matches the official one.

Verifying on macOS

Step 1: Install GnuPG

macOS doesn’t ship with GPG by default. Use Homebrew to install it:

brew install gnupg

Step 2: Import the Signing Key

gpg --keyserver hkps://keyserver.ubuntu.com --recv-keys 1A37D8CB9741E8AC

Step 3: Verify the ISO Signature

Navigate to the folder with the ISO and signature:

cd ~/Downloads
gpg --verify archlinux-2025.04.01-x86_64.iso.sig

You should see a message indicating a good signature from Pierre Schmitz.

Verifying on Windows

Step 1: Install Gpg4win

1. Download and install Gpg4win from https://gpg4win.org.
2. During installation, ensure Kleopatra (GUI for managing keys) and GnuPG are selected.

Step 2: Import the Signing Key

Using Kleopatra (GUI):

1. Open Kleopatra.
2. Go to File > Lookup on Server.
3. Enter 1A37D8CB9741E8AC or paste the full fingerprint.
4. Click Import.

Or using command line:

Open Command Prompt or PowerShell and run:

gpg --keyserver hkps://keyserver.ubuntu.com --recv-keys 1A37D8CB9741E8AC

Step 3: Verify the Signature

Still using the command line (assuming the files are in Downloads):

cd $HOME\Downloads
gpg --verify archlinux-2025.04.01-x86_64.iso.sig

A successful output will say:

gpg: Good signature from "Pierre Schmitz <pierre@archlinux.de>"

If you get a warning about the key not being certified, it’s normal. Just manually check the key fingerprint.

Troubleshooting Verification Issues

1. Signature Does Not Match

If you see an error like:

gpg: BAD signature

This means the ISO file doesn’t match the signature. Possible causes:

• The ISO was corrupted during download.
• The ISO file doesn’t match the .sig file.
• You downloaded the files from a malicious source.

Solution: Re-download both files from the official Arch Linux website or a verified mirror.

2. No Public Key

If you get:

gpg: Can't check signature: No public key

It means you need to import the Arch signing key.

3. Untrusted Signature

Even if the signature is valid, GPG might still warn you that the key is not trusted. That’s because GPG uses a web-of-trust model. You can safely ignore this if the fingerprint matches the one published by Arch Linux.

To check the key’s fingerprint:

gpg --fingerprint 1A37D8CB9741E8AC

Match it against the official one:

040D 0A18 7F29 3DCE 4652  F4C0 1A37 D8CB 9741 E8AC

Tips for Advanced Users

• If you’re automating ISO downloads, consider scripting the key import and signature check steps.
• Always use https and verify SHA256 sums as a secondary check.
• Periodically check that the Arch team hasn’t rotated their signing key.

Conclusion

Verifying the Arch Linux ISO signature before installation is a vital step that takes only a few minutes but provides assurance that your installation media is safe and genuine. Whether you use Linux, macOS, or Windows, the process involves:

1. Installing GnuPG or its equivalent.
2. Importing the Arch ISO signing key.
3. Checking the .sig file against the downloaded ISO.

This small habit protects you from tampered or corrupted files and helps you follow best practices in system security. Especially when you’re about to install an OS like Arch Linux, starting off with a clean, trusted ISO sets the foundation for a secure and stable system.