Fix SPAPI_E_AUTHENTICODE_PUBLISHER_NOT_TRUSTED 0x800F0243

You'll see this error when trying to install a driver or update Windows. The exact message is SPAPI_E_AUTHENTICODE_PUBLISHER_NOT_TRUSTED (0x800F0243). It usually happens right after plugging in a new printer, graphics card, or some USB device. Windows throws this error because it doesn't trust the digital signature on the driver file.

Why This Happens

Windows checks every driver's digital signature before letting it install. The signature proves the file came from a real company and hasn't been tampered with. But if the company's certificate expired, got revoked, or isn't in Windows' trusted store, you get this error. The culprit here is almost always an old or self-signed driver certificate. It's not malware - just outdated security.

Another common trigger is when Windows Update pushes a driver that's signed by a third-party vendor. That vendor's certificate might not be trusted by your specific Windows build. I've seen this a lot on Windows 10 version 22H2 and Windows 11 23H2.

Fix 1: Try Disabling Driver Signature Enforcement Temporarily

This is the quickest fix for testing. It doesn't solve the root cause, but it lets you install the driver right now.

1. Hold Shift and click Restart in the Start menu. This boots into recovery mode.
2. Go to Troubleshoot > Advanced options > Startup Settings.
3. Click Restart. After your PC restarts, press 7 to Disable driver signature enforcement.
4. Once Windows boots, install the driver again.

This only lasts until the next reboot. If the driver works, you'll need the permanent fix below.

Fix 2: Manually Trust the Publisher's Certificate

This is the real fix. You tell Windows to trust that specific publisher.

1. Right-click the driver file (usually a .inf or .cat file) and select Properties.
2. Go to the Digital Signatures tab.
3. Select the signature line and click Details.
4. In the new window, click View Certificate.
5. Click Install Certificate.
6. Choose Local Machine (you'll need admin rights).
7. Select Place all certificates in the following store, then click Browse.
8. Pick Trusted Publishers, then click OK and finish the wizard.

That adds the publisher to your trusted list. Try the driver install again - it should work now.

Fix 3: Update Windows and the Driver

Sometimes Windows itself needs a certificate update. Microsoft pushes these through cumulative updates.

1. Open Settings > Windows Update.
2. Click Check for updates. Install everything available.
3. After a restart, go to the device manufacturer's website and download their latest driver. Don't use Windows Update for this - get it direct from the vendor.
4. Install that driver.

I've fixed this exact issue on Dell laptops by grabbing the driver from Dell's support site instead of using the generic one from Windows Update.

Still Failing? Check These

If none of the above worked, here's what to look at:

• System clock - If the date or time is wrong, certificate checks fail. Right-click the clock and adjust it.
• Group Policy - Some IT-managed machines block untrusted certificates. Run gpedit.msc and check Computer Configuration > Windows Settings > Security Settings > Public Key Policies. If it's locked down, talk to your admin.
• Antivirus interference - Temporarily disable your antivirus (not Defender) and try the install again. I've seen Norton and McAfee block driver installs.
• Corrupt system files - Run sfc /scannow from an admin command prompt. If it finds issues, run DISM /Online /Cleanup-Image /RestoreHealth.

One more thing - don't bother with the "Driver Verifier" tool. It won't help here. It's for debugging kernel crashes, not signing errors.