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Can a Simple Registry Change Finally Fix Your Smart Card and Restore Access After the October Update?
A security update released by Microsoft in October 2025 has created significant problems for users who rely on smart cards for authentication. If you have recently updated your Windows computer and can no longer use your smart card to log in or sign documents, you are not alone. This issue stems from a change intended to improve security, but it has unintentionally disrupted access for many.
Microsoft has formally recognized the problem. The good news is that there are clear steps you can take to identify if you are affected and a specific workaround to restore your smart card’s functionality. This guide will walk you through understanding the issue, diagnosing it on your system, and applying the recommended temporary solution.
Understanding the October 2025 Update Problem
On October 14, 2025, Microsoft distributed security updates across its supported Windows client and server platforms. These updates are a routine part of maintaining a secure system. However, the update designated as KB5066835 for Windows 11 versions 24H2 and 25H2 contained a fundamental change to how Windows handles cryptography. This change is the root cause of the current smart card issues.
Many individuals and organizations use smart cards as a highly secure method for verifying identity. You might use one to:
- Log into your work computer or network.
- Access secure websites or applications.
- Digitally sign official documents to prove their authenticity.
After installing the October update, users began reporting that their systems failed to recognize their smart cards. The most common symptoms include:
- Applications that require a smart card fail to launch or produce errors.
- Attempts to digitally sign a document result in a failure message.
- You might see specific error messages, such as “Invalid provider type” or “CryptAcquireCertificatePrivateKey errors,” when a program tries to access the smart card.
- In some cases, 32-bit applications are completely unable to detect the smart card, even if the system sees the physical card reader.
The problem originates from a security enhancement where Microsoft shifted from an older technology, Cryptographic Service Providers (CSP), to a more modern and secure one known as Key Storage Providers (KSP). Think of it like changing the locks on a door. KSP is a more advanced lock, but some smart cards and applications were still designed to work with the old CSP key. The update forced the system to use the new lock, but it did not properly account for all the old keys still in circulation, effectively locking users out.
Which Systems Are Affected by the Smart Card Issue?
This issue is widespread and impacts nearly all currently supported versions of Windows. If your system receives automatic updates, it is likely affected. Microsoft has confirmed the problem exists on the following operating systems:
Client Operating Systems:
- Windows 11, versions 24H2 and 25H2
- Windows 11, versions 22H2 and 23H2
- Windows 10, version 22H2
Server Operating Systems:
- Windows Server 2025
- Windows Server, version 23H2
- Windows Server 2022
- Windows Server 2019
- Windows Server 2016
- Windows Server 2012 R2
- Windows Server 2012
How to Confirm if Your System Is Affected
Before making any changes to your system, you can verify if the smart card issue applies to you. Windows creates a log of system events, and a specific warning logged before the update is a strong indicator of the problem. You can find this warning by using the Event Viewer.
- Click the Start button or press the Windows key.
- Type “Event Viewer” into the search bar and select the app to open it.
- On the left-hand panel, expand the Windows Logs category and click on System.
- Your screen will populate with a long list of system events. To find the relevant one, click on Filter Current Log… in the Actions panel on the right side.
- A new window will appear. In the field labeled <All Event IDs>, type the number 624. Click OK.
- The log will now only show events with that ID. Look for an entry with the following text in its details: “Audit: This system uses CAPI for RSA cryptography operations.“
If you find this event logged on your system before October 14, 2025, it means your computer was using the older CSP method that the update disrupted. You are very likely affected by this smart card authentication issue.
How to Fix the Smart Card Problem with a Registry Edit
Microsoft has provided a workaround that involves editing the Windows Registry. This change tells your system to allow the older CSP method to function again, restoring compatibility with your smart card.
Important: Editing the Windows Registry can cause serious problems if done incorrectly. It is highly recommended that you back up your registry before proceeding. To do this, open the Registry Editor, click File in the top menu, and select Export. Save the file to a safe location.
Follow these steps carefully to apply the fix:
- Press the Windows + R at the same time to open the Run dialog box.
- Type regedit into the box and press Ctrl + Shift + Enter to open the Registry Editor with administrator privileges. You may need to approve a User Account Control prompt.
- The Registry Editor will open. At the top, there is an address bar. Copy and paste the following path into the bar and press Enter:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\Calais - This will take you directly to the correct location. In the main window on the right, look for a value named DisableCapiOverrideForRSA.
- Double-click on DisableCapiOverrideForRSA to edit it.
- Change the number in the Value data field to 0.
- Click OK to save the change.
- Close the Registry Editor and restart your computer.
After your computer restarts, the workaround will be active. Try using your smart card again. Your ability to log in, access applications, and sign documents should now be restored.
This registry modification acts as a compatibility switch. It is a temporary fix, not a permanent one. Microsoft is expected to release a future security update that resolves the conflict properly. Until then, this workaround allows you and your organization to continue operating without disruption. Administrators should consider testing this fix on a small number of computers before deploying it across an entire network.