Fix SHA-256 Signature Errors with a PIV Card in Acrobat on macOS
Question details
The user needs to troubleshoot an error in Acrobat on macOS indicating that the signature device does not support SHA-256 when applying a digital signature using an Identiv Cloud 2700R PIV reader.
- Product
- Adobe Acrobat
- Device & OS
- macOS
- Scenario
- Applying a digital signature using a hardware PIV smart card reader.
- Observed behavior
- A warning appears stating that the signature device does not support SHA-256, which prevents the digital signature from being applied successfully.
Ensure your macOS is fully updated and that your PIV card reader is securely connected directly to a USB port on your Mac, avoiding external USB hubs if possible.
Update Mac Reader Drivers and PIV Middleware
Ensure that your smart card reader drivers and middleware software are up to date and correctly configured to support SHA-256 hashing on macOS.
Digital signature errors involving SHA-256 on macOS are most commonly caused by outdated PIV middleware or card reader drivers that fail to communicate the card's hashing capabilities to Adobe Acrobat.
Visit your smart card reader manufacturer's official website (e.g., Identiv) to download and install the latest macOS driver specifically designed for your reader model (like the Cloud 2700R).
Download and install the latest version of your required PIV middleware (such as OpenSC or your vendor-specific PKI client). Make sure the release notes explicitly mention SHA-256 signing support for macOS.
Open Adobe Acrobat, navigate to 'Acrobat' > 'Preferences' > 'Signatures' in the top menu bar. Click 'More' under 'Identities & Trusted Certificates', and verify that your updated PKCS#11 module or token is correctly loaded and attached.
Verify Certificate Selection and OS Compatibility
Confirm you are selecting the correct digital certificate and isolate whether the issue is strictly limited to macOS.
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Frequently Asked Questions
Why does Acrobat say my signature device doesn't support SHA-256?
This error usually occurs when the smart card middleware or macOS driver installed on your system does not correctly communicate the SHA-256 hashing capability of your PIV card to Adobe Acrobat.
How do I know if my PIV card supports SHA-256?
Most modern PIV cards support SHA-256. You can verify this by viewing the certificate properties in your macOS Keychain Access utility or your specific middleware management tool to check the signature hash algorithm.
What is PIV middleware and why do I need it?
PIV middleware is the software layer that translates communication between macOS, the physical smart card reader, and applications like Acrobat. Without updated middleware, your Mac cannot utilize the cryptographic functions of the smart card.
Will using a different PDF reader fix the PIV card error on Mac?
It might not. Other PDF readers rely on the same underlying macOS smart card drivers and middleware. If those underlying system components are outdated, the SHA-256 error will likely persist across different applications.
