Sign a PDF file on an IIS server using a SmartCard from the client

Question

This is my problem:

I want to sign a file located on the IIS server with an SSL certificate that is instead located on the client computer.

How can I open the store, choose a certificate and then use it on the server to sign the PDF?

I use Asp.Net, Visual Studio 2019, .Net 4.8.

Any help is greatly appreciated

Answer 1

Signing a PDF file on an IIS server using a client's SSL certificate (SmartCard) involves a combination of client-side and server-side processes. Below is a high-level overview of the steps involved in achieving this:

Client-Side (Browser):

Detect SmartCard: Use JavaScript in your web page to detect the presence of a SmartCard and retrieve information about available certificates. You can use libraries like window.crypto or WebCryptoAPI to access the user's certificates.

Select Certificate: Allow the user to select the appropriate certificate for signing. You can provide a UI for the user to choose from the available certificates on their SmartCard.

Sign Data: Use JavaScript to sign the PDF document data with the selected certificate. This may involve using a library like PKIjs or others that provide cryptographic functions for handling PKCS#7 signatures.

Send Signature to Server: Once the data is signed, send the signature to the server for further processing.

Server-Side (ASP.NET):

Receive Signature: In your ASP.NET application, receive the signed data (signature) from the client.

Verify Signature: Use the public key associated with the user's certificate to verify the signature. You may need to extract the public key from the certificate and use it for verification.

Apply Signature to PDF: Use a PDF library like iTextSharp to apply the verified signature to the PDF file on the server.

Serve Signed PDF: Return the signed PDF file to the client or provide a download link.

Additional Considerations:

Security: Ensure that your application follows security best practices. Protect sensitive operations, validate input, and secure communication channels.

User Authentication: Consider implementing user authentication mechanisms to ensure that only authorized users can perform signing operations.

SmartCard Middleware: Ensure that the client's browser has the necessary SmartCard middleware installed to interact with the SmartCard.

Cross-Browser Compatibility: Be aware that different browsers may have different implementations for accessing certificates and cryptographic operations. Test your solution across major browsers.

Code Signing: In some cases, you may need to explore code signing solutions, especially if you want to sign the PDF on the client side.

It's important to note that interacting with client certificates from a web application involves considerations related to security, user experience, and compatibility. Always test thoroughly and consider consulting with a security expert if needed.