Smart Card Document Security

TL;DR

Yes, a smart card with a PKI (Public Key Infrastructure) certificate can be used to protect a document through digital signatures and encryption. This guide explains how.

How to Protect a Document with a Smart Card & PKI Certificate

1. Understand the Basics
   • PKI Certificates: These are electronic ‘IDs’ that verify your identity and contain a public key. The smart card securely stores your private key, which is essential for signing and decrypting.
   • Digital Signatures: Using your private key on the smart card, you create a unique signature for the document. Anyone with your public key can verify it hasn’t been altered since it was signed.
   • Encryption: You can encrypt the document using the recipient’s public key (if they have one) so only they can decrypt it with their corresponding private key.
2. Software Requirements
   You’ll need software that supports smart card integration and PKI operations. Common options include:
   • OpenSSL: A powerful command-line tool for various cryptographic tasks (Linux, macOS, Windows).
   • Microsoft Outlook with a Smart Card CSP: For signing emails and documents directly within Outlook.
   • Adobe Acrobat Pro: Allows digital signatures in PDF documents.
   • Dedicated Signing Software: Many vendors offer software specifically for smart card-based document signing.
3. Signing a Document (Example using OpenSSL)

   This example assumes you have OpenSSL installed and your smart card reader is configured correctly.

   1. Find Your Certificate: Use OpenSSL to list the certificates on your smart card.

      openssl pkcs11 -t selftest

      This will show you details of the certificate(s) available. Note the label or alias for the signing certificate.

   2. Sign the Document: Use OpenSSL to create a digital signature file.

      openssl smime -sign -signer "Your Certificate Label" -inkfile document.txt -outform DER -output signed_document.sig

      Replace ‘Your Certificate Label’ with the label you identified in step 1 and ‘document.txt’ with your file name.

   3. Verify the Signature: Use OpenSSL to verify the signature.

      openssl smime -verify -in signed_document.sig -content document.txt

4. Encrypting a Document (Example using OpenSSL)

   This assumes you have the recipient’s public key in a file named recipient_public.pem.

   1. Encrypt the Document: Use OpenSSL to encrypt the document.

      openssl smime -encrypt -aes256 -in document.txt -outform DER -output encrypted_document.enc recipient_public.pem

      Replace ‘document.txt’ with your file name and ‘recipient_public.pem’ with the path to the recipient’s public key file.

   2. Decrypting the Document: The recipient will use their smart card and corresponding private key (and appropriate software) to decrypt the document.

      openssl smime -decrypt -in encrypted_document.enc -inkfile recipient_private.pem -outform DER -output decrypted_document.txt

5. Using Adobe Acrobat Pro
   • Open the document in Adobe Acrobat Pro.
   • Go to Tools > Digital Signatures.
   • Select ‘Sign with Smart Card’.
   • Follow the prompts to select your certificate and enter your PIN.
   • Acrobat will digitally sign the document, embedding the signature within the PDF file.
6. Important Considerations
   • Smart Card Reader: Ensure you have a compatible smart card reader and drivers installed.
   • PIN Protection: Always protect your smart card PIN. Do not share it with anyone!
   • Certificate Validity: Certificates expire. Regularly check the validity of your certificate and renew it when necessary.
   • cyber security Best Practices: Keep your software updated to protect against vulnerabilities. Be cautious about opening documents from unknown sources.