How to Sign PDFs Server-Side with User-Provided Signatures: A Guide to Methods and Challenges?

Signing PDFs Server-Side with User-Provided Signatures

In this scenario, you require a server-based solution to sign PDFs using signatures obtained from users' local computers. Since the signature is not stored on the server, the task involves relaying the signature from the user's machine to the server for document signing.

Possible Approaches

1. Client-Side Signing:

If the certificate with the private key resides on the client's computer, you will need a client-side module to facilitate signing. JavaScript alone cannot access the client-side key. Java applets, however, can be employed to perform signing operations.

2. Distributed Signature Add-On:

Products like SecureBlackbox offer distributed signature add-ons that support signing PDFs remotely. These add-ons include pre-built browser modules (Java Applet, ActiveX, Flash), allowing you to transfer hashes from the server to the client for signing and embed the signature in the document.

Challenges and Considerations

One challenge with this approach is calculating and passing the hash from the server to the client for signing. It may be easier to transfer the entire document to the client and have them sign and upload it back to the server using client-side signing solutions like Java applets (with iText or SecureBlackbox Java Edition).

Possible Libraries

• SecureBlackbox Distributed Signature Add-on
• iText Java Edition

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