Web application to sign PDF documents with digital certificates released by CAs
This sounds like something from EU. Unfortunately there are countless of different existing online signature plugins. Keep in mind that many depend on the client side software as well (if the certificates come from a smart card, smart card middleware usually needs to be present as well). So you better study your target market.
Immagine a web application written in python/django in which users authenticate with digital certificates via apache+mod_ssl (and a custom django authentication backend), how can they sign files then? The certificates are released by government approved CAs.
If I'm not wrong, a file needs to be signed with the private key of a certificate, because that is the proof that the file has been really signed by someone (and not someone-else pretending to be someone).
How can a web application have access to the private key of a certificate stored in the browser of the user?
Is this possible without the need of a software running on the user's machine?
EDIT:
So this can be done either with an ActiveX control or a Java applet, right? Does this need to be developed from scratch or does anybody know an open source solution?