X.509 Digital Signatures/Encryption workflow/library recommendations?

Question

My particular use case is that I have to access digital certificates stored on the client, and use them to perform tasks of signing, verifying, encryption and decryption on

Answer 1

My best bet would still be an applet since that's possibly the most cross-platform thing. Alternately, I can develop my own activeX and limiting my reach.

Remember that client side certificate access is big security thing.