How to digitally sign...

all kinds of things for your client side attack

http://blog.didierstevens.com/2009/01/05/howto-add-a-digital-signature-to-an-office-document/

http://blog.didierstevens.com/2009/01/04/howto-add-a-digital-signature-to-a-pdf-file/

http://blog.didierstevens.com/2008/12/31/howto-add-a-digital-signature-to-executables/

http://blog.didierstevens.com/2009/01/01/howto-add-a-digital-signature-to-a-firefox-add-on/

and how to make your own cert

http://blog.didierstevens.com/2008/12/30/howto-make-your-own-cert-with-openssl/