Digital Certificates

http://jsignpdf.sourceforge.net/en_US/faq.html
http://docs.oracle.com/javaee/6/tutorial/doc/bnbxw.html
http://docs.oracle.com/javaee/1.4/tutorial/doc/Security6.html
http://docs.oracle.com/javase/6/docs/technotes/tools/solaris/keytool.html
http://www.sslshopper.com/article-most-common-java-keytool-keystore-commands.html