Bug Correction on SignedMessage

To allow a better compatibility with all
the ways to build a message (problems with part/alternative using
certain patterns).

Better Error Handling when openssl fails

Change-Id: I54f8e095099dc8904de51df064f7051fbe5fa17d
Add complete exception messages

Change-Id: If0d1b125ee5d64a897a7c39036fd71a1825db5b6