C2MS11 — Add Message-level Security Constructs

Add fields that allow encryption of content sections of C2MS messages as well as message signatures or message authentication codes. This would not assume or provide any particular mechanism to encrypt/sign, but would allow for tracking of these fields to aid usage.

The benefit of doing this is to allow the Mission to determine levels of security and secure componentry, but to use the message definition as a way to track this information.

Note that currently, GMSEC provides a level of encryption/signing, but my thought is that it would be preferred to allow the mission to manage this outside the transport layer. Providing encryption/signing FIELDS in the message definition allows for this decouplling.

I've got some specific ideas about how to do this, which I can share, but just want to capture the need here.