Long Term Content Protection

[LisToFacTor]

There is, perhaps, a wider perspective on the problem discussed
in this thread.

GPG is a reasonable tool for the protection and verification of
content exchanged between two parties. Once a message reaches
the recipient's operational environment, it should be decrypted,
and its further protection is best addressed as part and parcel
of the protection of that complete environment. After all, a message
of any consequence will likely result on secondary content
generated by and on the recipient's computer, that needs as much
(or more) protection as the message content in transit.

There are many tools and techniques for achieving that, but their
use and best practices are beyond the scope of this list.