I know that there is a very similar question to that Is NFS Secure Over Internet, but I am asking a little bit different.
I guess that NFS is not so secure, as I can learn from the internet and from that question.
Are there any very secure methods to use in order for your employees to have access to some files you want to be very secure?
Let's say it a little different. If NSA for example, has some documents, lets say top secret, and wants those documents to be available to its employees (NSA may want each employee to have access to different documents according with what they are working on) but no-one else, and under no circumstances someone from inside or outside of the agency could have access to files that should not see, what NSA may do?
I am not just asking for NFS here, but everything that NSA could use to achieve it's purpose.