Most of the application protocols in use are still insecure and unencrypted. So, you set up little VPNs between each host, and you tunnel some applications over SSH or SSL. But that still doesn't work because you've now got a problem of transitive trust. If host A talks to host B and host B talks to host C, then a vulnerability in host B leaves host A open to attack from host C. Transitive trust is the "secret killer" of computer security but most of the time we never bump up against it in practice because it's easier for hackers to get in via simpler methods.

Whenever someone tells you that there's a novel, easy, solution to security, it's either because they don't understand security or they're trying to sell you something that isn't going to work.

In order to build really secure systems you need to understand the trust relationships between your systems and then build your systems to enhance and support your mission based on those trust relationships. But that's hard work that very few people have the courage and patience to undertake.

The computer security industry is trapped in this backwards mindset in which its practitioners keep trying to "list and deny all the things that are bad" rather than "list and permit all the things that are necessary and good"