The notion of a zero trust networks (ZTN) was created in 2010 by John Kindervag, then of Forrester. Kindervag felt that as enterprises moved slowly towards a data-centric world with shifting threats and perimeters, a new concept of what constituted a secure network had to be created. It was ahead of its time and to a degree still is.

In a world of zero trust, all network traffic is considered untrusted. What this means from a security perspective is that anything that connects to that network must be fully secured. Much of a ZTN is predicated on strong authentication and access control, rounded out by effective data inspection and logging.

Most security professionals, and especially those studying for the CISSP exam, by default think of the 3-tier network architecture of the Internet, DMZ and trusted internal network. The ZT model throws that away and treats every device as if it’s an untrusted internet facing host. This means that every host on the internal network is considered hostile and compromised. To say this can create cognitive dissonance for some information security professionals is an understatement.

In Zero Trust Networks: Building Secure Systems in Untrusted Networks (O’Reilly Media 978-1491962190), authors Evan Gilman and Doug Barth have written a first-rate guide that details the core concepts of ZTN, in addition how to implement them. Note to the reader, if you think that designing and building a ZTN is plug and play, think again. Parenthetically, the authors write of the dangers of UPnP, which can allow any application to reconfigure a device. In the ZT model, this would never occur as there is a chain of trust between the host policies.

At the recent RSA Conference 2018, there were a few vendors touting zero trust solutions. The concept is still a few years away from being ubiquitous, but it is growing. From a security perspective, it is certainly an idea whose time has come. But the future growth of ZTN will likely be quite slow.

So just what is this thing called a ZTN? The book notes that a ZTN is built on these fundamental assertions:

1. The network is always assumed to be hostile.
2. External and internal threats exist on the network at all times.
3. Network locality is not sufficient for deciding trust in a network.
4. Every device, user, and network flow is authenticated and authorized.
5. Policies must be dynamic and calculated from as many sources of data as possible.

For those who thought PKI was dead, the authors write that all ZTN rely on PKI to prove identity throughout the network. But while public PKI are trusted by the internet at large, the authors write that it is not recommended for use in a ZTN.

A ZTN is particularly valuable when it comes to mobile devices. The authors write that surprisingly neither iOS nor Android ship with a host-based firewall. For those, the ZT model introduces the concept of single packet authentication (SPA) to reduce the attack surface on a mobile, or in fact, any host.

Chapter 9 details how to actually create a ZTN. The ZTN is predicated on 7 fundamental concepts. A few of them include that all network flows must be authenticated before being processed, all network flows should be encrypted before being transmitted, all network flows must be enumerated so that access can be enforced by the system, and more. Implementing those concepts is a challenge, but the benefits of a ZTN are quite compelling and make security sense. This chapter should be seen as a high-level introduction to the topics, as the notion of building a ZTN is far too complex and challenging to be fully covered in this 34-page chapter.

The authors are not so naïve to think that ZTN are a complete information security panacea. They are honest enough to note that ZTN, like every technology, protocol and the like are subject to attack. The book closes with how adversaries could attack a ZTN. From social engineering, DDoS and more, these must be considered when deploying a ZTN.

The concept of a ZTN forces network designers to rethink almost everything they know about security network design. As attacks get more sophisticated and network perimeters become more porous, the need for a ZTN will become more compelling. A ZTN is leading-edge infosec, but it won’t likely stay that way for much longer.

ZTN moves security from the network, obliterates the notion of a perimeter, and places it in the realm of identity and application-based security. For those looking to get a head-start on what the future of a secure network may look like, Zero Trust Networks: Building Secure Systems in Untrusted Networks is an excellent reference to get a solid introduction on the concept.