# Zero trust architecture

Zero trust architecture (ZTA) or perimeterless security is a design and implementation strategy of IT systems. The principle is that users and devices should not be trusted by default, even if they are connected to a privileged network such as a corporate LAN and even if they were previously verified.
ZTA is implemented by establishing identity verification, validating device compliance prior to granting access, and ensuring least privilege access to only explicitly-authorized resources. Most modern corporate networks consist of many interconnected zones, cloud services and infrastructure, connections to remote and mobile environments, and connections to non-conventional IT, such as IoT devices.
The traditional approach by trusting users and devices within a notional "corporate perimeter" or via a VPN connection is commonly not sufficient in the complex environment of a corporate network. The zero trust approach advocates mutual authentication, including checking the identity and integrity of users and devices without respect to location, and providing access to applications and services based on the confidence of user and device identity and device status in combination with user authentication. The zero trust architecture has been proposed for use in specific areas such as supply chains.
The principles of zero trust can be applied to data access, and to the management of data. This brings about zero trust data security where every request to access the data needs to be authenticated dynamically and ensure least privileged access to resources. In order to determine if access can be granted, policies can be applied based on the attributes of the data, who the user is, and the type of environment using Attribute-Based Access Control (ABAC). This zero-trust data security approach can protect access to the data.

## History

In April 1994, the term "zero trust" was coined by Stephen Paul Marsh in his doctoral thesis on computer security at the University of Stirling. Marsh's work studied trust as something finite that can be described mathematically, asserting that the concept of trust transcends human factors such as morality, ethics, lawfulness, justice, and judgement.
The problems of the Smartie or M&M model of the network (the precursor description of de-perimeterisation) was described by a Sun Microsystems engineer in a Network World article in May 1994, who described firewalls' perimeter defence, as a hard shell around a soft centre, like a Cadbury Egg.
In 2001 the first version of the OSSTMM (Open Source Security Testing Methodology Manual) was released and this had some focus on trust. Version 3 which came out around 2007 has a whole chapter on Trust which says "Trust is a Vulnerability" and talks about how to apply the OSSTMM 10 controls based on Trust levels.
In 2003 the challenges of defining the perimeter to an organisation's IT systems was highlighted by the Jericho Forum of this year, discussing the trend of what was then given the name "de-perimeterisation".
In response to Operation Aurora, a Chinese APT attack throughout 2009, Google started to implement a zero-trust architecture referred to as BeyondCorp.
In 2010 the term zero trust model was used by analyst John Kindervag of Forrester Research to denote stricter cybersecurity programs and access control within corporations. However, it would take almost a decade for zero trust architectures to become prevalent, driven in part by increased adoption of mobile and cloud services.
In 2018, work undertaken in the United States by cybersecurity researchers at NIST and NCCoE led to the publication of NIST SP 800-207 – Zero Trust Architecture. The publication defines zero trust (ZT) as a collection of concepts and ideas designed to reduce the uncertainty in enforcing accurate, per-request access decisions in information systems and services in the face of a network viewed as compromised. A zero trust architecture (ZTA) is an enterprise's cyber security plan that utilizes zero trust concepts and encompasses component relationships, workflow planning, and access policies. Therefore, a zero trust enterprise is the network infrastructure (physical and virtual) and operational policies that are in place for an enterprise as a product of a zero trust architecture plan.
There are several ways to implement all the tenets of ZT; a full ZTA solution will include elements of all three:
* Using enhanced identity governance and policy-based access controls.
* Using micro-segmentation
* Using overlay networks or software-defined perimeters
In 2019 the United Kingdom National Cyber Security Centre (NCSC) recommended that network architects consider a zero trust approach for new IT deployments, particularly where significant use of cloud services is planned. An alternative but consistent approach is taken by NCSC, in identifying the key principles behind zero trust architectures:
* Single strong source of user identity
* User authentication
* Machine authentication
* Additional context, such as policy compliance and device health
* Authorization policies to access an application
* Access control policies within an application