What Is Zero Trust Security? A Plain-English Guide
The old security model had a name, even if no one used it: “castle and moat.”
You built a perimeter—firewalls, VPNs, corporate networks—and trusted everyone inside it.
NDSS 2025 – A Comprehensive Study Of Security Risks In Deno And Its Ecosystem
The old security model had a name, even if no one used it: “castle and moat.”
You built a perimeter—firewalls, VPNs, corporate networks—and trusted everyone inside it. If you made it past the drawbridge, you were assumed to be legitimate. The moat was your security.
That model worked tolerably well when employees sat in offices, apps lived on local servers, and the internet was simpler. It hasn’t worked for a long time.
Today, your users are everywhere. Your applications live in AWS, Azure, and five other clouds. Your vendors have access to your systems. Your own employees connect from coffee shops and home networks. The “inside” doesn’t exist anymore—and yet many organizations still operate as if it does.
Zero Trust is the architecture built for the world we actually live in.
Where Zero Trust Came From
The term was coined by John Kindervag in 2010 during his time at Forrester Research. His observation was simple but radical: the assumption of trust inside a network was the fundamental flaw in enterprise security.
He wasn’t wrong. In 2010, attackers had already figured out that getting past the perimeter was the easy part. Once inside, they could move laterally for months, sometimes years, without detection. The average dwell time—the gap between initial breach and discovery—was measured in hundreds of days.
The problem wasn’t bad firewalls. It was the assumption that network location equaled trustworthiness.
Zero Trust proposed a different assumption: nothing is trusted by default. Not a device on the corporate network. Not an employee with valid credentials. Not a service calling another internal service. Every access request must be verified, every time.
Google operationalized this idea starting around 2014 with their BeyondCorp initiative—moving away from a privileged corporate network and treating every employee device as if it were on an untrusted network. That real-world proof of concept changed how the industry thought about Zero Trust. It wasn’t theoretical anymore.
NIST formalized the framework in 2020 with Special Publication 800-207, which gave enterprises a concrete reference architecture to work from. By then, the shift was already underway. The pandemic in 2020 accelerated it dramatically—overnight, the perimeter everyone had been reluctantly maintaining simply ceased to exist as the entire workforce went remote.
The Three Core Principles
Zero Trust is built on three ideas. Everything else flows from them.
1. Never Trust, Always Verify
No user, device, or network connection is trusted by default—regardless of where it is or where it’s coming from. Access decisions are made based on identity, context, and policy, not network location.
This sounds obvious when stated plainly, but it represents a complete inversion of legacy thinking. In a traditional network, being on the VPN or the corporate LAN implicitly granted a level of trust. In a Zero Trust model, those signals carry no weight. You prove who you are and what you need, every time.
2. Least Privilege Access
Every user, application, and system should have access only to what it specifically needs to do its job—and nothing more. Access should be scoped to the minimum required, granted for the minimum necessary time, and revoked the moment it’s no longer needed.
This principle limits the blast radius when something goes wrong. If an attacker compromises an account with least privilege access, they inherit only that account’s narrow permissions. If they compromise an over-provisioned admin account, they potentially own your entire infrastructure.
3. Assume Breach
Operate as if an attacker is already inside your environment. Design your systems so that a single compromised component can’t cascade into a catastrophic failure. This mindset changes how you build everything—network segmentation, logging, detection, response.
“Assume breach” doesn’t mean accepting defeat. It means building for resilience. It means your monitoring and detection capabilities matter as much as your prevention controls.
What Zero Trust Is Not
There’s significant confusion in the market—much of it deliberately created by vendors trying to sell you something.
Zero Trust is not a product. You cannot buy a Zero Trust appliance. Any vendor telling you their single product delivers Zero Trust is either confused or misleading you. Zero Trust is an architectural approach implemented through a combination of technologies, policies, and practices.
Zero Trust is not a project with an end date. It’s a continuous process. Environments change, new systems are added, threats evolve. Zero Trust requires ongoing maintenance and improvement.
Zero Trust is not just about authentication. Strong authentication is a critical component, but Zero Trust also encompasses device health verification, network segmentation, continuous monitoring, data classification, and behavioral analytics.
Zero Trust is not only for large enterprises. The principles apply at any scale. A 50-person company with cloud infrastructure and remote employees benefits from Zero Trust thinking just as much as a Fortune 500 firm.
The Seven Pillars
NIST’s framework and subsequent industry interpretations generally identify seven pillars that together constitute a Zero Trust architecture. Think of these as the domains where Zero Trust principles must be applied:
Identity: Who is accessing the system? This is the foundation. Strong identity verification—including multi-factor authentication, identity governance, and continuous authentication—is the starting point for all Zero Trust decisions.
Devices: What device is being used, and is it in a known, healthy state? A valid user on a compromised device is still a risk. Device health must be evaluated alongside identity.
Networks: Traffic should be segmented, encrypted, and continuously monitored—regardless of whether it’s crossing public internet or internal networks. Microsegmentation limits lateral movement if a breach occurs.
Applications and workloads: Applications should authenticate and authorize every request, validating that the caller is who they claim to be and that the request is appropriate given the context. This applies to human users and machine-to-machine calls alike.
Data: What data is being accessed, and is this access appropriate? Data classification, rights management, and access policies ensure that sensitive information isn’t available to everyone who can log in.
Visibility and analytics: Continuous monitoring, logging, and behavioral analytics are what make Zero Trust operational. Without visibility, you can’t enforce policy or detect anomalies.
Automation and orchestration: At enterprise scale, Zero Trust controls can’t be operated manually. Automation handles policy enforcement, anomaly response, and lifecycle management.
How Zero Trust Actually Works in Practice
Here’s a concrete scenario. A developer at your company opens their laptop at a coffee shop and tries to access your internal code repository.
In a legacy model, the answer might be: “They’re on the VPN, they’re authenticated—let them in.”
In a Zero Trust model, the system evaluates multiple signals before granting access:
Is this a managed corporate device? Is it running compliant software?
Is the user’s identity verified with a second factor?
Is the user’s login pattern consistent with their history? Same general location, same time of day?
What specifically are they trying to access, and do their permissions cover it?
Does the device meet your current security policy requirements?
Access is granted for the specific resource requested, with continuous re-evaluation throughout the session. If something changes—the device starts exhibiting unusual behavior, or the user attempts to access a resource outside their normal scope—the session can be flagged or terminated.
This is what “continuous validation” means. It’s not just authentication at login. It’s ongoing assessment throughout every session.
Why Zero Trust Matters Now More Than Ever
The threat landscape has changed substantially. The tools available to attackers have become dramatically more sophisticated. AI is now being used to craft phishing messages that are indistinguishable from legitimate communications. Credential theft has become industrialized. The supply chain has become a primary attack vector.
At the same time, the environments we need to protect have grown exponentially more complex. Cloud. Multi-cloud. SaaS. APIs. Third-party integrations. Remote workforce. Contractors. Machine-to-machine communication now accounts for a significant share of enterprise traffic.
The 2020 SolarWinds breach illustrated the limits of perimeter-based thinking with brutal clarity. Attackers inserted malicious code into a software update that was distributed to thousands of organizations. Once that update was installed inside trusted networks, the perimeter offered no protection at all.
Zero Trust doesn’t make you immune. No security model does. But it limits the blast radius, improves detection speed, and removes the single-point-of-failure that is implicit trust in the network.
Getting Started: A Practical First Step
The most common mistake organizations make when starting a Zero Trust initiative is trying to boil the ocean. Zero Trust is a journey, not a one-time deployment.
Start with identity. Get a clear picture of every user account in your environment—employees, contractors, service accounts. Implement strong multi-factor authentication. Enforce least privilege. Understand who has access to what, and audit it.
That single step—hardening identity and access management—delivers more security value than almost anything else you can do. It’s also the foundation everything else builds on.
From there, you add device health validation, network segmentation, application-level controls, and improved visibility layer by layer. Each step makes the environment more defensible.
The goal isn’t perfection. It’s continuous progress toward an architecture where trust is never assumed, always verified, and constantly re-evaluated.
The Bottom Line
Zero Trust is the right security model for the world we actually operate in—distributed, cloud-native, remote-work-first, and under constant attack.
It’s not a silver bullet. It’s not a product you can purchase. It’s a philosophy backed by architecture, implemented incrementally, and maintained continuously.
The organizations taking it seriously are the ones that understand security isn’t a project you complete. It’s a capability you build, and Zero Trust gives you a framework for building it right.
Deepak Gupta is the Co-founder & CEO of GrackerAI and an AI & Cybersecurity expert with 15+ years in digital identity and enterprise security. He writes about cybersecurity, AI, and B2B SaaS at guptadeepak.com.
*** This is a Security Bloggers Network syndicated blog from Deepak Gupta | AI & Cybersecurity Innovation Leader | Founder's Journey from Code to Scale authored by Deepak Gupta – Tech Entrepreneur, Cybersecurity Author. Read the original post at: https://guptadeepak.com/what-is-zero-trust-security-a-plain-english-guide/
About Author
