What is Zero Trust?

Traditional security was built mainly around dividing the corporate network into an "inside" and an "outside" with a perimeter, treating the inside as trusted and protecting it accordingly. However, with the spread of cloud services and the growth of remote work, the data and users to be protected have moved outside the corporate network, and the very distinction between "inside" and "outside" is losing its meaning.

This is where Zero Trust was born — an approach that verifies each individual access as the starting point, rather than relying on location. Zero Trust is generally designed along the following principles.

• ✓Verify every access. Whether inside or outside the network, confirm the legitimacy of each request every time.
• ✓Least privilege. Grant users and devices only the scope they need for their work.
• ✓Monitor and log continuously. Keep an ongoing understanding of who accessed what.
• ✓Decide based on ID and device. Determine access based on the user and device state, not the network location.

An analogy: an ID badge still gets checked at every room

Rather than "once you're in, you can roam freely," your identity and permission are checked every time, at each room (system).

Before / after: front door only, or every time

Traditionally, a check at the front door (perimeter) let you roam freely inside. Zero Trust verifies at every access and grants only the needed scope with least privilege.

Step by step: how a verified access flows

Every access verifies the user, device, and context, then grants only the needed scope with least privilege — and everything is logged and monitored.

A term often discussed alongside Zero Trust is "SASE." The two are not competing, separate things — they play different roles.

Zero Trust is a concept (a design philosophy) of "never trust, always verify." SASE, on the other hand, is one of the means of realizing that concept as a combination of network and security mechanisms. In other words, Zero Trust is the direction you are aiming for, and SASE is one of the options for translating it into a concrete mechanism.

~600 employees, service industry

Challenge: Once users entered the corporate network via VPN, they could broadly access internal systems and file servers. If an account were ever compromised, the damage could spread across the entire company. There were also concerns about whether accounts and permissions for departing or transferred employees were being properly revoked.

Existing environment: Internal access assumed VPN. Multiple sites and remote work were mixed, and user management was fragmented across departments.

• 1Centralized user IDs with Entra ID and introduced multi-factor authentication (MFA).
• 2Brought work devices under management so their state can be confirmed.
• 3Moved from a "see everything once inside" state to access scoped down per application.
• 4Monitored access logs and continuously reviewed policies.

Result: Even if an account is misused, the scope of damage is limited to a portion and lateral spread across the company can be prevented. When employees leave or transfer, permissions can be centrally cut off by disabling the ID, and the company can now protect itself by the same standard from anywhere — HQ, branches, or home — whether inside or outside the network.

• QWhat is Zero Trust?
  It is a security design philosophy based on the idea of "never trust, always verify." It discards the assumption that "being inside the corporate network is safe," and instead checks the user, the device, and the context every time access is requested.
• QHow does it differ from traditional perimeter defense?
  Traditional security divided the corporate network into an inside and an outside with a perimeter, treating the inside as trusted. Zero Trust verifies each individual access as the starting point rather than relying on location, so being inside the perimeter is not treated as safe.
• QWhat are the key principles of Zero Trust?
  Verify every access, grant only the scope needed for the work (least privilege), monitor and log continuously, and decide based on the user and device state rather than the network location.
• QHow does Zero Trust relate to SASE?
  Zero Trust is a concept (a design philosophy) of "never trust, always verify." SASE is one of the means of realizing that concept as a combination of network and security mechanisms.
• QWhere should a mid-sized company start?
  Since it is not completed all at once, a realistic approach is to first assess the current state, then proceed in stages starting from building the ID foundation with Entra ID and multi-factor authentication (MFA).