IEC 62443 Security Levels (SL)

    Understand SL-T, SL-C, and SL-A targets, then use QuantLayer to validate capability and measure posture continuously.

    IEC 62443
    Security Levels
    Risk
    7 min
    Last updated: 2026-01-22

    Overview

    IEC 62443 defines Security Levels (SL) as a measure of confidence that a zone or conduit is free from vulnerabilities and functions as intended. SLs reflect assumed capability and potential threat motivation, driving enhancements.

    SL-T, SL-C, SL-A

    SL-T (Target): Desired security level for a zone/conduit, derived from risk assessments and documented in the Cybersecurity Requirements Specification (CRS).

    SL-C (Capability): What a system or component can provide when properly configured—used to select products and compensating controls.

    SL-A (Achieved): Actual security level in operation, measured through continuous monitoring, maintenance, and evidence.

    Operationalizing SL in QuantLayer

    • Identity strength: hardware-rooted identity, enrollment coverage, credential lifecycle integrity.
    • Access posture: least-privilege rules enforced, exceptions tracked, step-up verification when needed.
    • Integrity posture: secure boot evidence, firmware/config drift, tamper events, remediation status.
    • Segmentation posture: allowed conduits, blocked flow trends, and change approvals.
    • Response readiness: alert-to-action timelines, automated containment, and incident reporting.

    Example: setting SL-T per zone

    • Safety zone: high SL-T, strong integrity monitoring, strict conduit controls, minimal remote access.
    • Control zone: high availability requirements, staged enforcement, maintenance-window changes.
    • Site DMZ: strong monitoring, brokered services, and tight control of inbound/outbound flows.
    • Business/IT zone: standard enterprise controls integrated with OT boundaries and logging.
    Tip
    QuantLayer lets you apply different enforcement modes per zone, so you can meet stronger targets where needed without disrupting deterministic processes.
    Implementation note
    IEC 62443 compliance is achieved through a combination of people, process, and technology controls. QuantLayer helps you operationalize the technical controls (identity, segmentation, integrity, telemetry, response) while producing audit-ready evidence to support your CSMS and assurance activities.