The lines of trust, trust boundaries, or trusted configuration lines in Cyber Security — essentially, how systems, devices, and users establish and maintain trust through configuration settings and security policies.

Trust Lines / Trust Boundaries

These define what components trust each other and where trust should stop. It’s a core idea in security architecture.

• A firewall marking the boundary between a trusted internal network and the untrusted
• A DMZ (demilitarized zone) between a public web server and a private database server.

• Zero Trust Architecture removes implicit trust between segments and always verifies.

Configuration Areas Related to Trust

• Network Trust Configuration
  VLANs and subnets with defined trust levels.
  Firewall rules to segment traffic.

  VPN configurations for secure remote access.

• Identity & Access Management (IAM)
  Configuring SSO, MFA, and role-based access control (RBAC).
  Trust relationships between domains or identity providers (e.g., SAML, OAuth).

  Federation trusts in Active Directory.

• Certificate & PKI Configuration
  Trust stores (trusted root CAs) on clients and servers.
  Certificate pinning or validation logic.

  TLS/SSL configuration settings.

• Endpoint Security Configuration
  Trusted boot and secure boot.
  Application allowlisting (e.g., Microsoft AppLocker).

  Trusted platform modules (TPM) for hardware trust.

• Cloud & API Trust Settings
  API key management and token scopes.
  Cloud IAM policies for cross-account access.

  Identity federation between cloud providers.

Lines of Configuration That Define Trust

These are often policy-driven or infrastructure-defined. Think of them as literal "lines" in config files or settings that define trusted behavior:

Examples :

• trusted_hosts = ["10.0.0.1", "10.0.0.2"]
• AllowUsers admin@trusted.domain.com
• trust-policy.json (AWS IAM or GCP IAM)
• /etc/hosts.allow and /etc/hosts.deny

• Azure conditional access policies defining trusted locations/devices.

Best Practices

• Least privilege: Trust as little as possible by default.
• Explicit trust: Define it clearly, avoid implicit assumptions.
• Segment and isolate: Use microsegmentation or container isolation.
• Audit and monitor: Track how trust is established and used.

• Automate validation: CI/CD tools and policy-as-code (e.g., OPA) can validate trust configs.